Frontiers in Physiology

Our study reveals that status of the sGC heterodimer or its subsequent activation aligns with active erythropoiesis, and this heterodimer also correlates with the expression of myoglobin (Mb) or HO1. In this study we found that Mb expression which is driven by iron restriction and high sGC activation in iron deficiency anemia (IDA) leaches out more into the serum relative to non-anemic WTs. Tissues from IDA mice of both models developed either by nutritional iron deprivation or by ablation of ferroportin (Fpn) gene or from iron refractory iron deficiency anemia (IRIDA) mice found that Mb expression follows a variable pattern in different tissues but always correlates to the status of the sGC heterodimer or its subsequent activation. Here higher Mb expression happening in anemic (IDA, Fe<5 ppm or IDA, Fpn) or non-anemic WT mice is both due to iron restriction and an elevated sGC heterodimer that corroborated with greater sGC activation. More importantly we find significant leaching of Mb into the serum of these anemic (IDA) mice from both models and our spectral data suggests that this Mb is heme-free. This Mb leaching in anemia is a cumulative impact of Mb secreting out from various tissues including lungs, spleen, skeletal or cardiac muscles where Mb is expressed and not just in the skeletal muscles where Mb expression is low. Based on these findings we construct a working model of anemia, where high activation of sGC under anemic conditions (Fpn ablation or restricted Fe diet) induces Apo-Mb or heme-free Mb expression which can then leach out into the serum. Our findings of Mb leaching are novel and can find further application as a diagnostic strategy in anemia.

Hypoxia underlies or complicates a wide range of chronic conditions, including cancer, arthritis, chronic pain, multiple sclerosis, stroke, chronic kidney disease, diabetes and more. Research is presented supporting indications that slower-paced exercises may develop states of relaxation, combined with enhanced respiration, which may trigger accelerated diffusion and facilitated oxygen use in the cells, stimulating cellular regeneration and healing. Metarobic theory is proposed as a physiological explanation for the benefits of slower-paced exercises, and as a good fit with aerobic and anaerobic categories of exercise. Metarobic theory posits that the momentary post activity drop in blood oxygen saturation (SpO2) following slow-paced exercises, and intermittently during sleep, may be the result of increased oxygen diffusion and metabolism. Metarobic effects may explain the non-aerobic health benefits of slower paces of walking, tai chi, qigong, and other slow-paced exercises, as well as the healing benefits of sleep. Research from the current study is presented, which supports that the momentary large drops in SpO2 ranging from 85% to 92% (m=89.2%{+/-}1.79) following slower-paced exercises, and periodically during sleep, may indicate a shift in the use and metabolism of oxygen. It is suggested that the momentary drop in SpO2 may follow an accelerated period of oxygen diffusion in response to hypoxic areas of the body, and a need for enhanced healing and cellular regeneration. In relation to sleep, this contrasts to current theory that lower levels of SpO2 during sleep result from more shallow respiration, due to the body needing less oxygen during sleep, resulting in hypoxemia. The end effect of slow-paced exercises and sleep may be to reverse or moderate hypoxia in the body through metarobic effects including enhanced oxygen diffusion, supporting healing and cellular regeneration.

Transverse (t)-tubules ensure a uniform rise in calcium (Ca2+) and thus contraction in cardiac cells. Though more extensively studied in the ventricle, t-tubules also play a key role in the atria of large mammals, such as human, and their loss in heart failure is associated with impaired Ca2+ release and thus contractility. T-tubule restoration is therefore an ideal therapeutic target but the process of t-tubule formation is not understood. The aim of this study was to determine how t-tubules develop in the healthy atria and the impact this has on Ca2+ handling. Postnatal development was assessed in sheep from newborn through to adulthood. Atrial t-tubules were present at birth in the sheep atria and increased in density up until 3 months of age. In the latter part of development (3 months to adult) a lack of t-tubule growth but increase in cell width results in t-tubule density decreasing. In the newborn, despite reduced t-tubule density, we found the amplitude of the Ca2+ transient was maintained and this was associated with increases in the L-type Ca2+ current (ICa-L) and the Ca2+ content of the sarcoplasmic reticulum (SR). We suggest these changes are sufficient to overcome the elevated cytosolic Ca2+ buffering in the newborn and the decreased t-tubule density. We have shown the neonate atria is highly specialised to negate reduced central Ca2+ release through enhanced surface ICa-L and SR load. This maintains atrial function despite immature t-tubules highlighting important differences in Ca2+ handling in the newborn and heart failure atria where t-tubules are sparse.

AimsThe behavior of pacemaker cardiomyocytes (PCs) in the sinoatrial node (SAN) is modulated by neurohormonal and paracrine factors, many of which signal through G-protein coupled receptors (GPCRs). The aims of the present study are to catalog GPCRs that are differentially expressed in the mammalian SAN and to define the acute physiological consequences of activating the cholecystokinin-A signaling system in isolated PCs. Methods and ResultsUsing bulk and single cell RNA sequencing datasets, we identify a set of GPCRs that are differentially expressed between SAN and right atrial tissue, including several whose roles in PCs and in the SAN have not been thoroughly characterized. Focusing on one such GPCR, Cholecystokinin-A receptor (CCKAR), we demonstrate expression of Cckar mRNA specifically in mouse PCs, and further demonstrate that subsets of SAN fibroblasts and neurons within the cardiac intrinsic nervous system express cholecystokinin, the ligand for CCKAR. Using mouse models, we find that while baseline SAN function is not dramatically affected by loss of CCKAR, the firing rate of individual PCs is slowed by exposure to sulfated cholecystokinin-8 (sCCK-8), the high affinity ligand for CCKAR. The effect of sCCK-8 on firing rate is mediated by reduction in the rate of spontaneous phase 4 depolarization of PCs and is mitigated by activation of beta-adrenergic signaling. Conclusions(1) PCs express many GPCRs whose specific roles in SAN function have not been characterized, (2) Activation of the the cholecystokinin-A signaling pathway regulates PC automaticity.

Inositol trisphosphate (IP3) is a major Ca2+-mobilising second messenger and atrial IP3 receptor (IP3R) expression is greatly increased in atrial fibrillation (AF). Cardiac atrial and sino-atrial node (SAN) myocytes also express Ca2+-stimulated adenylyl cyclases (AC1 and AC8); however the pathways underlying atrial AC1 and AC8 activation are unknown. We investigated whether IP3 signalling in cardiac atria and SAN utilises ACs. Immunocytochemistry in isolated guinea pig atrial myocytes identified co-localisation of type 2 IP3Rs with AC8, while AC1 was located in close vicinity. UV photorelease of IP3 significantly enhanced Ca2+ transient amplitudes following stimulation of atrial myocytes (31 {+/-} 6 % increase 60 s post photorelease, n=16), an effect abolished by inhibitors of ACs (MDL-12,330) or PKA (H89). The maximum rate change observed in spontaneously-beating murine right atrial preparations exposed to phenylephrine (14.7 {+/-} 0.5 %, n=10) was significantly reduced by 2.5 mol/L 2-APB and abolished by a low dose of MDL-12,330. These observations are consistent with a functional interaction between IP3 and cAMP signalling involving Ca2+ stimulation of ACs in cardiac atria and the SAN. Structural evidence supports AC8 as the most likely effector. This signal transduction mechanism is important for future study in atrial physiology and pathophysiology, particularly AF.

Volitional motor activity is associated with a feedforward cardiorespiratory response to actual or impending movements. We have previously shown in the CRC study that the expectation of physical exercise causes a decrease in cardiorespiratory coherence that scales with the anticipated load. The present work uses a modeling approach to investigate the mechanisms that can cause a fall in cardiorespiratory coherence (CRC). We devised a Hodgkin-Huxley model of a cardiac pacemaker cell using the NEURON module. We simulated the effect of autonomic tone, sympathetic & respiratory-vagal modulation, and respiratory irregularity on pacemaker cell output by injecting efflux/influx current to model the parasympathetic/sympathetic effects, respectively. The vago-sympathetic tone was modeled by altering the direct current bias of the injected current and the respiratory-vagal effect by the periodic modulation of the injected current at a frequency of 0.2 Hz, corresponding to a respiratory rate of 12 breaths/min. Sympathetic modulation was simulated by injecting a low-frequency current close to Mayer wave frequency (0.08 Hz). We computed the coherence between the instantaneous pacemaker rate and respiratory-vagal modulation current as a model analog to experimental CRC. We found that sympathetic modulation, low vagal tone/high sympathetic tone, and respiratory irregularity can cause a decrease in CRC. We corroborated the model results with the actual data from the CRC study. In conclusion, we employ a novel approach combining insights from the experimental study and a physiologically plausible modeling framework to understand the mechanisms underlying the fall of cardiorespiratory coherence induced by the expectation of exercise. NEW & NOTEWORTHY Cardiorespiratory coherence is diminished in response to respiratory irregularity, low vagal/high sympathetic tone, and prominent low-frequency sympathetic modulation. Expectation of physical activity induces respiratory irregularity and increased sigh frequency and that contributes to diminished cardiorespiratory coherence in expectation of exercise. There is a greater fall of coherence with the non-linear (logistic) transformation of injected current, indicating the non-linear nature of cardiorespiratory interactions preceding the onset of exercise.

Traumatic Brain Injury (TBI) can alter the brains ability to maintain an adequate supply of oxygen and metabolites to brain tissue by disrupting the autoregulatory mechanisms that maintain constant cerebral blood flow. Impaired cerebral autoregulation can result in brain hypoxia leading to morbidity and mortality so maintenance of cerebral blood flow after injury is of paramount importance. Currently, this is managed using limited information and various assumptions, hence there is significant interest in developing better correlates for establishing whether cerebral autoregulation is impaired or intact. In this study we simultaneously measure cerebral blood flow (CBF) using a non-invasive optical approach, intracranial pressure (ICP, measured invasively) and arterial blood pressure (ABP) with the aim of investigating the relationships between these signals over multiple timescales, and ultimately assessing how these measurements may best be combined and interpreted to aid the treatment of TBI.

BackgroundIn addition to show autonomous beating rhythmicity, the physiological functions of the heart present daily periodic oscillations. Notably the ventricular repolarization itself varies throughout the circadian cycle which was mainly related to the periodic expression of K+ channels. However, the involvement of the L-type Ca2+ channel (CaV1.2 encoded by Cacna1c gene) in these circadian variations remains elusive. MethodsWe used a transgenic mouse model (PCa-luc) that expresses the luciferase reporter under the control of the cardiac Cacna1c promoter and analyzed promoter activity by bioluminescent imaging, qPCR, immunoblot, Chromatin immunoprecipitation assay (ChIP) and CaV1.2 activity. ResultsUnder normal 12:12h light-dark cycle, we observed in vivo a biphasic diurnal variation of promoter activities peaking at 9 and 19.5 Zeitgeber time (ZT). This was associated with a periodicity of Cacna1c mRNA levels preceding 24-h oscillations of CaV1.2 protein levels in ventricle (with a 1.5 h phase shift) but not in atrial heart tissues. The periodicity of promoter activities and CaV1.2 proteins, which correlated with biphasic oscillations of L-type Ca2+ current conductance, persisted in isolated ventricular cardiomyocytes from PCa-Luc mice over the course of the 24-h cycle, suggesting an endogenous cardiac circadian regulation. Comparison of 24-h temporal patterns of clock gene expressions in ventricles and atrial tissues of the same mice revealed conserved circadian oscillations of the core clock genes except for the retinoid-related orphan receptor gene (ROR), which remained constant throughout the course of a day in atrial tissues. In vitro we found that ROR is recruited to two specific regions on the Cacna1c promoter and that incubation with specific ROR inhibitor disrupted 24-h oscillations of ventricular promoter activities and CaV1.2 protein levels. Similar results were observed for pore forming subunits of the K+ transient outward currents, KV4.2 and KV4.3. ConclusionsThese findings raise the possibility that the ROR-dependent rhythmic regulation of cardiac CaV1.2 and KV4.2/4.3 throughout the daily cycle may play an important role in physiopathology of heart function.

AimTo identify the amino acids that stimulate glucagon secretion in mice and whether the metabolism of these relies on glucagon receptor signaling.\n\nMethodsPancreata of female C57BL/6JRj mice were perfused with 19 individual amino acids (1 mM) and secretion of glucagon was assessed using a specific glucagon radioimmunoassay. Separately, a glucagon receptor antagonist (GRA; 25-2648, 100 mg/kg) or vehicle was administered to female C57BL/6JRj mice three hours prior to an intraperitoneal injection of four different isomolar (in total 7 {micro}mol/g body weight) amino acid mixtures; mixture 1: alanine, arginine, cysteine, and proline; mixture 2: asparatate, glutamate, histidine, and lysine; mixture 3: citrulline, methionine, serine, and threonine; and mixture 4: glutamine, leucine, isoleucine, and valine. Blood glucose, plasma glucagon, amino acid, and insulin concentrations were measured using well characterized methodologies.\n\nResultsAlanine (P=0.03), arginine (P<0.001), and proline (P=0.03) but not glutamine (P=0.2) stimulated glucagon secretion from the perfused mouse pancreas. Cysteine had the numerically largest effect on glucagon secretion but did not reach statistical significance (P=0.08). However, when the four isomolar amino acid mixtures were administered there were no significant difference (P>0.5) in plasma concentrations of glucagon across mixture 1-4. Plasma concentrations of total amino acids were higher after administration of GRA when mixture 1 (P=0.004) or mixture 3 (P=0.04) were injected.\n\nConclusionOur data suggest that alanine, arginine, and proline but not glutamine are involved in the liver-alpha cell axis in mice as they all increased glucagon secretion and their disappearance rate was altered by GRA.\n\nGraphical abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC=\"FIGDIR/small/792119v2_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (19K):\norg.highwire.dtl.DTLVardef@b78a3corg.highwire.dtl.DTLVardef@1d475d1org.highwire.dtl.DTLVardef@1830a00org.highwire.dtl.DTLVardef@59c51_HPS_FORMAT_FIGEXP M_FIG C_FIG

Kidney function is regulated by the circadian clock. Not only do glomerular filtration rate (GFR) and urinary excretion oscillate during the day, the expressions of several renal transporter proteins also exhibit circadian rhythms. Interestingly, the circadian regulation of these transporters may be sexually dimorphic. Thus, the goal of this study is to investigate the mechanisms by which kidney function of the mouse is modulated by sex and time of day. To accomplish this, we have developed the first computational models of epithelial water and solute transport along the mouse nephrons that represent the effects of sex and circadian clock on renal hemodynamics and transporter activity. We conduct simulations to study how the circadian control of renal transport genes affects overall kidney function, and how that process differs between male and female mice. Simulation results predict that tubular transport differs substantially among segments, with relative variations in water and Na+ reabsorption along the proximal tubules and thick ascending limb tracking that of GFR. In contrast, relative variations in distal segment transport are much larger, with Na+ reabsorption almost doubling during the active phase. Oscillations in Na+ transport drive K+ transport variations in the opposite direction. Model simulations of BMAL1 knockout mice predict a significant reduction in net Na+ reabsorption along the distal segments in both sexes, but more so in males than females. This can be attributed to the reduction of mean ENaC activity in males only, a sex-specific effect that may lead to a reduction in blood pressure in males.

Calcium (Ca2+) and magnesium (Mg2+) are essential for cellular function. The kidneys play an important role in maintaining the homeostasis of these cations. Their reabsorption along the nephron is dependent on distinct trans- and paracellular pathways, and is coupled to the transport of other electrolytes. Notably, sodium (Na+) transport establishes an electrochemical gradient to drive Ca2+ reabsorption. Consequently, alterations in renal Na+ handling, under pathophysiological conditions or pharmacological manipulations, can have major effects on Ca2+ transport. One such condition is the administration of diuretics, which are used to treat a large range of clinical conditions, but most commonly for the management of blood pressure and fluid balance. While the pharmacological targets of diuretics typically directly mediate Na+ transport, they also indirectly affect renal Ca2+ and Mg2+ handling, i.e., by establishing a prerequisite electrochemical gradient. Thus, substantial alterations in divalent cation handling can be expected following diuretic treatment. To investigate renal Ca2+ and Mg2 handling, and how those processes are affected by diuretics treatment, we have developed sex-specific computational models of electrolyte transport along the nephrons. Model simulations indicate that along the proximal tubule and thick ascending limb, the transport of Ca2+ and Mg2+ occusr in parallel with Na+, but those processes are dissociated along the distal convoluted tubule. We also simulated the effects of acute administration of loop, thiazide, and K-sparing diuretics. The model predicted significantly increased Mg2+ excretion, no significant alteration in Mg2+ excretion, and significantly decreased Mg2+ excretion on treatment with loop, thiazide, and K-sparing diuretics, respectively, in agreement with experimental studies. The present models can be used to conduct in silico studies on how the kidney adapts to alterations in Ca2+ and Mg2+ homeostasis during various physiological and pathophysiological conditions, such as pregnancy, diabetes, and chronic kidney disease.

We introduce here a new multiplatform JAVA-based mathematical-computational model of RBC homeostasis for investigating the dynamics of changes in RBC homeostasis in health and disease. We provide a brief overview on the homeostasis of human RBCs and on the general biophysical principles guiding the modelling design. By way of a detailed tutorial we apply the model to investigate in depth the multiple effects associated with RBC dehydration induced by potassium permeabilization, a necessary preliminary for understanding the pathophysiology of a wide group of inherited haemolytic anaemias, a subject of intense current research and clinical interest. Using the red cell model (RCM), we design and run in silico representations of experimental protocols to study global RBC responses to calcium and potassium permeabilization covering a wide range of experimental, physiological and pathological conditions. Model outputs report the evolution in time of all the homeostatic variables in the system allowing, for the first time, a detailed and comprehensive account of the complex processes shaping global cell responses. Analysis of the results explains the mechanisms by which the entangled operation of all the RBC components link cell dehydration and protein crowding to cell acidification and to the generation of hypertonic, alkaline effluents. Open access to the RCM in a GitHub repository, together with the tutorial primed for a specific investigation pave the way for researchers and clinicians to apply the model on many different aspects of RBC physiology and pathology.

The major membrane currents responsible for sinoatrial and idioventricular rhythm-generation were studied in isolated rat heart preparations, perfused in Langendorff mode. The rates of whole isolated hearts beating with sinoatrial rhythm decreased with cesium and ivabradine, both blockers of the funny current, and were not affected by nickel, at a dose which blocks T-type calcium current. The sinoatrial rhythm was completely abolished by reduction or removal of sodium from the perfusate (interventions that inhibit calcium-extrusive mode of the sodium/calcium exchanger), or by nifedipine, an L-type calcium channel blocker. Idioventricular rhythm, however, was arrested only by reduction of sodium in the perfusate. Ivabradine reduced the idioventricular rate, nickel did not cause any change, while nifedipine in some cases increased it. The inferences made based on these observations are that INCX and ICaL are obligatory rhythm-generating currents in the sinoatrial node, while INCX is the only obligatory mechanism for an idioventricular rhythm. The funny current is not an obligatory requirement for sinoatrial as well as idioventricular rhythm-generation. However, it enhances the frequency of LCRs. Our results in the isolated whole heart are in corroboration with results from isolated cells.

O_LIGluconeogenesis (GNG) is the process of regenerating glucose and NAD+ that allows continuing ATP synthesis by glycolysis during fasting or in hypoxia. Recent data from C. elegans and crustaceans challenged with hypoxia show differential and tissue-specific expression of GNG-specific genes. C_LIO_LIHere we report differential expression of several GNG-specific genes in the head and body of a model organism, Daphnia magna, a planktonic crustacean, in normoxic and acute hypoxic conditions. We predict that GNG-specific transcripts will be enriched in the body, where most of the fat tissue is located, rather than in the head, where the tissues critical for survival in hypoxia, the central nervous system and locomotory muscles, are located. We measured the relative expression of GNG-specific transcripts in each body part by qRT-PCR and normalized them by either the expression of a reference gene or the rate-limiting glycolysis enzyme pyruvate kinase (PK). C_LIO_LIOur data show that of the three GNG-specific transcripts tested, pyruvate carboxylase (PC) showed no differential expression in either the head or body. Phosphoenolpyruvate carboxykinase (PEPCK-C), on the other hand, is upregulated in hypoxia in both body parts. Fructose-1,6-bisphosphatase (FBP) is upregulated in the body relative to the head and upregulated in hypoxia relative to normoxia, with a stronger body effect in hypoxia when normalized by PK expression. C_LIO_LIThese results support our hypothesis that Daphnia can survive hypoxic conditions by implementing the Cori cycle, where body tissues supply glucose and NAD+ to the brain and muscles, enabling them to continuously generate ATP by glycolysis. C_LI

The refractory period of cardiac tissue can be quantitatively described using strength-interval (SI) curves. The information captured in SI curves is pertinent to the design of anti-arrhythmic devices including pacemakers and implantable cardioverter defibrillators. As computational cardiac modelling becomes more prevalent, it is feasible to consider the generation of computationally derived SI curves as a supplement or precursor to curves that are experimentally derived. It is beneficial, therefore, to examine the profiles of the SI curves produced by different cardiac tissue models to determine whether some models capture the refractory period more accurately than others. In this study, we compare the unipolar SI curves of two tissue models: the current state-of-the-art bidomain model and the recently developed extracellular-membrane-intracellular (EMI) model. The EMI models resolution of individual cell structure makes it a more detailed model than the bidomain model, which forgoes the structure of individual cardiac cells in favour of treating them homogeneously as a continuum. We find that the resulting SI curves elucidate differences between the models, including that the behaviour of the EMI model is noticeably closer to the refractory behaviour of experimental data compared to that of the bidomain model. These results hold implications for future computational pacemaker simulations and shed light on the predicted refractory properties of cardiac tissue from each model. Author summaryMathematical modelling and computational simulation of cardiac activity have the potential to greatly enhance our understanding of heart function and improve the precision of cardiac medicine. The current state-of-the-art model is the bidomain model, which considers a volume average of cardiac activity. Although the bidomain model has had success in several applications, in other situations, its approach may obscure critical details of heart function. The extracellular-membrane-intracellular (EMI) model is a recently developed model of cardiac tissue that addresses this limitation. It models cardiac cells individually; therefore, it offers significantly greater physiological accuracy than bidomain simulations. This increase in accuracy comes at a higher computational cost, however. To explore the benefits of one model over the other, here we compare the performance of the bidomain and EMI models in a pacing study of cardiac tissue often employed in pacemaker design. We find that the behaviour of the EMI model is noticeably closer to experimental data than the behaviour of the bidomain model. These results hold implications for future pacemaker design and improve our understanding of the two models in relation to one another.

Cerebral autoregulation, the physiological capability to regulate cerebral blood flow, may be assisted by short-term mean arterial pressure control via baroreflex, which, among several effects, modulates total peripheral resistance. It is unclear, however, whether the resistance of the head and neck vasculatures is also affected by baroreflex and whether these extracranial vessels assist autoregulation. Since sensing technologies such as functional Near-Infrared Spectroscopy and noninvasive intracranial pressure monitoring by strain gauge may be influenced by superficial tissue, it is clinically relevant to understand the relations between intracranial and extracranial hemodynamics. Therefore, we created an autoregulation model consisting of arteries and arterioles regulated by the intralumial pressure and microcirculation regulated by local blood flow. As the first critical step to quantify the signal deterioration introduced by the extracranial circulation on superficial sensors, the extracranial peripheral circulation of the head and neck and baroreflex regulation of the peripheral vasculature and of heart rate were also included. During simulations of a bout of acute hypotension, the model predicts a rapid return of cerebral blood flow to baseline levels and a prolonged suppression of the blood flow to the external carotid vasculature, in accordance with experimental evidence. The inclusion of peripheral control via baroreflex at the external carotid vasculature did not assist cerebral autoregulation, thus we raise the hypothesis that baroreflex may act on the head and neck vasculatures but this action has negligible effects on regulation of cerebral blood flow. When autoregulation is impaired, results suggest that the blood flow of the brain and of the head and neck present similar dynamics, while they are weakly coupled when autoregulation is intact. The model also provides a mechanistic explanation of the protection brought by cerebral autoregulation to the microvasculature and to the brain parenchyma. Our model forms the foundation for predicting the interference introduced by the superficial tissue to nonivasive sensors.

Osteoporosis is a significant health and economic issue, as it predisposes patients to a higher risk of bone fracture. Measuring bone mineral density has been shown to be an accurate way to assess the risk for osteoporosis. The most common way for bone density testing is a dual-energy X-ray absorptiometry (DEXA) scan, which may be recommended for patients with increased risk of osteoporosis. Radiograph imaging is widely available in clinical settings and acquired for many reasons, such as trauma or pain. The goal of this project is to extract radiomics information from pelvic X-rays (both the hip and femoral neck regions) to assess the risk of osteoporosis (triaging patients into "normal" vs. "at-risk", or "low risk" vs. "high risk" categories). The motivation here is not to replace the DEXA scan but to proactively identify patients at risk for osteoporosis and appropriately refer them to management options. We apply machine learning-based radiomics techniques on a study cohort of 565 patients. Our preliminary results show that a correlation between the radiomics features extracted from pelvic X-rays and the level of osteoporosis risk derived from the DEXA test results.

In mammalian fat and muscle cells, insulin stimulates the translocation of the glucose transporter GLUT4 from intracellular storage compartments to the plasma membrane in adipocytes and muscle cells, significantly increasing glucose uptake. In unstimulated (basal) cells, GLUT4 is sequestered in non-cycling/very slowly cycling compartments. Insulin mobilizes GLUT4 by releasing it from sequestration, enabling its exocytosis and continuous cycling between the plasma membrane and endosomes. Upon insulin withdrawal, GLUT4 is rapidly internalized and re-sequestered internally for future activation. Dynamic studies using tagged GLUT4 have revealed that this trafficking mechanism is regulated post-translationally, with GLUT4 undergoing repeated cycles of mobilization and sequestration in response to fluctuating insulin levels. The trafficking of GLUT4 under basal and maximal insulin concentrations can be modeled as a single cycling pool, with different amounts of GLUT4 in the actively cycling pool. In this model, insulin regulates both the rate constant of exocytosis, kex, and the distribution of GLUT4 between the cycling and a non-cycling pool. Here, we present modeling of the kinetics of GLUT4 trafficking in 3T3-L1 adipocytes over a range of insulin concentrations, under steady state, and in transition after adding insulin or after adding an inhibitor of exocytosis. Given the observed characteristics of the experimental data, parsimonious explanatory models incorporating different hypotheses of the insulin-dependence of the GLUT4 recycling system are optimized to the data sets to identify dominant processes acting in the dynamics. The steady-state data is best fit with a model that includes a dose-dependent increase in the size of the cycling pool at submaximal insulin concentrations (quantal release). Simultaneous fits of the transition and steady-state data indicate that insulin regulates a second kinetics rate constant, in addition to increasing kex and the cycling pool size. SummaryExperimental and modeling investigations of the trafficking of GLUT4 in 3T3-L1 adipocytes at different insulin doses shows the dominant effects of the insulin dose on the dynamics. The data is best fit, particularly at submaximal insulin concentrations, by a model in which both the exocytosis rate and the size of the cycling pool increases with insulin.

Throughout pregnancy, the kidneys undergo significant adaptations in morphology, hemodynamics, and transport to achieve the volume and electrolyte retention required to support a healthy pregnancy. Additionally, during pregnancies complicated by chronic hypertension, altered renal function from normal pregnancy occurs. The goal of this study is to analyze how inhibition of critical transporters affects gestational kidney function as well as how renal function is affected during chronic hypertension in pregnancy. To do this, we developed epithelial cell-based multi-nephron computational models of solute and water transport in the kidneys of a female rat in mid- and late pregnancy. We simulated the effects of key individual pregnancy-induced changes on renal Na+ and K+ transport: proximal tubule length, Na+/H+ exchanger isoform 3 (NHE3) activity, epithelial Na+ channel activity (ENaC), K+ secretory channel expression, and H+-K+-ATPase activity. Additionally, we conducted simulations to predict the effects of inhibition and knockout of the ENaC and H+-K+-ATPase transporters on virgin and pregnant rat kidneys. Our simulation results predicted that the ENaC and H+-K+-ATPase transporters are essential for sufficient Na+ and K+ reabsorption during pregnancy. Last, we developed models to capture changes made during hypertension in female rats and considered what may occur when a rat with chronic hypertension becomes pregnant. Model simulations predicted that in hypertension for a pregnant rat there is a similar shift in Na+ transport from the proximal tubules to the distal tubules as in a virgin rat.

Calcium ion concentration modulates the function of pyruvate dehydrogenase, isocitrate dehydrogenase, and -ketoglutarate dehydrogenase. Previous studies have shown that despite its ability to affect the function of these dehydrogenases, [Ca2+] does not substantially alter mitochondrial ATP synthesis in vitro under physiological sub-strate conditions. We hypothesize that, rather than contributing to respiratory control, [Ca2+] governs fuel selection. Specifically, cardiac mitochondria are able to use different primary carbon substrates to synthesize ATP aerobically. To determine if and how [Ca2+] affects the relative use of carbohydrates versus fatty acids we measured oxygen consumption and tricarboxylic acid cycle intermediate concentrations in suspensions of cardiac mitochondria with different combinations of pyruvate and palmitoyl-L-carnitine in the media at various [Ca2+] and ADP infusion rates. Results reveal that when both fatty acid and carbohydrate substrates are available, fuel selection is sensitive to both calcium and ATP synthesis rate. When no Ca2+ is added under low ATP-demand conditions, {beta}-oxidation provides roughly half of acetyl-CoA for the citrate synthase reaction with the rest coming from the pyruvate dehydrogenase reaction. Under low demand conditions with increasing [Ca2+], the fuel utilization ratio shifts to increased fractional consumption of pyruvate, with 83{+/-}10% of acetyl-CoA derived from pyruvate at the highest [Ca2+] evaluated. With high ATP demand, the majority of acetyl-CoA is derived from pyruvate, regardless of the Ca2+ level. Our results suggest that changes in work rate alone are enough to effect a switch to carbohydrate use while in vivo the rate at which this switch happens may depend on mitochondrial calcium.\n\nKey PointsO_LIDespite its effects on activity of mitochondrial dehydrogenases, Ca2+ does not substantially alter mitochondrial ATP synthesis in vitro under physiological substrate conditions. Nor does is appear to play an important role in respiratory control in vivo in the myocardium.\nC_LIO_LIWe hypothesize that Ca2+ plays a role mediating the switch in fuel selection to increasing carbohydrate oxidation and decreasing fatty acid oxidation with increasing work rate.\nC_LIO_LITo determine if and how Ca2+ affects the relative use of carbohydrates versus fatty acids in vitro we measured oxygen consumption and TCA cycle intermediate concentrations in suspensions of purified rat ventricular mitochondria with carbohydrate, fatty acid, and mixed substrates at various [Ca2+] and ATP demand rates.\nC_LIO_LIOur results suggest that changes in work rate alone are enough to effect a switch to carbohydrate use in vitro while in vivo the rate at which this switch happens may depend on mitochondrial calcium.\nC_LI