Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease

We have generated using CRISPR/Cas9 technology a partially humanized mouse model of the neurometabolic disease phenylketonuria (PKU), carrying the highly prevalent PAH variant c.1066-11G>A. This variant creates an alternative 3 splice site, leading to the inclusion of 9 nucleotides coding for 3 extra amino acids between Q355 and Y356 of the protein. Homozygous Pah c.1066-11A mice, with a partially humanized intron 10 sequence with the variant, accurately recapitulate the splicing defect and present almost undetectable hepatic PAH activity. They exhibit fur hypopigmentation, lower brain and body weight and reduced survival. Blood and brain phenylalanine levels are elevated, along with decreased tyrosine, tryptophan and monoamine neurotransmitter levels. They present behavioral deficits, mainly hypoactivity and diminished social interaction, locomotor deficiencies and an abnormal hind-limb clasping reflex. Changes in the morphology of glial cells, increased GFAP and Iba1 staining signals and decreased myelinization are observed. Hepatic tissue exhibits nearly absent PAH protein, reduced levels of chaperones DNAJC12 and HSP70 and increased autophagy markers LAMP1 and LC3BII, suggesting possible coaggregation of mutant PAH with chaperones and subsequent autophagy processing. This PKU mouse model with a prevalent human variant represents a useful tool for pathophysiology research and for novel therapies development.

Acute liver failure is a life-threatening condition during infancy. Biallelic pathogenic variants in LARS1 cause infantile liver failure syndrome type 1 (ILFS1), which is characterized by acute hepatic failure in infants. LARS functions as a protein associated with mTORC1 and plays a crucial role in amino acid-triggered mTORC1 activation and autophagy regulation. A previous study demonstrated that larsb-knockout zebrafish show a condition resembling ILFS. However, a comprehensive analysis of larsb-knockout zebrafish has not yet been performed because of early mortality. We herein generated a long-term viable zebrafish model carrying a LARS1 variant identified in an ILFS1 patient (larsb-I451F zebrafish) and analyzed the pathogenesis of the affected liver of ILFS1. Hepatic dysfunction is most prominent in ILFS1 patients during infancy; correspondingly, the larsb-I451F zebrafish manifested hepatic anomalies during the developmental stages. The larsb-I451F zebrafish demonstrates augmented lipid accumulation within the liver under autophagy activation. Inhibition of DGAT1, which converts fatty acids to triacylglycerols, improved lipid droplets in the liver of larsb-I451F zebrafish. Notably, treatment with an autophagy inhibitor ameliorated hepatic lipid accumulation in this model. Our findings suggested that enhanced autophagy caused by biallelic LARS1 variants contributes to ILFS1-associated hepatic dysfunction. Furthermore, the larsb-I451F zebrafish model, which has a prolonged survival rate compared to the larsb-knockout model, highlights its potential utility as a tool for investigating the pathophysiology of ILFS1-associated liver dysfunction. Author SummaryInfantile liver failure (ALF) is a rare but life-threatening condition primarily caused by various genetic and infectious factors during infancy. Comprehensive research into its causes is crucial for treatment decisions, including liver transplantation and supportive interventions. While specific therapies exist for some conditions, a significant proportion of infant ALF cases remains unresolved. Recent advances in genetic sequencing have identified congenital disorders, particularly involving the LARS1 gene, as contributors to ALF. LARS1 is essential for regulating processes related to amino acids and autophagy. To better understand this condition, we created a zebrafish model carrying specific LARS1 gene variants seen in ALF patients. These zebrafish displayed liver abnormalities similar to those observed in infants with ALF. Our study revealed that enhanced autophagy, triggered by biallelic LARS1 variants, plays a significant role in liver dysfunction associated with ALF. Notably, inhibiting specific enzymes involved in fat metabolism and autophagy showed promising results in reducing hepatic lipid accumulation in our zebrafish model. This research provides insights that may lead to improved understanding and potential treatments for this devastating condition.

Macular corneal dystrophy (MCD) is a rare congenital disease caused by mutations in the carbohydrate sulfotransferase 6 (chst6) gene. Patients suffer from opaque aggregates in the cornea leading to bilateral progressive vision loss by 4th decade of life. Corneal transplantation is the only available treatment, which is invasive, not available to every patient and recurrence of the symptoms is common. Keratocytes in the cornea express the chst6 gene, which encodes a golgi enzyme that is essential for sulfation of the keratan sulfate proteoglycans (KSPG). The loss of KS sulfation leads to defects in collagen fibril organization and aggregate formation in the corneal extracellular matrix. Lack of preclinical disease models is a major limitation for the development of accessible treatment strategies. Attempts to develop mouse MCD models have failed due to lack of chst6 gene in mice and difference in proteoglycan composition of the mouse cornea. The zebrafish chst6 gene has not been studied previously. Zebrafish cornea structure is highly similar to humans, containing high levels of keratan sulfate proteoglycans in the stroma. Here, loss of function chst6 mutant zebrafish were generated with CRISPR/Cas9 mediated gene editing. Several chst6 alleles were obtained, and loss of KSPG sulfation in the eye stroma was shown. Mutant zebrafish developed age-dependent, alcian blue positive, opaque accumulates in the cornea. Degeneration of corneal structure and changes in epithelial thickness were observed. The zebrafish MCD model developed here is the first in vivo model of the disease and opens up possibilities to develop and screen treatment strategies. Significance StatementFirst in vivo model of macular corneal dystrophy (MCD) is reported in this study. Zebrafish model developed here paves the way for modeling of other corneal dystrophies in this aquatic vertebrate which is easy to apply therapeutics and image in vivo. The clinical symptoms of MCD are well reproduced in the zebrafish MCD model. Moreover, the authors showed that chst6 gene function is not restricted to cornea, and a fraction of mutant larvae have morphological defects. The mutants developed here provide a genetic model for understanding the highly complex roles of keratan sulfate proteoglycans.

Adiponectin receptor 1 (ADIPOR1) is a transmembrane protein necessary for normal anatomy and physiology in the retina. In a recent study of complement factor H knockout mice (Cfh-/-), our lab discovered a flecked retina phenotype and retinal thinning by fundus imaging and optical coherence tomography (OCT), respectively. The phenotype was observed in a subset (50%) of Cfh-/- mice. The thinning observed in vivo is due to an early degeneration of rod photoreceptors. This phenotype has not been reported in published studies of Cfh-/- mice. AdipoR1 knockout mice (AdipoR1-/-) and mice deficient in Membrane Frizzled Related Protein (MFRP) exhibit this phenotype, suggesting an involvement in the emergence of the retinal degeneration observed in a subset of Cfh-/- mice. Cfh and AdipoR1 are located in close proximity on mouse Chromosome 1 (Chr1) and a complementation cross between Cfh and AdipoR1 mice with retinal degeneration produced 100% progeny with retinal degeneration. Sequencing of the Cfh-/- mice revealed a c.841 C > T mutation in AdipoR1. Furthermore, one Cfh wildtype (of Cfh+/+) and 2 heterozygous (of Cfh+/-) mice exhibited retinal degeneration and were homozygous for the point mutation. The c.841 C > T mutation results in a proline to serine conversion at position 281 (P281S) in ADIPOR1. This residue is critical for ADIPOR1 open and closed conformations in the membrane. In silico modeling of candidate ADIPOR1 ligands, 11-cis-retinaldehyde and docosahexaenoic acid (DHA), that are deficient in AdipoR1-/-, suggests that ADIPOR1 is involved in trafficking retinoids and fatty acids and their combined deficiency in the ADIPOR1 mutant retinas might explain the retinal degeneration phenotype.

BackgroundIt was assumed that the cause of chronic inflammation in atherosclerosis is a disturbance of the innate immunity response, caused, among other factors, by mitochondrial dysfunctions. It was also suggested that mitochondrial dysfunction may be caused by heteroplasmic mutations in mitochondrial DNA. The aim of this study was to evaluate the effect of the mitochondrial nonsense mutation m.15059G>A on cellular functions in atherosclerosis: lipoidosis, pro-inflammatory response, and mitophagy. MethodsThe human monocytic cell line THP-1 and cytoplasmic hybrid cell line TC-HSMAM1 were used. An original approach based on the CRISPR/Cas9 system was developed and used for the elimination of mtDNA copies carrying the m.15059G>A mutation in the MT-CYB gene. Using this approach, the Cas9-TC-HSMAM1 cells with an eliminated m.15059G>A mutation was obtained. The gene expression levels of genes encoding enzymes related to cholesterol metabolism were analyzed by quantitative RT-PCR. The evaluation of pro-inflammatory cytokine secretion was assessed using ELISA. Mitophagy in cells was detected using confocal microscopy. ResultsIn contrast to intact TC-HSMAM1 cybrids, in Cas9-TC-HSMAM1 cells, incubation with atherogenic LDL led to a decrease in the expression of the gene encoding fatty acid synthase (FASN). It was found that TC-HSMAM1 cybrids are characterized by defective mitophagy and are also unable to reduce the production of pro-inflammatory cytokines (to form immune tolerance) in response to repeated LPS stimulation. Elimination of mtDNA carrying the m.15059G>A mutation led to the restoration of immune tolerance and activation of mitophagy in the studied cells. ConclusionsThe m.15059G>A mutation was found to be associated with defective mitophagy, immune tolerance, and impaired metabolism of intracellular lipids due to upregulation of the FASN. Thus, this mutation may play an important role in atherogenesis due to its contribution to the chronification of inflammation, which aggravates the progression of atherosclerosis.

Mutations in pre-mRNA processing factor 31 (PRPF31), a core protein of the spliceosomal tri-snRNP complex, cause autosomal-dominant retinitis pigmentosa (adRP). It has remained an enigma why mutations in ubiquitously expressed tri-snRNP proteins result in retina-specific disorders, and so far, the underlying mechanism of splicing factors-related RP is poorly understood. Here, we used iPSC technology to generate retinal organoids and RPE models from three patients with severe and very severe PRPF31-adRP, normal individuals and a CRISPR/Cas9-corrected isogenic control. To fully assess the impacts of PRPF31 mutations, quantitative proteomics analyses of retinal organoids and RPE cells was carried out showing RNA splicing, autophagy and lysosome, unfolded protein response (UPR) and visual cycle-related pathways to be significantly affected. Strikingly, the patient-derived RPE and retinal cells were characterised by the presence of large amounts of cytoplasmic aggregates containing the mutant PRPF31 and misfolded, ubiquitin-conjugated proteins including key visual cycle proteins, which accumulated progressively with time. Mutant PRPF31 variant was not incorporated into splicing complexes, but reduction of PRPF31 wildtype levels led to tri-snRNP assembly defects in Cajal bodies of PRPF31 patient retinal cells with reduced U4/U6 snRNPs and accumulation of U5, smaller nuclear speckles and reduced formation of active spliceosomes giving rise to global splicing dysregulation. Moreover, the impaired waste disposal mechanisms further exacerbated aggregate formation, and targeting these by activating the autophagy pathway using Rapamycin resulted in reduction of cytoplasmic aggregates and improved cell survival. Our data demonstrate that it is the progressive aggregate accumulation that overburdens the waste disposal machinery rather than direct PRPF31-initiated mis-splicing, and thus relieving the RPE cells from insoluble cytoplasmic aggregates presents a novel therapeutic strategy that can be combined with gene therapy studies to fully restore RPE and retinal cell function in PRPF31-adRP patients. HighlightsO_LIPRPF31 RP mutations lead to formation of insoluble aggregates containing the mutant PRPF31 and misfolded, ubiquitin conjugated proteins including key visual cycle proteins (e.g. RLBP1) in RPE cells, which accumulate progressively with time and affect tight junctions and cell survival. C_LIO_LIMutant PRPF31 is predominantly localised in cytoplasmic aggregates of patient specific RPE and retinal cells and is not able to be incorporated into splicing complexes to cause direct mis-splicing. C_LIO_LIHigh-throughput quantitative proteomics identifies significantly altered RNA splicing, visual perception, retinoid metabolism, waste disposal and unfolded protein response pathways in patient RPE cells, and autophagy and lysosome, unfolded protein response (UPR) and visual cycle-related pathways in photoreceptor cells. C_LIO_LIAccumulation of PRPF31 mutant variant as cytoplasmic aggregates reduces wildtype PRPF31 in the nucleus leading to tri-snRNP assembly defects, characterised by accumulation of U5 and reduction of U4/U6 snRNPs in Cajal bodies, altered morphology of nuclear speckles and consequently downregulation of active spliceosomes (Bact and C complexes) in PRPF31 patient RPE and retinal cells. C_LIO_LIProteomic study of insoluble aggregates identifies other RP-linked splicing factors and multiple key retinal-specific proteins, whose variants are linked to retinitis pigmentosa, within the aggregates of patient RPE cells. C_LIO_LIPRPF31 patient RPE cells have impaired waste disposal and proteasome mediated degradation, which together with the impaired autophagy pathway, further exacerbate aggregate formation. C_LIO_LIPhagocytosis of photoreceptor outer segment fragments (POS) shed daily by RPE cells accelerates aggregation of key proteins indicating enhanced cytoplasmic aggregate formation under physiological conditions in patient RPE cells. C_LIO_LIActivation of autophagy via administration of rapamycin results in reduction of cytoplasmic aggregates in RPE cells, correct localisation of mislocated and misfolded proteins to the nucleus, thereby improving cell survival. C_LI

The ALMS1 gene plays a crucial role in maintaining cellular homeostasis through its involvement in primary cilium assembly, cytoskeletal regulation, and signalling pathways such as NOTCH and TGF-{beta}. Pathogenic variants in ALMS1 are associated with Alstrom Syndrome (ALMS), a multi-systemic ciliopathy characterised by neurosensory deficits, metabolic disorders, and multi-organ fibrosis. To better understand the tissue-dependent role of ALMS1, we utilised CRISPR/Cas9 technology to develop a zebrafish model with alms1 depletion. Multi-tissue transcriptomic profiling revealed that alms1 depletion has pleiotropic effects on gene expression, with the brain and eyes displaying the most pronounced transcriptomic alterations, including disrupted ciliary function and immune dysregulation. Inflammatory and innate immune pathways along with glutamatergic synapse-related processes were significantly affected in the brain and eyes but with different gene expression signatures. The analysis further highlights tissue-specific processes, primarily associated with organ dysfunction. Additionally, our findings underscore the role of alms1 in regulating age-associated gene expression profiles in the brain, suggesting a link between ciliary dysfunction and accelerated brain ageing. Comparative analyses with Bardet-Biedl Syndrome iPSC models revealed shared pathways, reinforcing the potential of ciliopathies as models for ageing-related disorders. This study provides novel insights into the tissue-specific functions of alms1 and the molecular mechanisms underlying ALMS, paving the way for the development of targeted therapeutic strategies.

DHX15 is an ATP-dependent RNA helicase involved in pre-mRNA splicing and a downstream substrate for Akt1, which plays a significant role in vascular biology. The aim of this study was to explore the regulatory function of DHX15 over the vasculature and endothelial cell biology. Results: DHX15-/- was lethal in mouse and zebrafish embryos. DHX15-/- zebrafish also showed an undeveloped parachordal line, which leads to the formation of lymphatic structures. DHX15+/- mice triggered lower vascular network density and impaired lymphatic function postnatally. Transcriptome and proteome analysis of DHX15 silenced LEC revealed alterations in the glycolysis and gluconeogenesis pathways. The validation of these results demonstrated an uncoupling of the glycolysis with the oxidation of pyruvate in the mitochondria and a lower activity of the Complex I, resulting in lower cellular ATP production. Noteworthy, DHX15+/- mice partially inhibited primary tumor growth and reduced lung metastasis after injection of LLC1 tumor cells.

IntroductionCalpain 3 is one of the calpain protease family members, which is a calcium-dependent proteolytic enzyme predominantly expressed in skeletal muscle. Loss-of-function mutations in the Calpain 3 gene have been related to autosomal recessive Limb-Girdle Muscular Dystrophy 1 (LGMDR1), a common form of muscular dystrophy. Recently, the heterozygous 21-bp deletion mutation of the Calpain 3 gene has been reported to cause autosomal dominant Limb-Girdle Muscular Dystrophy 4 (LGMDD4). According to its dominant inheritance pattern, it has been suggested that the deletion mutant proteins act in a dominant-negative manner. Therefore, we examined whether the mutant protein can suppress the activity of wild-type Calpain 3 and has any dominant toxicity in cell culture and in vivo Drosophila models. MethodsA human cell culture (HeLa cells) model with the transient transfection of human wild-type and mutant Calpain 3 and in vivo Drosophila models overexpressing wild-type and mutant Drosophila Calpain A and B were utilized in this study to assess dominant effects of Calpain 3 21-bp deletion mutant. Western blot analysis was used to determine protein stability and catalytic activity in cell culture. External eye morphology and muscle integrity were examined to observe dominant toxicity in Drosophila models. ResultsThe 21-bp deletion mutation of Calpain 3 resulted in catalytic inactivation, which did not inhibit wild-type Calpain 3 autolytic and catalytic activity against Calpastatin in HeLa cells. In addition, the mutant protein was normally processed by wild-type Calpain 3. Overexpression of wild-type and deletion mutant Calpain 3 in the Drosophila eye and muscles did not exhibit significant developmental and age-related dominant toxicity. DiscussionWe provide evidence that mutant Calpain 3 does not suppress wild-type Calpain 3 activity. Rather, it is a mutant lacking autocatalytic processing activity like many other loss-of-function Calpain 3 mutants causing LGMDR1. Our results implicate that the stability of the heteromeric mutant and wild-type Calpain 3 complexes may be affected without inhibiting the wild-type activity per se. However, a more thorough investigation is necessary to understand the molecular mechanism and dominant inheritance of the heterozygous 21-bp deletion mutation in LGMDD4.

Alzheimers Disease (AD) and Type 2 Diabetes (T2D) share a common hallmark of insulin resistance. Besides Insulin Receptor (IR), two non-canonical RTKs, ALK and RYK, exhibit significant and consistent functional downregulation in post-mortem AD and T2D tissues. Incidentally, both have Grb2 as a common downstream adapter and NOX4 as a common ROS producing factor. Here we show that Grb2 and NOX4 play critical roles in reducing the severity of both the diseases. The study demonstrates that the abundance of Grb2 in degenerative conditions, in conjunction with NOX4, reverse cytoskeletal degradation by counterbalancing the network of small GTPases. PAX4, a transcription factor for both Grb2 and NOX4, emerges as the key link between the common pathways of AD and T2D. Both ALK and RYK downregulation elevate the PAX4 level by reducing its suppressor ARX via Wnt/{beta}-Catenin signaling pathway. For the first time, this study brings together RTKs other than Insulin Receptor (IR), their common transcription factor PAX4 and both AD and T2D pathologies on a common regulatory platform.

High myopia (HM) and posterior staphyloma (PS) are major causes of vision loss worldwide. Genetic and environmental factors, especially light exposure, contribute to myopia. Mutations in low-density lipoprotein-related receptor type 2, LRP2 cause syndromic myopia, and the Foxg1-Cre-Lrp2lox/lox mouse is a model for myopia and PS but the involvement of LRP2 in non-syndromic HM (NSHM) was unknown. We showed that LRP2 levels were decreased in the vitreous of 25 patients with NSHM and PS, and that in human donor eyes affected by PS, LRP2 expression was reduced in the neural retina and retinal pigment epithelium (RPE). The morphologic changes of these RPE were similar to those observed in the RPE of the Foxg1- Cre-Lrp2lox/lox mouse. In iPSc-derived human RPE cells (iRPE), LRP2 was expressed at a functional location, and LRP2 silencing by a specific siRNA regulated genes belonging to pathways involved in eye and neuronal development, visual perception, tissue remodeling, hormone metabolism and RPE structure, demonstrating that LRP2 orchestrates in RPE, functions that are essential for eye growth. Exposure of iRPE to light with LEDs of different wavelengths upregulated LRP2 expression, with higher efficacy for red light. Conversely, LRP2 expression was downregulated after cortisol exposure. Our findings link LRP2 to myopization and environmental factors and highlight its role in NSHM and PS in humans. LRP2 appears to be a viable target for interventional strategies in the treatment of NSHM. One Sentence SummaryLRP2, pivotal in the regulation of eye growth, exhibits a decrease in high myopic eyes. Its expression is augmented by light exposure in retinal pigment epithelial cells.

The accumulation of the age pigment lipofuscin within the retinal pigment epithelium (RPE) is one the most remarkable changes observed in association with age-related macular degeneration (AMD) and Stargardt disease. Both aging and pathological processes lead to the accumulation of melanolipofuscin (MLF) granules, which have been reported to reflect the onset of AMD more accurately than lipofuscin. The underlying mechanism by which MLF forms is still not understood. We investigate the potential role that melanin plays in the degradation of lipofuscin and MLF in pigmented Abca4-/- mice following treatment with several NO generating drugs. Abca4-/- mice are generally used as models for lipofuscin-related eye diseases. We also induced melanogenesis in albino Abca4-/- mice via the over-expression of tyrosinase, the key enzyme involved in melanogenesis. We compared the ultrastructure of lipofuscinogensis in the RPE of pigmented and albino Abca4-/- mice. Fluorescence microscopy was employed for the quantification of lipofuscin. We found high amounts of unique thin (3-4 nm) lamellar membranes (TLMs) that were left over from the degradation of photoreceptor disc membranes by high-resolution electron microscopy. Accumulated TLMs were significantly more frequent in the RPE cells of the albinos than the pigmented mice, indicating that melanin plays a role in removing TLMs. The intravitreal injection of several NO generating drugs was found to reduce the amount of autofluorescent lipofuscin in the cytoplasm of RPE cells, particularly the MLF granules of pigmented Abca4-/- mice. No effect was observed in terms of lipofuscin removal in NO-exposed albino Abca4-/- mice. However, transfection with tyrosinase led to a reduction in the lipofuscin levels of artificially pigmented RPE cells in albino Abca4-/- mice following the formation of melanin. The results show for the first time that melanin plays an important, if not a key, role in the degradation of lipofuscin in RPE cells.

Okur-Chung Neurodevelopmental Syndrome (OCNDS) is a rare, autosomal dominant disorder caused by heterozygous pathogenic variants in the CSNK2A1 gene. CSNK2A1 encodes the subunit of protein kinase CK2, involved in diverse biological processes. In 2016, Okur et al. reported the discovery of germline de novo missense and canonical splice site mutations in CSNK2A1 in five female patients with OCNDS. The syndrome is characterized by developmental delays, intellectual disability, hypotonia, feeding difficulties, dysmorphic facial features, and disrupted circadian rhythms, leading to sleep disturbances. The complex phenotypic spectrum of OCNDS underscores the need for robust model systems to investigate genotype-phenotype correlations, disease mechanisms, and potential therapies. In this study, we employed an overexpression strategy in a zebrafish model to investigate the functional consequences of select CSNK2A1 variants implicated in OCNDS. Our findings revealed distinct morphological phenotypes resulting from the overexpression of different CSNK2A1 mutants, indicating a direct correlation between genetic alterations and phenotypic manifestations. Notably, the CSNK2A1 p.Arg191Ter (R191X) mutation had a significant impact on the phenotype. Co-injection of wild-type CSNK2A1 mRNA with mutant CSNK2A1 mRNA rescued morphological abnormalities in zebrafish embryos. Overall our study highlights the utility of zebrafish as an adaptable model system for examining the functional impact of CSNK2A1 mutations and exploring novel therapeutic avenues.

Marked accumulation of mitochondrial DNA (mtDNA) with a particular pathogenic mutation is necessary for the mutant mtDNA to express its pathogenicity as mitochondrial respiration defects. However, the nuclear genome background, or the physiological status, or both, might also be important for the pathogenic regulation of mutant mtDNAs, because most mitochondrial function is controlled by polypeptides encoded in the nuclear genome. To test this, we generated diabetic mice carrying pathogenic mtDNA with a large-scale deletion ({Delta}mtDNA) that loses six tRNA genes and seven structural genes essential for mitochondrial respiration. Compared with non-diabetic mice carrying {Delta}mtDNA, diabetic mice carrying {Delta}mtDNA showed a decrease in mitochondrial biogenesis regulated by nuclear-encoded genes, and mitochondrial respiration defects and the resultant mitochondrial disease phenotypes were induced even in the case of low loads of {Delta}mtDNA. In addition, diabetic culture conditions intensified the pathogenicity of human mtDNA with an A3243G point mutation in the tRNALue (UUR) gene. Our results indicated that the diabetic conditions are a modifier that exacerbates mitochondrial respiration defects due to mutant mtDNAs. The finding suggests the possibility that recovery from diabetic conditions might be an effective treatment strategy for some disorders involving both mutant mtDNAs and diabetic signs.\n\nAuthor SummaryIt has been reported that accumulation of pathogenic mutant mitochondrial DNA (mtDNA) and the resultant mitochondrial metabolic dysfunction are associated with a wide variety of disorders, such as mitochondrial diseases, diabetes, neuo-degenerative disorders, and cancers. Considering that most mitochondrial function is regulated by nuclear-genome-encoded polypeptides, it is very important to focus on cooperation between mutant mtDNA, nuclear genetic background, and vital conditions for understanding precise pathogeneses of mtDNA-mediated disorders. By using model cells and mice carrying pathogenic mtDNAs, we report here that diabetic conditions are a modifier for the pathogenic regulation of mutant mtDNAs. Because the onset and progression of diabetes are often associated with aging, our finding suggests that some age-associated disorders with mutant mtDNAs and diabetic complications might be induced partly by enhancement of the pathogenicity of mutant mtDNAs by diabetic conditions.

This discourse probes the mechanistic molecular details of butyrate action in maintaining host-cholesterol balance. Hepatic miR122 being the most indispensable regulator of cholesterol metabolic enzymes, we studied upstream players of miR122 biogenesis in the presence and absence of butyrate in Huh7 cells and mice model. We showed that butyrate treatment caused upregulation of RNA-binding protein, AUF-1 resulting in RNase-III nuclease, Dicer-1 instability, and significant diminution of miR122. We proved its importance of AUF-1 and sequential downstream players in AUF-1-knock-down mice. We synthesized unique self-transfecting GMO (guanidinium-morpholino-oligonucleotides) linked PMO (Phosphorodiamidate-Morpholino Oligonucleotides)-based antisense reagent and injection of which in mouse caused near absence of AUF-1 coupled with increased Dicer-1 and miR122, and reduced serum cholesterol regardless of butyrate treatment indicating that butyrate acts though AUF-1. The roster of intracellular players was as follows: AUF-1-Dicer-1-miR122 for triggering butyrate driven hypocholesterlaemia. To our knowledge this is the first report linking AUF-1 with cholesterol biogenesis.

The prevalence of non-alcohol fatty liver disease (NAFLD), defined as the livers excessive fat accumulation, continues to increase dramatically. We have recently revealed the molecular mechanism underlying NAFLD using in-depth multi-omics profiling and identified that combined metabolic activators (CMA) could be administered to decrease the amount of hepatic steatosis (HS) in mouse model and NAFLD patients based on systems analysis. Here, we investigated the effects of a CMA including L-carnitine, N-acetyl-l-cysteine, nicotinamide riboside and betaine on a Golden Syrian hamster NAFLD model fed with HFD, and found that HS was decreased with the administration of CMA. To explore the mechanisms involved in the clearance HS, we generated liver transcriptomics data before and after CMA administration, and integrated these data using liver-specific genome-scale metabolic model of liver tissue. We systemically determined the molecular changes after the supplementation of CMAs and found that it activates mitochondria in the liver tissue by modulating the global fatty acid, amino acids, antioxidant and folate metabolism.

Molecular and cellular mechanisms of mutations of splicing factors in heart function are not well understood. The splicing of precursor mRNA is dependent on an essential group of splicing factors containing serine-arginine (SR) domain(s) that are critical for protein-RNA and protein-protein interaction in the spliceosome assembly. Phosphorylation of SR domains plays a key role in splicing control and the distribution of splicing factors in the cell. RNA binding motif 20 (RBM20) is a splicing factor predominantly expressed in muscle tissues with the highest expression level in the heart. However, its phosphorylation status is completely unknown up-to-date. In this study, we identified sixteen amino acid residues that are phosphorylated by middle-down mass spectrometry. Four of them are located in the SR domain, and two out of the four residues, S638 and S640, play an essential role in splicing control and facilitate RBM20 shuttling from the nucleus to the cytoplasm. Re-localization of RBM20 promotes protein aggregation in the cytoplasm. We have also verified that SR-protein kinases (SRPKs), cdc2-like kinases (CLKs) and protein kinase B (PKB or AKT) phosphorylate S638 and S640. Mutations of S638A and S640G reduce RBM20 phosphorylation and disrupt the splicing. Taken together, we determine the phosphorylation status of RBM20 and provide the first evidence that phosphorylation on SR domain is crucial for pre-mRNA splicing and protein trafficking. Our findings reveal a new role of RBM20 via protein shuttling in cardiac function.

Dehydrogenase/reductase (SDR family) member1, DHRS1, a member of the conserved short chain dehydrogenase/reductase (SDR) superfamily, has been identified in lipid droplets proteome of different cells and tissues. However, until now, little is known about the potential role of DHRS1 on the lipid droplet (LD). Here, we report that DHRS1 localized to the lipid droplet in Huh7 and HeLa cells and ectopic expression of DHRS1 in HeLa cell induced a significant change in the lipid droplet morphology resulting in nearly 2 fold increase both in lipid droplet size and total triacylglycerol level independent of oleic acid treatment. DHRS1 interacted with ERLIN1, a non-caveolae lipid raft-like domain marker, in HeLa cell and ERLIN1 deficient HeLa cells displayed no detectable change in LD morphology. Although ectopic expression of DHRS1-GFP fusion protein in ERLIN1 deficient HeLa cells resulted in fewer GFP-labeled ring structures relative to WT HeLa cell; thus suggesting that ERLIN1 may be involved in regulating DHRS1 protein turnover. Taken together, these data showed that DHRS1 localized to the LD and induced a significant change in LD morphology which may be regulated by ERLIN1.

Understanding the early stages of human congenital myopathies is critical for proposing strategies for improving skeletal muscle performance by the functional integrity of cytoskeleton. SH3 and cysteine-rich domain 3 (Stac3) is a protein involved in nutrient sensing, and is an essential component of the excitation-contraction (EC) coupling machinery for Ca2+ releasing. A mutation in STAC3 causes debilitating Native American myopathy (NAM) in humans, and loss of this gene in mice and zebrafish resulted in death in early life. Previously, NAM patients demonstrated increased lipids in skeletal muscle biopsy. However, elevated neutral lipids could alter muscle function in NAM disease via EC coupling apparatus is yet undiscovered in early development. Here, using a CRISPR/Cas9 induced stac3 knockout (KO) zebrafish model, we determined that loss of stac3 led to muscle weakness, as evidenced by delayed larval hatching. We observed decreased whole-body Ca2+ level at 5 days post-fertilization (dpf) and defects in the skeletal muscle cytoskeleton, i.e., F-actin and slow muscle fibers at 5 and 7 dpf. Homozygous larvae exhibited elevated neutral lipid levels at 5 dpf, which persisted beyond 7 dpf. Myogenesis regulators such as myoD and myf5, were significantly altered in stac3-/- larvae at 5 dpf, thus a progressive death of the KO larva by 11 dpf. In summary, the presented findings suggest that stac3-/- can serve as a non-mammalian model to identify lipid-lowering molecules for refining muscle function in NAM patients.

Marfan syndrome (MFS) is a connective tissue disorder characterized by long bone overgrowth, enlargement of the aorta, ocular anomalies and other symptoms. Current treatment focuses on managing aortic aneurysms to avoid dissection or rupture. However, no cures are available. MFS is caused by one of >1,800 dominant pathogenic variants in FBN1, which encodes the extracellular matrix (ECM) protein fibrillin-1. A significant number of FBN1 variants result in premature termination codons (PTCs). Recently, small molecules were identified that can promote translational readthrough of PTCs and were evaluated in preclinical and clinical trials for several genetic disorders. Here, we show that the translational readthrough drugs ataluren and gentamicin ameliorated FBN1 deposition in some MFS patient-derived skin fibroblast lines harboring PTC variants in FBN1. In contrast, inhibitors of NMD were cytotoxic to the skin fibroblast lines that we analyzed. We conclude that promoting translational readthrough of PTC variants in FBN1 could result in a therapeutic benefit for MFS patients with specific PTCs in FBN1 and that its efficacy will likely depend on the PTC sequence context, the amino acids that are incorporated in FBN1 after PTC suppression and the overall increase of FBN1 deposition in the ECM.