Journal of Cellular Physiology

Axon regrowth is a key determinant of the restoration of the biological function of the nervous system after trauma. However, mature mammalian neurons have limited capacity for axon regeneration. We have previously demonstrated that neuronal axon growth both in the central and the peripheral nervous systems is markedly enhanced when non-muscle myosin II (NMII) is inhibited with blebbistatin. The activity of NMII is primarily regulated by MLCK and MLCP via the phosphorylation and dephosphorylation of its light chain, respectively; however, the functional roles of MLCK and MLCP in mammalian axonal regeneration remain unknown. In the present study, we provide strong evidence that the inhibition of MLCK activity significantly blocks axon regeneration in mice. Conversely, the inhibition of MLCP promotes axon regrowth of both the peripheral and central nervous system. Our findings further indicate that the MLCK/MLCP regulates axon regeneration and redistributes the growth cone F-actin, and this result suggests that direct regulation of the growth cone machinery is a potential strategy to promote axon regeneration.

Paravertebral muscle (PVM) abnormalities play important roles in the pathogenesis of idiopathic scoliosis (IS), and elevated oxidative stress could result in PVM injury in IS patients, but the underlying mechanism of oxidative stress generation is still unclear. Increased apoptosis, impaired myogenesis and elevated oxidative stress were found in primary skeletal muscle mesenchymal progenitor cells (hSM-MPCs), which are essential for the myogenesis process of vertebrate skeletal muscles, of IS patients. Through RNA-sequencing and further analysis, we identified significantly upregulated myostatin (MSTN) in IS hSM-MPCs. Overexpression of MSTN in hSM-MPCs from control patients increased the expression of NADPH oxidase 4, promoted reactive oxygen species production and apoptosis, and suppressed myogenesis. However, MSTN knockdown decreased the expression of NADPH oxidase 4, inhibited reactive oxygen species production and apoptosis, and enhanced myogenesis in IS hSM-MPCs. In addition, overexpression of MSTN in the PVMs of mice induced elevated oxidative stress and scoliosis without abnormal vertebral structure. Altogether, our study suggested that abnormal PVM changes and accumulated oxidative stress in IS patients may result from upregulation of MSTN, which could contribute to the development of IS.

Cells rapidly lose their physiological phenotype upon disruption of their extracellular matrix (ECM)-intracellular cytoskeleton interactions. Here, we investigated acute effects of ECM disruption on cellular and mitochondrial morphology, transcriptomic signatures, and Ca2+ handling in adult mouse skeletal muscle fibers. Adult skeletal muscle fibers were isolated from mouse toe muscle either by collagenase-induced dissociation of the ECM or by mechanical dissection that leaves the contiguous ECM intact. Experiments were generally performed four hours after cell isolation. At this time, there were striking differences in the gene expression patterns between fibers isolated with the two methods; 24h after cell isolation, enzymatically dissociated fibers had transcriptomic signatures resembling dystrophic phenotypes. Mitochondrial appearance was grossly similar in the two groups, but 3D electron microscopy revealed shorter and less branched mitochondria in enzymatically dissociated than in mechanically dissected fibers. Similar increases in free cytosolic [Ca2+] during repeated tetanic stimulation were accompanied by marked mitochondrial Ca2+ uptake only in enzymatically dissociated muscle fibers. The aberrant mitochondrial Ca2+ uptake was partially prevented by the mitochondrial Ca2+ uniporter inhibitor Ru360 and by cyclosporine A and NV556, which inhibit the mitochondrial protein Ppif (also called cyclophilin D). Importantly, inhibition of Ppif with NV556 significantly improved survival of mice with mitochondrial myopathy in which muscle mitochondria take up excessive amounts of Ca2+ even with an intact ECM. In conclusion, skeletal muscle fibers isolated by collagenase-induced dissociation of the ECM display aberrant mitochondrial Ca2+ uptake, which involves a Ppif-dependent mitochondrial Ca2+ influx resembling that observed in mitochondrial myopathies.

When viruses like SARS-CoV-2 infect cells, they reprogram the repertoire of cellular and viral transcripts that are being translated to optimize their strategy of replication, often targeting host translation initiation factors, particularly eIF4F complex consisting of eIF4E, eIF4G and eIF4A. A proteomic analysis of SARS-CoV-2/human proteins interaction revealed viral Nsp2 and initiation factor eIF4E2, but a role of Nsp2 in regulating translation is still controversial. HEK293T cells stably expressing Nsp2 were tested for protein synthesis rates of synthetic and endogenous mRNAs known to be translated via cap- or IRES-dependent mechanism under normal and hypoxic conditions. Both cap- and IRES-dependent translation were increased in Nsp2-expressing cells under normal and hypoxic conditions, especially mRNAs that require high levels of eIF4F. This could be exploited by the virus to maintain high translation rates of both viral and cellular proteins, particularly in hypoxic conditions as may arise in SARS-CoV-2 patients with poor lung functioning.

BackgroundThe intracellular Na+ concentration ([Na+]i) is a crucial but understudied regulator of cardiac myocyte function. The Na+/K+ ATPase (NKA) controls the steady-state [Na+]i and thereby determines the set-point for intracellular Ca2+. Here, we investigate the nanoscopic organization and local adrenergic regulation of the NKA macromolecular complex and how it differentially regulates the intracellular Na+ and Ca2+ homeostases in atrial and ventricular myocytes. MethodsMulticolor STORM super-resolution microscopy, Western Blot analyses, and in vivo examination of adrenergic regulation are employed to examine the organization and function of Na+ nanodomains in cardiac myocytes. Quantitative fluorescence microscopy at high spatiotemporal resolution is used in conjunction with cellular electrophysiology to investigate intracellular Na+ homeostasis in atrial and ventricular myocytes. ResultsThe NKA1 (NKA1) and the L-type Ca2+-channel (Cav1.2) form a nanodomain with a center-to center distance of [~]65 nm in both ventricular and atrial myocytes. NKA1 protein expression levels are [~]3 fold higher in atria compared to ventricle. 100% higher atrial INKA, produced by large NKA "superclusters", underlies the substantially lower Na+concentration in atrial myocytes compared to the benchmark values set in ventricular myocytes. The NKAs regulatory protein phospholemman (PLM) has similar expression levels across atria and ventricle resulting in a much lower PLM/NKA1 ratio for atrial compared to ventricular tissue. In addition, a huge PLM phosphorylation reserve in atrial tissue produces a high {beta}-adrenergic sensitivity of INKA in atrial myocytes. {beta}-adrenergic regulation of INKA is locally mediated in the NKA1-Cav1.2 nanodomain via A-kinase anchoring proteins. ConclusionsNKA1, Cav1.2 and their accessory proteins form a structural and regulatory nanodomain at the cardiac dyad. The tissue-specific composition and local adrenergic regulation of this "signaling cloud" is a main regulator of the distinct global intracellular Na+ and Ca2+ concentrations in atrial and ventricular myocytes.

Cardiac injury is common in hospitalized COVID-19 patients and portends poorer prognosis and higher mortality. To better understand how SARS-CoV-2 (CoV-2) damages the heart, it is critical to elucidate the biology of CoV-2 encoded proteins, each of which may play multiple pathological roles. For example, CoV-2 Spike glycoprotein (CoV-2-S) not only engages ACE2 to mediate virus infection, but also directly impairs endothelial function and can trigger innate immune responses in cultured murine macrophages. Here we tested the hypothesis that CoV-2-S damages the heart by activating cardiomyocyte (CM) innate immune responses. HCoV-NL63 is another human coronavirus with a Spike protein (NL63-S) that also engages ACE2 for virus entry but is known to only cause moderate respiratory symptoms. We found that CoV-2-S and not NL63-S interacted with Toll-like receptor 4 (TLR4), a crucial pattern recognition receptor that responsible for detecting pathogen and initiating innate immune responses. Our data show that the S1 subunit of CoV-2-S (CoV-2-S1) interacts with the extracellular leucine rich repeats-containing domain of TLR4 and activates NF-kB. To investigate the possible pathological role of CoV-2-S1 in the heart, we generated a construct that expresses membrane-localized CoV-2-S1 (S1-TM). AAV9-mediated, selective expression of the S1-TM in CMs caused heart dysfunction, induced hypertrophic remodeling, and elicited cardiac inflammation. Since CoV-2-S does not interact with murine ACE2, our study presents a novel ACE2-independent pathological role of CoV-2-S, and suggests that the circulating CoV-2-S1 is a TLR4-recognizable alarmin that may harm the CMs by triggering their innate immune responses.

Homeostatic calcium ion (Ca2+) fluxes between the endoplasmic reticulum, cytosol, and extracellular space occur not only in response to cell stimulation but also in unstimulated cells. Using murine astrocytes as a model, we asked whether there is a signaling function of these resting Ca2+-fluxes. The data showed that endoplasmic reticulum (ER) Ca{superscript 2} depletion, induced by sarcoplasmic/endoplasmic reticulum Ca{superscript 2}-ATPase (SERCA) inhibition, resulted to prolonged Ca{superscript 2} influx and mitochondrial fragmentation within 10 to 30 minutes. This mitochondrial fragmentation could be prevented in Ca2+- free medium or by inhibiting store-operated Ca2+ entry (SOCE). Similarly, attenuation of STIM proteins, which are vital ER Ca2+ sensors, protected mitochondrial morphology. On the molecular level, ER Ca2+ depletion, achieved either by removing extracellular Ca2+ or through acute SERCA inhibition, led to changes in gene expression of about 13% and 41% of the transcriptome within an hour, respectively. Transcriptome changes were associated with universal biological processes such as transcription, differentiation, or cell stress. Strong increase in expression was observed for the transcription factor ATF4, which is under control of the kinase PERK (EIF2AK3), a key protein involved in ER stress. Corroborating these findings, PERK was rapidly phosphorylated in Ca2+-free medium or after acute pharmacological inhibition of SOCE. In summary, resting, homeostatic Ca2+ fluxes prevent immediate- early cell stress and transcriptional reprogramming.

Phenotypic plasticity of vascular smooth muscle cells (VSMCs) under stress is believed to be a key factor in neointima formation. Lactate dehydrogenase A (LDHA), a key enzyme for glycolysis, has been demonstrated to promote the proliferation and migration of VSMCs. However, the mechanism by which LDHA regulates this process is still unclear. Here we show that the crotonylation and mono-ubiquitination of LDHA are increased in platelet-derived growth factor (PDGF)-BB-induced proliferative VSMCs. Crotonylation at lysine 5 (K5) activates LDHA through tetramer formation to enhance lactate production and VSMCs growth. Mono-ubiquitination at K76 induces the translocation of LDHA into mitochondria, which promotes mitochondria fission and subsequent the formation of lamellipodia and podosomes, thereby enhancing VSMC migration and growth. Furthermore, the increase of crotonylation and ubiquitination were also observed in the carotid arteries of ligation injury mice. Deletion of LDHA K5 crotonylation or K76 mono-ubiquitination decreases ligation-induced neointima formation. Our study reveals a novel mechanism that combines VSMC metabolic reprogramming and behavioral abnormity through crosstalk between LDHA K5 crotonylation and K76 mono-ubiquitination.

BackgroundMyocarditis is one of the most common health problems in young people. Despite imaging techniques and endomyocardial biopsies advancing, there is still inadequate for myocarditis characterization. Some studies have shown that myocarditis is closely associated with mitochondrial dysfunction. Therefore, this study was aimed to identify mitochondrial-related biomarkers and gene regulatory networks in myocarditis and potential therapeutic targets. MethodsWe downloaded GSE95368 dataset from GEO to get myocarditis gene expression profiles, then used EdgeR and AI algorithm for bioinformatics analysis of DEGs functions. Established CVB3-induced mouse myocarditis model via intraperitoneal injection, and assessed energy metabolism differences using targeted metabolomics. CVB3 stimulus induced myocarditis in H9C2 cells. We assessed mitochondrial dysfunction (ATP, MMP) with commercial kits, MAPK8 release via ELISA, and MAPK8, p-PI3K, p-AKT levels by western blot. Furthermore, a total of 8 patients primarily diagnosed with myocarditis were enrolled, and levels of MAPK8 and CK in serum were detected. SP600125, an inhibitor of MAPK8, was administrated to CVB3-infected mice to study its potential protective effect in viral myocarditis. ResultsWe obtained 77 DEGs enriched in myocarditis. Analysis yielded 11 modules, MEpurple module genes linked to myocarditis progression were identified via WGCNA. MAPK8, NAMPT and ALB are associated with mitochondrial function. CVB3-infected mice showed cardiac inflammation and high MAPK8 expression in serum or heart tissues.The target metabolism results indicated altered central carbon metabolism distinguished CVB3 group from control, with higher D-Glucose-1-phosphate and D-Glucose-6-phosphate and lower L-Cystine, dCMP, IMP and Xylulose-5-phosphate levels. CVB3 treatment caused mitochondrial dysfunction in H9C2 cells (decreased ATP, MMP), and increased MAPK expression. Western blot showed MAPK8 consolidated the levels of p-PI3K and p-AKT. CK activity was notably higher in myocarditis patients than healthy individuals. MAPK8 levels in myocarditis patients serum also exceeded those in healthy individuals. Pearson analysis indicated that MAPK8 and CK may contribute to myocarditis progression via distinct mechanisms. In CVB3-infected mouse model with SP600125 treatment, cardiac inflammation and MAPK8, p-PI3k, p-AKT expression were reduced, confirming MAPK8s crucial role in viral myocarditis. ConclusionOur study identified MAPK8 as a key biomarker of myocarditis, and it may be a potential therapeutic target for myocarditis.

The immune and metabolic responses of macrophages are closely linked, and mitochondria play a key role in polarizing them into pro-inflammatory (classical) and anti-inflammatory (alternative) states. Mitochondrial uncoupling protein 2 (UCP2) is involved in regulating macrophage inflammation and glucose metabolism; however, its regulatory mechanisms are unclear. We found that inflammatory stimuli reduce UCP2 expression and oxygen consumption rates (OCR), indicating mitochondrial suppression. Conversely, IL-4-activated macrophages displayed higher UCP2 levels and enhanced respiration. Under glucose deprivation, LPS-stimulated macrophages retained mitochondrial activity despite lower UCP2 levels. Pyruvate emerged as a key regulator of UCP2, blocking its mitochondrial entry reduced UCP2 expression. Additionally, hypoxia markedly decreased UCP2 levels in IL-4-activated macrophages, suggesting that hypoxia contributes to UCP2 suppression in pro-inflammatory macrophages. Notably, pro-inflammatory macrophages exhibit reduced reliance on UCP2 due to suppressed mitochondrial respiration. Pyruvate regulates UCP2 expression, highlighting the connection between glycolysis and mitochondrial metabolism. These findings may inform therapeutic strategies for diseases involving immune dysregulation.

Basal expression of the P2X7 receptor (P2X7R) improves mitochondrial metabolism, ATP synthesis and overall fitness of immune and non-immune cells. We investigated P2X7R contribution to energy metabolism and subcellular localization in fibroblasts (mouse embryo fibroblasts and HEK293 human fibroblasts), mouse microglia (primary brain microglia and the N13 microglia cell line), and heart tissue. The P2X7R localizes to mitochondria, and its lack a) decreases basal respiratory rate, ATP-coupled respiration, maximal uncoupled respiration, resting mitochondrial potential, mitochondrial matrix Ca2+ level, b) modifies expression pattern of oxidative phosphorylation (OxPhos) enzymes, and c) severely affects cardiac performance. Hearts from P2rx7-deleted versus WT mice are larger, heart mitochondria smaller, and stroke volume (SV), ejection fraction (EF), fractional shortening (FS) and cardiac output (CO), are significantly decreased. Accordingly, physical fitness of P2X7R-null mice is severely reduced. Thus, the P2X7R is a key modulator of mitochondrial energy metabolism and a determinant of physical fitness.

Muscle proteins of the obscurin protein family play important roles in sarcomere organization, sarcoplasmic reticulum (SR) and T-tubule architecture and function. However, their precise molecular functions and redundancies between protein family members as well as their involvement in cardiac diseases remain to be fully understood. To investigate the functional roles of obscurin and its close homologue obscurin-like 1 (Obsl1) in the heart, we generated and analyzed knockout mice for obscurin, Obsl1, as well as obscurin/Obsl1 double-knockouts (dKO). We show that dKO mice are viable but show postnatal deficits in cardiac muscle SR and mitochondrial architecture and function at the microscopic, biochemical and cellular level. Altered SR structure resulted in perturbed calcium cycling, while mitochondrial ultrastructure deficits were linked to decreased levels of Chchd3, a Micos complex protein. Hearts of dKO mice also show increased expression of Atg4d, a novel Obsl1 interacting protein, resulting in abnormal mitophagy and increased unfolded protein response. At the physiological level, loss of obscurin and Obsl1 resulted in a profound delay of cardiac relaxation, associated with metabolic signs of heart failure. Taken together, our data suggest that obscurin and Obsl1 play crucial roles in cardiac SR structure, calcium cycling, mitochondrial function, turnover and metabolism.

Parenthood has long been associated with gender disparities in academia. Yet, the underlying mechanism of how parenting is associated with career achievement gaps of academics remains unclear. Using data from a large-scale survey distributed to 7,764 scholars and their publication profiles from the Web of Science database, we analyze the gender differences in parenthood, academic achievements, and the mediation effect of work-family conflict and partner support in these gender gaps. Our results suggest that gender gaps in academic achievements are in fact "parenthood gaps". Specifically, we found significant gender gaps exist in all measures of objective and subjective career achievements of academics in the parent group but not in the non-parent group. Additionally, mothers are more likely than fathers to experience higher levels of work-family conflict, and receive lower levels of partner support, contributing significantly to the gender gaps in objective and subjective career achievements for the parent group. Findings from this study identify the forms and the impact of parenthood on gender disparities in career achievements of academics and shed light on possible interventions and actions for mitigating gender inequalities in academia.

Ventricular remodeling is one of the primary adaptive mechanisms in response to long-term mechanical overload in diabetes. In addition to cardiomyocyte hypertrophy, alterations in noncardiomyocyte compartments [e.g. extracellular matrix (ECM)] are an essential process in the remodeling of ventricle during diabetes. Integrins that link the ECM and intracellular cytoskeleton function as mechanotransducers to translate the mechanical force to intracellular signals. We hypothesize that mechanotransduction mechanisms are altered in diabetic cardiomyopathy mouse hearts. To test this hypothesis, force and intracellular calcium ([Ca2+]i) measurements on papillary muscle fibers were investigated in adult mouse cardiomyocytes from normal (non-db) and type 2 diabetic (db/db) mice. In addition, atomic force microscopy (AFM) was used to measure adhesion force between integrin receptors and ECM protein fibronectin (FN) by quantifying the unbinding force required to break FN-cardiomyocytes (integrin) bonds. In db/db mice, the peak active force decreased at 71% or 73% while the peak of [Ca2+]i decreased at 64% and 68% at 1 Hz or 2 Hz. In the presence of the FN (35 nM), active force was increased significantly by 40-50% in db/db mice. Furthermore, increased active force in the presence of FN was associated with 26-42% increase in [Ca2+]i at all giving stimulations of 1 Hz and 2 Hz in db/db mice, respectively. The increased effects on force and [Ca2+]i caused by FN were greater in ventricular muscles from db/db mice than from non-db mice. The unbinding force between FN (2.7 M) coated AFM probes and cardiomyocyte in db/db was 52% higher than non-db (58.3 {+/-} 0.3 pN vs 38.6 {+/-} 0.9 pN. p < 0.05). The binding probability of FN-cardiomyocytes, calculated as number of force curves with adhesion / number of total force curves sampled, was significantly reduced by 30% in db/db cardiomyocytes when compared to normal. In addition, the cell stiffness, representing changes in Ca2+ signaling and cytoskeletal reorganization, was 19% increase in db/db cardiomyocytes. The presented data indicate that dynamic changes of the mechanical properties of integrin-ECM interactions may contribute to impaired intracellular Ca2+ signaling and myofilament activation in the diabetic cardiomyopathy.

The high interstitial ATP concentration in the cancer microenvironment is a major source of adenosine, which acts as a strong immune suppressor. However, the source of ATP release has not been elucidated. We measured the ATP release during hypotonic stress using a real-time ATP luminescence imaging system in primary cultured mammary cells and in breast cell lines. In primary cultured cells, ATP was intermittently released with transient-sharp peaks, while in breast cell lines ATP was released with a slowly rising diffuse pattern. The diffuse ATP release pattern was changed to a transient-sharp pattern by cholera toxin treatment and the reverse change was induced by transforming growth factor (TGF) {beta} treatment. DCPIB, an inhibitor of volume-regulated anion channels (VRACs), only suppressed the diffuse pattern. The inflammatory mediator sphingosine-1-phosphate (S1P) induced a diffuse ATP release pattern isovolumetrically. The knockdown of A isoform of leucine-rich repeat-containing protein 8 (LRRC8A), the essential molecular entity of VRACs, using shRNA suppressed the diffuse pattern. These results suggest that abundantly expressed VRACs are a conduit of ATP release in undifferentiated cells, including cancer cells.

Historically women have been underrepresented in STEM careers. While the number of women receiving doctorate degrees in the biological sciences has exceeded the number of men since approximately 2005, there is still a disparity between the sexes at more advanced career stages. Achieving equity is an important social goal and there is an expected benefit to science since diverse groups outperform homogeneous groups. There are many factors that contribute to the disparity between men and women in science, including a disparity in research productivity. While many studies have documented this "productivity paradox" and examined factors driving this disparity, few studies have addressed differences in productivity between men and women doctoral students. This is an important population to assess since the individuals are in the formative stages of their academic career and differences in productivity could have a significant impact on career progression. This study addresses this question and identified more than 42,000 doctoral students in the biological and biomedical sciences working with over 16,000 advisors at 235 institutions in the United States and finds a disparity in research productivity between men and women. Men produce >10% more first author papers, >15% more total papers and their first author papers receive >17% more citations. The findings establish the generality of the gender gap in research productivity among doctoral students in the biological and biomedical sciences. Redressing this gap at the formative stage of young scientists careers, when they are establishing their credentials to advance in their field, is important to address the disparity between the sexes in the biomedical workforce.

BackgroundFrom single-cellular to multicellular organisms, a natural nonspecific immune system, called the K+/Na+ innate immune system, has recently been proposed to play an important role in the process of fighting against viral infection, however, there is little direct research evidence. This study aimed to evaluate whether the changes in serum K+/Na+ concentrations are associated with susceptibility and severity of SARS-CoV-2 infection. MethodsWe systematically searched PubMed, the Web of Science Core Collection, MedRxiv and BioRxiv databases for articles published between Jan 1, 2020 and Dec 14, 2022. We extracted the serum K+/Na+ concentration data of patients with COVID-19 from 112 published studies after removing inappropriate articles according to the defined criteria and analyzed the relationship between the serum k+/Na+ concentrations and the illness severity of patients. Then we used a cohort of 244 patients with COVID-19 for a retrospective analysis. ResultsThe mean serum k+/Na+ concentrations in patients with COVID-19 were 3.99 and 138.0 mmol/L, respectively, which were much lower than the mean levels in the population (4.40 and 142.0, respectively). The mean serum Na+ concentration in severe/critical patients (136.8) was significantly lower than those in mild and moderate patients (139.4 and 138.0, respectively). Such findings were confirmed in a retrospective cohort study, of which the mean serum k+/Na+ concentrations in all patients were 4.0 and 137.5 mmol/L, respectively. The significant differences in serum Na+ concentrations were found between the mild (139.2) and moderate (137.2) patients, and the mild and severe/critical (136.6) patients, which were correlated to the illness severity of patients. ConclusionsThese findings may indicate the importance of a natural immune system constructed by intracellular potassium and extracellular sodium ions in the fight against viral infection and provide new ideas for the prevention and treatment of COVID-19.

All-trans retinoic acid (ATRA) increases the sensitivity to unfolded protein response (UPR) in differentiating leukemic blasts. The downstream transcriptional factors of PERK, a major arm of UPR, regulates muscle differentiation. However, the role of growth arrest and DNA damage-inducible protein 34 (GADD34), one of the downstream factors of PERK, and the effects of ATRA on GADD34 expression in muscle remain unclear. In this study, we identified ATRA increased the GADD34 expression independent of the PERK signal in the gastrocnemius muscle of mice. ATRA up-regulated GADD34 expression through the transcriptional activation of it via inhibiting the interaction of homeobox Six1 and transcription co-repressor TLE3 with the MEF3-binding site on the GADD34 gene promoter in myoblasts. ATRA also inhibited the interaction of TTP, which induces mRNA degradation, with AU-rich element on GADD34 mRNA via p38 MAPK, resulting in the instability of GADD34 mRNA. Overexpressed GADD34 in myoblasts changes the type of myosin heavy chain in myotubes. These results suggest ATRA increases GADD34 expression via transcriptional and post-transcriptional regulation in myoblasts, which changes muscle fiber type in myotubes.

Skeletal muscle adaptation to exercise involves various phenotypic changes that enhance metabolic and contractile functions. One key regulator of these adaptive responses is the activation of AMPK, influenced by exercise intensity. However, the mechanistic understanding of AMPK activation during exercise remains incomplete. In this study, we utilized an in vitro model to investigate the effects of mechanical loading on AMPK activation and its interplay with the mTOR signaling pathway. Proteomic analysis of myoblasts subjected to static loading (SL) revealed distinct quantitative protein alterations associated with RNA metabolism, with 10% SL inducing the most pronounced response compared to lower intensity of 5% and 2% as well as control. Additionally, 10% SL suppressed RNA and protein synthesis, while activating AMPK and inhibiting the mTOR pathway. Our RNA sequencing analysis further corroborated these findings, revealing numerous differentially regulated genes and signaling pathways influenced by both AMPK and mTOR. Further examination showed that SL induced changes in mitochondrial biogenesis and the ADP/ATP ratio. These findings provide novel insights into the cellular responses to mechanical loading and shed light on the intricate AMPK-mTOR regulatory network in myoblasts.

Academic job markets have become increasingly challenging worldwide, yet it remains poorly characterized how competitively-successful candidates should be and what the underlying determinants of their success are. Focusing on the field of ecology and evolutionary biology, we analyzed the academic performance (measured as h-index) as well as the duration before recruitment as a new faculty member and promotion to full professor of 145 principal investigators (PI) over the past 34 years in Taiwan. We found that PIs had higher performance and longer duration before recruitment more recently. Performance before promotion remained stable, whereas the duration increased over time. The origin and prestige of doctorate had no effect on the performance or duration either before recruitment or before promotion. We also found that the difference in performance before and after recruitment ("After" performance -- "Before" performance) decreased in recent years, with PIs recruited in earlier years maintaining their performance after recruitment while those recruited in later years exhibiting a performance drop. While PIs performed equally well before and after recruitment irrespective of doctorate origin, those with domestic PhD degrees showed a decrease in performance after promotion compared to their counterparts with foreign degrees. Taken together, our findings reveal a prolonged career duration for researchers as a result of intensifying competition in academia, and highlight the increasingly crucial role of academic performance, rather than PhD degree itself, in determining academic success.