A crucial role of mitochondrial Hsp40 in preventing dilated cardiomyopathy

Mitochondrial Dysfunction: A Roadmap for Understanding and Tackling Cardiovascular Aging

Cardiovascular aging is a progressive remodeling process constituting a variety of cellular and molecular alterations that are closely linked to mitochondrial dysfunction. Therefore, gaining a deeper understanding of the changes in mitochondrial function during cardiovascular aging is crucial for preventing cardiovascular diseases. Cardiac aging is accompanied by fibrosis, cardiomyocyte hypertrophy, metabolic changes, and infiltration of immune cells, collectively contributing to the overall remodeling of the heart. Similarly, during vascular aging, there is a profound remodeling of blood vessel structure. These remodeling present damage to endothelial cells, increased vascular stiffness, impaired formation of new blood vessels (angiogenesis), the development of arteriosclerosis, and chronic vascular inflammation. This review underscores the role of mitochondrial dysfunction in cardiac aging, exploring its impact on fibrosis and myocardial alterations, metabolic remodeling, immune response remodeling, as well as in vascular aging in the heart. Additionally, we emphasize the significance of mitochondria-targeted therapies in preventing cardiovascular diseases in the elderly.

DNAJA3 regulates B cell development and immune function

BACKGROUND

DnaJ homolog subfamily A member 3 (DNAJA3), also known as the tumorous imaginal disc (Tid1), is shown to be crucial in T cell development. DNAJA3 functions as a tumor suppressor implicated in lymphocyte development and survival. However, the role of DNAJA3 in B cell development and immune function remains unknown. In this study, we utilized a mouse model of B cell-specific DNAJA3 knockout (CD19-Cre/+; DNAJA3flx/flx) to investigate the physiological function of DNAJA3 in B cell development and immune function.

METHODS

We characterized B cell populations in various developmental stages and examined mitochondrial content and function between control and DNAJA3 KO using flow cytometry analysis. DNAJA3 and OXPHOS protein complexes in sorted B cells between mice groups were compared using immunoblot techniques. The activity of B cell blastogenesis in splenocytes was measured by performing CFSE and MTT assays. Furthermore, immunoglobulin production was detected using the ELISA method.

RESULTS

DNAJA3 deficiency decreases from pro B cells to immature B cells. The overall B220+ population in the bone marrow and secondary immune organs also decreased. B cell subpopulations B1 (B1b) and B2 significantly decrease. The B cell blastogenesis activity and immunoglobulin production decreased in DNAJA3 KO mice. Mechanistically, DNAJA3 deficiency significantly increases dysfunctional mitochondria activity and decreases mitochondrial mass, membrane potential, and mitochondria respiratory complex proteins. These factors could have influenced B cell differentiation during development, differentiation to antibody-secreting cells, and immune activation.

CONCLUSION

Overall, our study provides supportive evidence for the role of DNAJA3 in B cell development and function.

A peptide derived from TID1S rescues frataxin deficiency and mitochondrial defects in FRDA cellular models

Friedreich's ataxia (FRDA), the most common recessive inherited ataxia, results from homozygous guanine-adenine-adenine (GAA) repeat expansions in intron 1 of the FXN gene, which leads to the deficiency of frataxin, a mitochondrial protein essential for iron-sulphur cluster synthesis. The study of frataxin protein regulation might yield new approaches for FRDA treatment. Here, we report tumorous imaginal disc 1 (TID1), a mitochondrial J-protein cochaperone, as a binding partner of frataxin that negatively controls frataxin protein levels. TID1 interacts with frataxin both in vivo in mouse cortex and in vitro in cortical neurons. Acute and subacute depletion of frataxin using RNA interference markedly increases TID1 protein levels in multiple cell types. In addition, TID1 overexpression significantly increases frataxin precursor but decreases intermediate and mature frataxin levels in HEK293 cells. In primary cultured human skin fibroblasts, overexpression of TID1S results in decreased levels of mature frataxin and increased fragmentation of mitochondria. This effect is mediated by the last 6 amino acids of TID1S as a peptide made from this sequence rescues frataxin deficiency and mitochondrial defects in FRDA patient-derived cells. Our findings show that TID1 negatively modulates frataxin levels, and thereby suggests a novel therapeutic target for treating FRDA.

A genetic basis of mitochondrial DNAJA3 in nonalcoholic steatohepatitis-related hepatocellular carcinoma

BACKGROUND AND AIMS

NAFLD is the most common form of liver disease worldwide, but only a subset of individuals with NAFLD may progress to NASH. While NASH is an important etiology of HCC, the underlying mechanisms responsible for the conversion of NAFLD to NASH and then to HCC are poorly understood. We aimed to identify genetic risk genes that drive NASH and NASH-related HCC.

APPROACH AND RESULTS

We searched genetic alleles among the 24 most significant alleles associated with body fat distribution from a genome-wide association study of 344,369 individuals and validated the top allele in 3 independent cohorts of American and European patients (N=1380) with NAFLD/NASH/HCC. We identified an rs3747579-TT variant significantly associated with NASH-related HCC and demonstrated that rs3747579 is expression quantitative trait loci of a mitochondrial DnaJ Heat Shock Protein Family (Hsp40) Member A3 ( DNAJA3 ). We also found that rs3747579-TT and a previously identified PNPLA3 as a functional variant of NAFLD to have significant additional interactions with NASH/HCC risk. Patients with HCC with rs3747579-TT had a reduced expression of DNAJA3 and had an unfavorable prognosis. Furthermore, mice with hepatocyte-specific Dnaja3 depletion developed NASH-dependent HCC either spontaneously under a normal diet or enhanced by diethylnitrosamine. Dnaja3 -deficient mice developed NASH/HCC characterized by significant mitochondrial dysfunction, which was accompanied by excessive lipid accumulation and inflammatory responses. The molecular features of NASH/HCC in the Dnaja3 -deficient mice were closely associated with human NASH/HCC.

CONCLUSIONS

We uncovered a genetic basis of DNAJA3 as a key player of NASH-related HCC.

Multiple solutions at the genomic level in response to selective breeding for high locomotor activity

Replicate lines under uniform selection often evolve in different ways. Previously, analyses using whole-genome sequence data for individual mice (Mus musculus) from 4 replicate High Runner lines and 4 nonselected control lines demonstrated genomic regions that have responded consistently to selection for voluntary wheel-running behavior. Here, we ask whether the High Runner lines have evolved differently from each other, even though they reached selection limits at similar levels. We focus on 1 High Runner line (HR3) that became fixed for a mutation at a gene of major effect (Myh4Minimsc) that, in the homozygous condition, causes a 50% reduction in hindlimb muscle mass and many pleiotropic effects. We excluded HR3 from SNP analyses and identified 19 regions not consistently identified in analyses with all 4 lines. Repeating analyses while dropping each of the other High Runner lines identified 12, 8, and 6 such regions. (Of these 45 regions, 37 were unique.) These results suggest that each High Runner line indeed responded to selection somewhat uniquely, but also that HR3 is the most distinct. We then applied 2 additional analytical approaches when dropping HR3 only (based on haplotypes and nonstatistical tests involving fixation patterns). All 3 approaches identified 7 new regions (as compared with analyses using all 4 High Runner lines) that include genes associated with activity levels, dopamine signaling, hippocampus morphology, heart size, and body size, all of which differ between High Runner and control lines. Our results illustrate how multiple solutions and "private" alleles can obscure general signatures of selection involving "public" alleles.

Heat shock proteins: Biological functions, pathological roles, and therapeutic opportunities

The heat shock proteins (HSPs) are ubiquitous and conserved protein families in both prokaryotic and eukaryotic organisms, and they maintain cellular proteostasis and protect cells from stresses. HSP protein families are classified based on their molecular weights, mainly including large HSPs, HSP90, HSP70, HSP60, HSP40, and small HSPs. They function as molecular chaperons in cells and work as an integrated network, participating in the folding of newly synthesized polypeptides, refolding metastable proteins, protein complex assembly, dissociating protein aggregate dissociation, and the degradation of misfolded proteins. In addition to their chaperone functions, they also play important roles in cell signaling transduction, cell cycle, and apoptosis regulation. Therefore, malfunction of HSPs is related with many diseases, including cancers, neurodegeneration, and other diseases. In this review, we describe the current understandings about the molecular mechanisms of the major HSP families including HSP90/HSP70/HSP60/HSP110 and small HSPs, how the HSPs keep the protein proteostasis and response to stresses, and we also discuss their roles in diseases and the recent exploration of HSP related therapy and diagnosis to modulate diseases. These research advances offer new prospects of HSPs as potential targets for therapeutic intervention.

Putting human Tid-1 in context: an insight into its role in the cell and in different disease states

Background

Tumorous imaginal disc 1 (hTid-1) or DnaJ homolog subfamily A member 3 (DNAJA3), is a part of the heat shock protein (Hsp) 40 family and is predominantly found to reside in the mitochondria. hTid-1 has two mRNA splicing variants, hTid-1S and hTid-1L of 40 and 43 kDa respectively in the cytosol which are later processed upon import into the mitochondrial matrix. hTid-1 protein is a part of the DnaJ family of proteins which are co-chaperones and specificity factors for DnaK proteins of the Hsp70 family, and bind to Hsp70, thereby activating its ATPase activity. hTid-1 has been found to be critical for a lot of important cellular processes such as proliferation, differentiation, growth, survival, senescence, apoptosis, and movement and plays key roles in the embryo and skeletal muscle development.

Main body

hTid-1 participates in several protein–protein interactions in the cell, which mediate different processes such as proteasomal degradation and autophagy of the interacting protein partners. hTid-1 also functions as a co-chaperone and participates in interactions with several different viral oncoproteins. hTid-1 also plays a critical role in different human diseases such as different cancers, cardiomyopathies, and neurodegenerative disorders.

Conclusion

This review article is the first of its kind presenting consolidated information on the research findings of hTid-1 to date. This review suggests that the current knowledge of the role of hTid-1 in disorders like cancers, cardiomyopathies, and neurodegenerative diseases can be correlated with the findings of its protein–protein interactions that can provide a deep insight into the pathways by which hTid-1 affects disease pathogenesis and it can be stated that hTid-1 may serve as an important therapeutic target for these disorders.

Graphical Abstract

Gut microbiota production of trimethyl-5-aminovaleric acid reduces fatty acid oxidation and accelerates cardiac hypertrophy

Numerous studies found intestinal microbiota alterations which are thought to affect the development of various diseases through the production of gut-derived metabolites. However, the specific metabolites and their pathophysiological contribution to cardiac hypertrophy or heart failure progression still remain unclear. N,N,N-trimethyl-5-aminovaleric acid (TMAVA), derived from trimethyllysine through the gut microbiota, was elevated with gradually increased risk of cardiac mortality and transplantation in a prospective heart failure cohort (n = 1647). TMAVA treatment aggravated cardiac hypertrophy and dysfunction in high-fat diet-fed mice. Decreased fatty acid oxidation (FAO) is a hallmark of metabolic reprogramming in the diseased heart and contributes to impaired myocardial energetics and contractile dysfunction. Proteomics uncovered that TMAVA disturbed cardiac energy metabolism, leading to inhibition of FAO and myocardial lipid accumulation. TMAVA treatment altered mitochondrial ultrastructure, respiration and FAO and inhibited carnitine metabolism. Mice with γ-butyrobetaine hydroxylase (BBOX) deficiency displayed a similar cardiac hypertrophy phenotype, indicating that TMAVA functions through BBOX. Finally, exogenous carnitine supplementation reversed TMAVA induced cardiac hypertrophy. These data suggest that the gut microbiota-derived TMAVA is a key determinant for the development of cardiac hypertrophy through inhibition of carnitine synthesis and subsequent FAO.

Intestinal microbiota alterations may affect heart function through the production of gut-derived metabolites. Here the authors found that gut microbiota-derived TMAVA is a key determinant for the development of cardiac hypertrophy through inhibition of carnitine synthesis and subsequent fatty acid oxidation.

Regulation of p53 and Cancer Signaling by Heat Shock Protein 40/J-Domain Protein Family Members

Heat shock proteins (HSPs) are molecular chaperones that assist diverse cellular activities including protein folding, intracellular transportation, assembly or disassembly of protein complexes, and stabilization or degradation of misfolded or aggregated proteins. HSP40, also known as J-domain proteins (JDPs), is the largest family with over fifty members and contains highly conserved J domains responsible for binding to HSP70 and stimulation of the ATPase activity as a co-chaperone. Tumor suppressor p53 (p53), the most frequently mutated gene in human cancers, is one of the proteins that functionally interact with HSP40/JDPs. The majority of p53 mutations are missense mutations, resulting in acquirement of unexpected oncogenic activities, referred to as gain of function (GOF), in addition to loss of the tumor suppressive function. Moreover, stability and levels of wild-type p53 (wtp53) and mutant p53 (mutp53) are crucial for their tumor suppressive and oncogenic activities, respectively. However, the regulatory mechanisms of wtp53 and mutp53 are not fully understood. Accumulating reports demonstrate regulation of wtp53 and mutp53 levels and/or activities by HSP40/JDPs. Here, we summarize updated knowledge related to the link of HSP40/JDPs with p53 and cancer signaling to improve our understanding of the regulation of tumor suppressive wtp53 and oncogenic mutp53 GOF activities.

Mitochondrial "dysmorphology" in variant classification

Mitochondrial disorders are challenging to diagnose. Exome sequencing has greatly enhanced the diagnostic precision of these disorders although interpreting variants of uncertain significance (VUS) remains a formidable obstacle. Whether specific mitochondrial morphological changes can aid in the classification of these variants is unknown. Here, we describe two families (four patients), each with a VUS in a gene known to affect the morphology of mitochondria through a specific role in the fission-fusion balance. In the first, the missense variant in MFF, encoding a fission factor, was associated with impaired fission giving rise to a characteristically over-tubular appearance of mitochondria. In the second, the missense variant in DNAJA3, which has no listed OMIM phenotype, was associated with fragmented appearance of mitochondria consistent with its published deficiency states. In both instances, the highly specific phenotypes allowed us to upgrade the classification of the variants. Our results suggest that, in select cases, mitochondrial "dysmorphology" can be helpful in interpreting variants to reach a molecular diagnosis.

Heat Shock Proteins: Connectors between Heart and Kidney

Over the development of eukaryotic cells, intrinsic mechanisms have been developed in order to provide the ability to defend against aggressive agents. In this sense, a group of proteins plays a crucial role in controlling the production of several proteins, guaranteeing cell survival. The heat shock proteins (HSPs), are a family of proteins that have been linked to different cellular functions, being activated under conditions of cellular stress, not only imposed by thermal variation but also toxins, radiation, infectious agents, hypoxia, etc. Regarding pathological situations as seen in cardiorenal syndrome (CRS), HSPs have been shown to be important mediators involved in the control of gene transcription and intracellular signaling, in addition to be an important connector with the immune system. CRS is classified as acute or chronic and according to the first organ to suffer the injury, which can be the heart (CRS type 1 and type 2), kidneys (CRS type 3 and 4) or both (CRS type 5). In all types of CRS, the immune system, redox balance, mitochondrial dysfunction, and tissue remodeling have been the subject of numerous studies in the literature in order to elucidate mechanisms and propose new therapeutic strategies. In this sense, HSPs have been targeted by researchers as important connectors between kidney and heart. Thus, the present review has a focus to present the state of the art regarding the role of HSPs in the pathophysiology of cardiac and renal alterations, as well their role in the kidney–heart axis.

Mitochondrial HSP70 Chaperone System-The Influence of Post-Translational Modifications and Involvement in Human Diseases

Since their discovery, heat shock proteins (HSPs) have been identified in all domains of life, which demonstrates their importance and conserved functional role in maintaining protein homeostasis. Mitochondria possess several members of the major HSP sub-families that perform essential tasks for keeping the organelle in a fully functional and healthy state. In humans, the mitochondrial HSP70 chaperone system comprises a central molecular chaperone, mtHSP70 or mortalin (HSPA9), which is actively involved in stabilizing and importing nuclear gene products and in refolding mitochondrial precursor proteins, and three co-chaperones (HSP70-escort protein 1-HEP1, tumorous imaginal disc protein 1-TID-1, and Gro-P like protein E-GRPE), which regulate and accelerate its protein folding functions. In this review, we summarize the roles of mitochondrial molecular chaperones with particular focus on the human mtHsp70 and its co-chaperones, whose deregulated expression, mutations, and post-translational modifications are often considered to be the main cause of neurological disorders, genetic diseases, and malignant growth.

Heat Shock Proteins: Potential Modulators and Candidate Biomarkers of Peripartum Cardiomyopathy

Peripartum cardiomyopathy (PPCM) is a potentially life-threatening condition in which heart failure and systolic dysfunction occur late in pregnancy or within months following delivery. To date, no reliable biomarkers or therapeutic interventions for the condition exist, thus necessitating an urgent need for identification of novel PPCM drug targets and candidate biomarkers. Leads for novel treatments and biomarkers are therefore being investigated worldwide. Pregnancy is generally accompanied by dramatic hemodynamic changes, including a reduced afterload and a 50% increase in cardiac output. These increased cardiac stresses during pregnancy potentially impair protein folding processes within the cardiac tissue. The accumulation of misfolded proteins results in increased toxicity and cardiac insults that trigger heart failure. Under stress conditions, molecular chaperones such as heat shock proteins (Hsps) play crucial roles in maintaining cellular proteostasis. Here, we critically assess the potential role of Hsps in PPCM. We further predict specific associations between the Hsp types Hsp70, Hsp90 and small Hsps with several proteins implicated in PPCM pathophysiology. Furthermore, we explore the possibility of select Hsps as novel candidate PPCM biomarkers and drug targets. A better understanding of how these Hsps modulate PPCM pathogenesis holds promise in improving treatment, prognosis and management of the condition, and possibly other forms of acute heart failure.

DNAJA3/Tid1 Is Required for Mitochondrial DNA Maintenance and Regulates Migration and Invasion of Human Gastric Cancer Cells

BACKGROUND

Gastric cancer is a common health issue. Deregulated cellular energetics is regarded as a cancer hallmark and mitochondrial dysfunction might contribute to cancer progression. Tid1, a mitochondrial co-chaperone, may play a role as a tumor suppressor in various cancers, but the role of Tid1 in gastric cancers remains under investigated.

METHODS

The clinical TCGA online database and immunohistochemical staining for Tid1 expression in tumor samples of gastric cancer patients were analyzed. Tid1 knockdown by siRNA was applied to investigate the role of Tid1 in gastric cancer cells.

RESULTS

Low Tid1 protein-expressing gastric cancer patients had a poorer prognosis and higher lymph node invasion than high Tid1-expressing patients. Knockdown of Tid1 did not increase cell proliferation, colony/tumor sphere formation, or chemotherapy resistance in gastric cancer cells. However, Tid1 knockdown increased cell migration and invasion. Moreover, Tid1 knockdown reduced the mtDNA copy number of gastric cancer cells. In addition, the Tid1-galectin-7-MMP-9 axis might be associated with Tid1 knockdown-induced cell migration and invasion of gastric cancer cells.

CONCLUSIONS

Tid1 is required for mtDNA maintenance and regulates migration and invasion of gastric cancer cells. Tid1 deletion may be a poor prognostic factor in gastric cancers and could be further investigated for development of gastric cancer treatments.

Genetic aspects of the oxidative phosphorylation dysfunction in dilated cardiomyopathy

Dilated cardiomyopathy is a frequent and extremely heterogeneous medical condition. Deficits in the oxidative phosphorylation system have been described in patients suffering from dilated cardiomyopathy. Hence, mutations in proteins related to this biochemical pathway could be etiological factors for some of these patients. Here, we review the clinical phenotypes of patients harboring pathological mutations in genes related to the oxidative phosphorylation system, either encoded in the mitochondrial or in the nuclear genome, presenting with dilated cardiomyopathy. In addition to the clinical heterogeneity of these patients, the large genetic heterogeneity has contributed to an improper allocation of pathogenicity for many candidate mutations. We suggest criteria to avoid incorrect assignment of pathogenicity to newly found mutations and discuss possible therapies targeting the oxidative phosphorylation function.

Evaluation of the Role of Human DNAJAs in the Response to Cytotoxic Chemotherapeutic Agents in a Yeast Model System

Heat-shock proteins (HSPs) play a crucial role in maintaining protein stability for cell survival during stress-induced insults. Overexpression of HSPs in cancer cells results in antiapoptotic activity contributing to cancer cell survival and restricting the efficacy of cytotoxic chemotherapy, which continues to play an important role in the treatment of many cancers, including triple-negative breast cancer (TNBC). First-line therapy for TNBC includes anthracycline antibiotics, which are associated with serious dose-dependent side effects and the development of resistance. We previously identified YDJ1, which encodes a heat-shock protein 40 (HSP40), as an important factor in the cellular response to anthracyclines in yeast, with mutants displaying over 100-fold increased sensitivity to doxorubicin. In humans, the DNAJA HSP40s are homologues of YDJ1. To determine the role of DNAJAs in the cellular response to cytotoxic drugs, we investigated their ability to rescue ydj1Δ mutants from exposure to chemotherapeutic agents. Our results indicate that DNAJA1 and DNAJA2 provide effective protection, while DNAJA3 and DNAJA4 did not. The level of complementation was also dependent on the agent used, with DNAJA1 and DNAJA2 rescuing the ydj1Δ strain from doxorubicin, cisplatin, and heat shock. DNAJA3 and DNAJA4 did not rescue the ydj1Δ strain and interfered with the cellular response to stress when expressed in wild type background. DNAJA1 and DNAJA2 protect the cell from proteotoxic damage caused by reactive oxygen species (ROS) and are not required for repair of DNA double-strand breaks. These data indicate that the DNAJAs play a role in the protection of cells from ROS-induced cytotoxic stress.

Ube2v1 Positively Regulates Protein Aggregation by Modulating Ubiquitin Proteasome System Performance Partially Through K63 Ubiquitination

RATIONALE

Compromised protein quality control can result in proteotoxic intracellular protein aggregates in the heart, leading to cardiac disease and heart failure. Defining the participants and understanding the underlying mechanisms of cardiac protein aggregation is critical for seeking therapeutic targets. We identified Ube2v1 (ubiquitin-conjugating enzyme E2 variant 1) in a genome-wide screen designed to identify novel effectors of the aggregation process. However, its role in the cardiomyocyte is undefined.

OBJECTIVE

To assess whether Ube2v1 regulates the protein aggregation caused by cardiomyocyte expression of a mutant αB crystallin (CryAB^R120G) and identify how Ube2v1 exerts its effect.

METHODS AND RESULTS

Neonatal rat ventricular cardiomyocytes were infected with adenoviruses expressing either wild-type CryAB (CryAB^WT) or CryAB^R120G. Subsequently, loss- and gain-of-function experiments were performed. Ube2v1 knockdown decreased aggregate accumulation caused by CryAB^R120G expression. Overexpressing Ube2v1 promoted aggregate formation in CryAB^WT and CryAB^R120G-expressing neonatal rat ventricular cardiomyocytes. Ubiquitin proteasome system performance was analyzed using a ubiquitin proteasome system reporter protein. Ube2v1 knockdown improved ubiquitin proteasome system performance and promoted the degradation of insoluble ubiquitinated proteins in CryAB^R120G cardiomyocytes but did not alter autophagic flux. Lys (K) 63-linked ubiquitination modulated by Ube2v1 expression enhanced protein aggregation and contributed to Ube2v1's function in regulating protein aggregate formation. Knocking out Ube2v1 exclusively in cardiomyocytes by using AAV9 (adeno-associated virus 9) to deliver multiplexed single guide RNAs against Ube2v1 in cardiac-specific Cas9 mice alleviated CryAB^R120G-induced protein aggregation, improved cardiac function, and prolonged lifespan in vivo.

CONCLUSIONS

Ube2v1 plays an important role in protein aggregate formation, partially by enhancing K63 ubiquitination during a proteotoxic stimulus. Inhibition of Ube2v1 decreases CryAB^R120G-induced aggregate formation through enhanced ubiquitin proteasome system performance rather than autophagy and may provide a novel therapeutic target to treat cardiac proteinopathies.

PreS1 Mutations Alter the Large HBsAg Antigenicity of a Hepatitis B Virus Strain Isolated in Bangladesh

Mutations in the hepatitis B virus (HBV) genome can potentially lead to vaccination failure, diagnostic escape, and disease progression. However, there are no reports on viral gene expression and large hepatitis B surface antigen (HBsAg) antigenicity alterations due to mutations in HBV isolated from a Bangladeshi population. Here, we sequenced the full genome of the HBV isolated from a clinically infected patient in Bangladesh. The open reading frames (ORFs) (P, S, C, and X) of the isolated HBV strain were successfully amplified and cloned into a mammalian expression vector. The HBV isolate was identified as genotype C (sub-genotype C2), serotype adr, and evolutionarily related to strains isolated in Indonesia, Malaysia, and China. Clinically significant mutations, such as preS1 C2964A, reverse transcriptase domain I91L, and small HBsAg N3S, were identified. The viral P, S, C, and X genes were expressed in HEK-293T and HepG2 cells by transient transfection with a native subcellular distribution pattern analyzed by immunofluorescence assay. Western blotting of large HBsAg using preS1 antibody showed no staining, and preS1 ELISA showed a significant reduction in reactivity due to amino acid mutations. This mutated preS1 sequence has been identified in several Asian countries. To our knowledge, this is the first report investigating changes in large HBsAg antigenicity due to preS1 mutations.

Tid1-S attenuates LPS-induced cardiac hypertrophy and apoptosis through ER-a mediated modulation of p-PI3K/p-Akt signaling cascade

Myocardial dysfunction is clinically relevant? repercussion that follows sepsis. Tid 1 protein has been implicated in many biological process. However, the role of Tid 1 in lipopolysaccharide (LPS)-induced cardiomyocyte hypertrophy and apoptosis remains elusive. In the current research endeavor, we have elucidated the role of Tid1-S on LPS-induced cardiac hypertrophy and apoptosis. Interestingly, we found that overexpression of Tid1-S suppressed TLR-4, NFATc3, and BNP protein expression which eventually led to inhibition of LPS-induced cardiac hypertrophy. Moreover, Tid1-S overexpression attenuated cellular apoptosis and activated survival proteins p-PI3K and p^ser473 Akt. Besides this, Tid1-S overexpression enhanced ER-a protein expression. Collectively, our data suggest that Tid1-S plausibly enhance ER-a protein and further activate p-PI3K and p ^ser473 Akt survival protein expression; which thereby led to attenuation of LPS-induced apoptosis in cardiomyoblast cells. Interestingly, our data suggest that Tid1-S is involved in attenuation of cardiomyoblast cells damages induced by LPS.

Satellite RNA Increases DNA Damage and Accelerates Tumor Formation in Mouse Models of Pancreatic Cancer

Highly repetitive tandem arrays such as satellite sequences in the centromeric and pericentromeric regions of chromosomes, which were previously considered to be silent, are actively transcribed in various biological processes, including cancers. In the pancreas, this aberrant expression occurs even in Kras-mutated pancreatic intraepithelial neoplasia (PanIN) tissues, which are precancerous lesions. To determine the biological role of satellite RNAs in carcinogenesis in vivo, we constructed mouse major satellite (MajSAT) RNA-expressing transgenic mice. However, these transgenic mice did not show spontaneous malignant tumor formation under normal breeding. Importantly, however, DNA damage was increased in pancreatic tissues induced by caerulein treatment or high-fat diet, which may be due to impaired nuclear localization of Y-Box Binding Protein 1 (YBX1), a component of the DNA damage repair machinery. In addition, when crossed with pancreas-specific Kras-mutant mice, MajSAT RNA expression resulted in an earlier increase in PanIN formation. These results suggest that aberrant MajSAT RNA expression accelerates oncogenesis by increasing the probability of a second driver mutation, thus accelerating cells to exit from the breakthrough phase to the expansion phase.Implications: Aberrant expression of satellite RNAs accelerates oncogenesis through a mechanism involving increased DNA damage. Mol Cancer Res; 16(8); 1255-62. ©2018 AACR.

Tumorous imaginal disc 1 (TID1) inhibits isoproterenol-induced cardiac hypertrophy and apoptosis by regulating c-terminus of hsc70-interacting protein (CHIP) mediated degradation of Gαs

Dilated cardiomyopathy (DCM) is the most common form of non-ischemic cardiomyopathy. It is characterized by ventricular chamber dilation, and myocyte hypertrophy. Human tumorous imaginal disc 1 (Tid1), a chaperone protein and response to regulate number of signaling molecules in the mitochondria or cytosol. Tid1 also plays a major role in preventing DCM; however, the role of Tid1 in isoproterenol (ISO)-induced cardiac apoptosis and hypertrophy remains unclear. H9c2 cells were pretreated Tid1 before ISO-induced hypertrophy and apoptosis and then evaluated by IHC, TUNEL assay, IFC, Co-IP, and Western blot. From the IHC experiment, we found that Tid1 proteins were increased in tissues from different stages of human myocardial infarction. Using H9c2 cardiomyoblast cells we found that Tid1 was decreased by ISO treatment. However, over-expression of Tid1S suppressed NFATc3, BNP and calcineurin protein expression and inhibited NFATc3 nuclear translocation in ISO induced cardiomyoblast cells. On the other hand, Tid1S over-expression activated survival proteins p-AKT^ser473 and decreased caspase-3 and cytochrome c expression. We also found that overexpression of Tid1 enhanced CHIP expression, and induced CHIP to ubiquitinate Gαs, resulting in increased Gαs degradation. Our study showed that Gαs is a novel substrate of CHIP, and we also found that the Tid1-CHIP complex plays an essential role in inhibiting ISO induced cardiomyoblast hypertrophy and apoptosis.

Differential expression of myocardial heat shock proteins in rats acutely exposed to fluoride

Acute fluoride (F-) toxicity is known to cause severe cardiac complications and leads to sudden heart failure. Previously, we reported that increased myocardial oxidative damage, apoptosis, altered cytoskeleton and AMPK signaling proteins associated with energy deprivation in acute F- induced cardiac dysfunction. The present study was aimed to decipher the status of myocardial heat shock proteins (Hsps-Hsp27, Hsp32, Hsp40, Hsp60, Hsp70, Hsp90) and heat shock transcription factor 1 (Hsf1) in acute F--intoxicated rats. In order to study the expression of myocardial Hsps, male Wistar rats were treated with single oral doses of 45 and 90 mg/kg F- for 24 h. The expression levels of myocardial Hsps were determined using RT-PCR, western blotting, and immunohistochemical studies. Acute F--intoxicated rats showed elevated levels of both the transcripts and protein expression of Hsf1, Hsp27, Hsp32, Hsp60, and Hsp70 when compared to control. In addition, the expression levels of Hsp40 and Hsp90 were significantly declined in a dose-dependent fashion in F--treated animals. Our result suggests that differential expression of Hsps in the rat myocardium could serve as a balance between pro-survival and death signal during acute F--induced heart failure.

Mitochondrial co-chaperone protein Tid1 is required for energy homeostasis during skeletal myogenesis

BACKGROUND

Tid1 is a mitochondrial co-chaperone protein and its transcript is abundantly expressed in skeletal muscle tissues. However, the physiological function of Tid1 during skeletal myogenesis remains unclear.

METHODS

In vitro induced differentiation assay of mouse myoblast C2C12 cells was applied to examine the physiological role of Tid1 during skeletal myogenesis. In addition, transgenic mice with muscle specific (HSA-Cre) Tid1 deletion were established and examined to determine the physiological function of Tid1 during skeletal muscle development in vivo.

RESULTS

Expression of Tid1 protein was upregulated in the differentiated C2C12 cells, and the HSA-Tid1^f/f mice displayed muscular dystrophic phenotype. The expression of myosin heavy chain (MyHC), the protein served as the muscular development marker, was reduced in HSA-Tid1^f/f mice at postnatal day (P)5 and P8. The protein levels of ATP sensor (p-AMPK) and mitochondrial biogenesis protein (PGC-1α) were also significantly reduced in HSA-Tid1^f/f mice. Moreover, Tid1 deficiency induced apoptotic marker Caspase-3 in muscle tissues of HSA-Tid1^f/f mice. Consistent with the in vivo finding, we observed that downregulation of Tid1 not only reduced the ATP production but also abolished the differentiation ability of C2C12 cells by impairing the mitochondrial activity.

CONCLUSION

Together, our results suggest that Tid1 deficiency reduces ATP production and abolishes mitochondrial activity, resulting in energy imbalance and promoting apoptosis of muscle cells during myogenesis. It will be of importance to understand the function of Tid1 during human muscular dystrophy in the future.

Identification of the molecular mechanisms underlying dilated cardiomyopathy via bioinformatic analysis of gene expression profiles

In the present study, gene expression profiles of patients with dilated cardiomyopathy (DCM) were re-analyzed with bioinformatics tools to investigate the molecular mechanisms underlying DCM. Gene expression dataset GSE3585 was downloaded from Gene Expression Omnibus, which included seven heart biopsy samples obtained from patients with DCM and five healthy controls. Differential analysis was performed using a Limma package in R to screen for differentially expressed genes (DEGs). Functional enrichment analysis was subsequently conducted for DEGs using the Database for Annotation, Visualization and Integration Discovery. A protein-protein interaction (PPI) network was constructed using information from Search Tool for the Retrieval of Interacting Genes software. A total of 89 DEGs were identified in the patients with DCM, including 67 upregulated and 22 downregulated genes. Functional enrichment analysis demonstrated that the downregulated genes predominantly encoded chromosomal proteins and transport-related proteins, which were significantly associated with the biological processes of ‘nucleosome assembly’, ‘chromatin assembly’, ‘protein-DNA complex assembly’, ‘nucleosome organization’ and ‘DNA packaging’ (H1 histone family member 0, histone cluster 1 H1c, histone cluster 1 H2bd and H2A histone family member Z). The upregulated genes detected in the present study encoded secreted proteins or phosphotransferase, which were associated with biological processes including ‘cell adhesion’ [connective tissue growth factor (CTGF)], ‘skeletal system development’ [CTGF and insulin-like growth factor binding protein 3 (IGFBP3)], ‘muscle organ development’ (SMAD7) and ‘regulation of cell migration’ [SMAD7, IGFBP3 and insulin receptor (INSR)]. Notably, signal transducer and activator of transcription 3, SMAD7, INSR, CTGF, exportin 1, IGFBP3 and phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha were hub nodes with the higher degree in the PPI network. Therefore, the results of the present study suggested that DEGs may alter the biological processes of ‘nucleosome formation’, ‘cell adhesion’, ‘skeletal system development’, ‘muscle organ development’ and ‘regulation of cell migration’ in the development of DCM.

Satellite RNAs promote pancreatic oncogenic processes via the dysfunction of YBX1

Highly repetitive tandem arrays at the centromeric and pericentromeric regions in chromosomes, previously considered silent, are actively transcribed, particularly in cancer. This aberrant expression occurs even in K-ras-mutated pancreatic intraepithelial neoplasia (PanIN) tissues, which are precancerous lesions. To examine the biological roles of the satellite RNAs in carcinogenesis, we construct mouse PanIN-derived cells expressing major satellite (MajSAT) RNA and show increased malignant properties. We find an increase in frequency of chromosomal instability and point mutations in both genomic and mitochondrial DNA. We identify Y-box binding protein 1 (YBX1) as a protein that binds to MajSAT RNA. MajSAT RNA inhibits the nuclear translocation of YBX1 under stress conditions, thus reducing its DNA-damage repair function. The forced expression of YBX1 significantly decreases the aberrant phenotypes. These findings indicate that during the early stage of cancer development, satellite transcripts may act as 'intrinsic mutagens' by inducing YBX1 dysfunction, which may be crucial in oncogenic processes.

Cardiomyocyte-Specific Human Bcl2-Associated Anthanogene 3 P209L Expression Induces Mitochondrial Fragmentation, Bcl2-Associated Anthanogene 3 Haploinsufficiency, and Activates p38 Signaling

The Bcl2-associated anthanogene (BAG) 3 protein is a member of the BAG family of cochaperones, which supports multiple critical cellular processes, including critical structural roles supporting desmin and interactions with heat shock proteins and ubiquitin ligases intimately involved in protein quality control. The missense mutation P209L in exon 3 results in a primarily cardiac phenotype leading to skeletal muscle and cardiac complications. At least 10 other Bag3 mutations have been reported, nine resulting in a dilated cardiomyopathy for which no specific therapy is available. We generated αMHC-human Bag3 P209L transgenic mice and characterized the progressive cardiac phenotype in vivo to investigate its utility in modeling human disease, understand the underlying molecular mechanisms, and identify potential therapeutic targets. We identified a progressive heart failure by echocardiography and Doppler analysis and the presence of pre-amyloid oligomers at 1 year. Paralleling the pathogenesis of neurodegenerative diseases (eg, Parkinson disease), pre-amyloid oligomers-associated alterations in cardiac mitochondrial dynamics, haploinsufficiency of wild-type BAG3, and activation of p38 signaling were identified. Unexpectedly, increased numbers of activated cardiac fibroblasts were identified in Bag3 P209L Tg+ hearts without increased fibrosis. Together, these findings point to a previously undescribed therapeutic target that may have application to mutation-induced myofibrillar myopathies as well as other common causes of heart failure that commonly harbor misfolded proteins.

BRG1 and BRM SWI/SNF ATPases redundantly maintain cardiomyocyte homeostasis by regulating cardiomyocyte mitophagy and mitochondrial dynamics in vivo

There has been an increasing recognition that mitochondrial perturbations play a central role in human heart failure. Mitochondrial networks, whose function is to maintain the regulation of mitochondrial biogenesis, autophagy ('mitophagy') and mitochondrial fusion/fission, are new potential therapeutic targets. Yet our understanding of the molecular underpinning of these processes is just emerging. We recently identified a role of the SWI/SNF ATP-dependent chromatin remodeling complexes in the metabolic homeostasis of the adult cardiomyocyte using cardiomyocyte-specific and inducible deletion of the SWI/SNF ATPases BRG1 and BRM in adult mice (Brg1/Brm double mutant mice). To build upon these observations in early altered metabolism, the present study looks at the subsequent alterations in mitochondrial quality control mechanisms in the impaired adult cardiomyocyte. We identified that Brg1/Brm double-mutant mice exhibited increased mitochondrial biogenesis, increases in 'mitophagy', and alterations in mitochondrial fission and fusion that led to small, fragmented mitochondria. Mechanistically, increases in the autophagy and mitophagy-regulated proteins Beclin1 and Bnip3 were identified, paralleling changes seen in human heart failure. Evidence for perturbed cardiac mitochondrial dynamics included decreased mitochondria size, reduced numbers of mitochondria, and an altered expression of genes regulating fusion (Mfn1, Opa1) and fission (Drp1). We also identified cardiac protein amyloid accumulation (aggregated fibrils) during disease progression along with an increase in pre-amyloid oligomers and an upregulated unfolded protein response including increased GRP78, CHOP, and IRE-1 signaling. Together, these findings described a role for BRG1 and BRM in mitochondrial quality control, by regulating mitochondrial number, mitophagy, and mitochondrial dynamics not previously recognized in the adult cardiomyocyte. As critical to the pathogenesis of heart failure, epigenetic mechanisms like SWI/SNF chromatin remodeling seem more intimately linked to cardiac function and mitochondrial quality control mechanisms than previously realized.

Mitochondrial Dynamics and Heart Failure

Mitochondrial dynamics, fission and fusion, were first identified in yeast with investigation in heart cells beginning only in the last 5 to 7 years. In the ensuing time, it has become evident that these processes are not only required for healthy mitochondria, but also, that derangement of these processes contributes to disease. The fission and fusion proteins have a number of functions beyond the mitochondrial dynamics. Many of these functions are related to their membrane activities, such as apoptosis. However, other functions involve other areas of the mitochondria, such as OPA1's role in maintaining cristae structure and preventing cytochrome c leak, and its essential (at least a 10 kDa fragment of OPA1) role in mtDNA replication. In heart disease, changes in expression of these important proteins can have detrimental effects on mitochondrial and cellular function.

Fenofibrate unexpectedly induces cardiac hypertrophy in mice lacking MuRF1

The muscle-specific ubiquitin ligase muscle ring finger-1 (MuRF1) is critical in regulating both pathological and physiological cardiac hypertrophy in vivo. Previous work from our group has identified MuRF1's ability to inhibit serum response factor and insulin-like growth factor-1 signaling pathways (via targeted inhibition of cJun as underlying mechanisms). More recently, we have identified that MuRF1 inhibits fatty acid metabolism by targeting peroxisome proliferator-activated receptor alpha (PPARα) for nuclear export via mono-ubiquitination. Since MuRF1-/- mice have an estimated fivefold increase in PPARα activity, we sought to determine how challenge with the PPARα agonist fenofibrate, a PPARα ligand, would affect the heart physiologically. In as little as 3 weeks, feeding with fenofibrate/chow (0.05% wt/wt) induced unexpected pathological cardiac hypertrophy not present in age-matched sibling wild-type (MuRF1+/+) mice, identified by echocardiography, cardiomyocyte cross-sectional area, and increased beta-myosin heavy chain, brain natriuretic peptide, and skeletal muscle α-actin mRNA. In addition to pathological hypertrophy, MuRF1-/- mice had an unexpected differential expression in genes associated with the pleiotropic effects of fenofibrate involved in the extracellular matrix, protease inhibition, hemostasis, and the sarcomere. At both 3 and 8 weeks of fenofibrate treatment, the differentially expressed MuRF1-/- genes most commonly had SREBP-1 and E2F1/E2F promoter regions by TRANSFAC analysis (54 and 50 genes, respectively, of the 111 of the genes >4 and <-4 log fold change; P ≤ .0004). These studies identify MuRF1's unexpected regulation of fenofibrate's pleiotropic effects and bridges, for the first time, MuRF1's regulation of PPARα, cardiac hypertrophy, and hemostasis.

COP9 signalosome controls the degradation of cytosolic misfolded proteins and protects against cardiac proteotoxicity

RATIONALE

Impaired degradation of misfolded proteins is associated with a large subset of heart diseases. Misfolded proteins are degraded primarily by the ubiquitin-proteasome system, but the ubiquitin ligases responsible for the degradation remain largely unidentified. The cullin deneddylation activity of the COP9 signalosome (CSN) requires all 8 CSN subunits (CSN1 through CSN8) and regulates cullin-RING ligases, thereby controlling ubiquitination of a large number of proteins; however, neither CSN nor cullin-RING ligases is known to regulate the degradation of cytosolic misfolded proteins.

OBJECTIVE

We sought to investigate the role of CSN8/CSN in misfolded protein degradation and cardiac proteinopathy.

METHODS AND RESULTS

Cardiac CSN8 knockout causes mouse premature death; hence, CSN8 hypomorphism (CSN8(hypo)) mice were used. Myocardial neddylated forms of cullins were markedly increased, and myocardial capacity of degrading a surrogate misfolded protein was significantly reduced by CSN8 hypomorphism. When introduced into proteinopathic mice in which a bona fide misfolded protein R120G missense mutation of αβ-crystallin (CryAB(R120G)) is overexpressed in the heart, CSN8 hypomorphism aggravated CryAB(R120G)-induced restrictive cardiomyopathy and shortened the lifespan of CryAB(R120G) mice, which was associated with augmented accumulation of protein aggregates, increased neddylated proteins, and reduced levels of total ubiquitinated proteins and LC3-II in the heart. In cultured cardiomyocytes, both CSN8 knockdown and cullin-RING ligase inactivation suppressed the ubiquitination and degradation of CryAB(R120G) but not native CryAB, resulting in accumulation of protein aggregates and exacerbation of CryAB(R120G) cytotoxicity.

CONCLUSIONS

(1) CSN8/CSN promotes the ubiquitination and degradation of misfolded proteins and protects against cardiac proteotoxicity, and (2) cullin-RING ligases participate in degradation of cytosolic misfolded proteins.

The role of HSP70 and its co-chaperones in protein misfolding, aggregation and disease

Molecular chaperones and their associated co-chaperones are essential in health and disease as they are key facilitators of protein folding, quality control and function. In particular, the HSP70 molecular chaperone networks have been associated with neurodegenerative diseases caused by aberrant protein folding. The pathogenesis of these disorders usually includes the formation of deposits of misfolded, aggregated protein. HSP70 and its co-chaperones have been recognised as potent modulators of inclusion formation and cell survival in cellular and animal models of neurodegenerative disease. In has become evident that the HSP70 chaperone machine functions not only in folding, but also in proteasome mediated degradation of neurodegenerative disease proteins. Thus, there has been a great deal of interest in the potential manipulation of molecular chaperones as a therapeutic approach for many neurodegenerations. Furthermore, mutations in several HSP70 co-chaperones and putative co-chaperones have been identified as causing inherited neurodegenerative and cardiac disorders, directly linking the HSP70 chaperone system to human disease.

Mitochondrial heat shock protein machinery hsp70/hsp40 is indispensable for proper mitochondrial DNA maintenance and replication

Mitochondrial chaperones have multiple functions that are essential for proper functioning of mitochondria. In the human-pathogenic protist Trypanosoma brucei, we demonstrate a novel function of the highly conserved machinery composed of mitochondrial heat shock proteins 70 and 40 (mtHsp70/mtHsp40) and the ATP exchange factor Mge1. The mitochondrial DNA of T. brucei, also known as kinetoplast DNA (kDNA), is represented by a single catenated network composed of thousands of minicircles and dozens of maxicircles packed into an electron-dense kDNA disk. The chaperones mtHsp70 and mtHsp40 and their cofactor Mge1 are uniformly distributed throughout the single mitochondrial network and are all essential for the parasite. Following RNA interference (RNAi)-mediated depletion of each of these proteins, the kDNA network shrinks and eventually disappears. Ultrastructural analysis of cells depleted for mtHsp70 or mtHsp40 revealed that the otherwise compact kDNA network becomes severely compromised, a consequence of decreased maxicircle and minicircle copy numbers. Moreover, we show that the replication of minicircles is impaired, although the lack of these proteins has a bigger impact on the less abundant maxicircles. We provide additional evidence that these chaperones are indispensable for the maintenance and replication of kDNA, in addition to their already known functions in Fe-S cluster synthesis and protein import.

Impairment or loss of mitochondrial DNA is associated with mitochondrial dysfunction and a wide range of neural, muscular, and other diseases. We present the first evidence showing that the entire mtHsp70/mtHsp40 machinery plays an important role in mitochondrial DNA replication and maintenance, a function likely retained from prokaryotes. These abundant, ubiquitous, and multifunctional chaperones share phenotypes with enzymes engaged in the initial stages of replication of the mitochondrial DNA in T. brucei.

Mitochondrial heat shock protein machinery hsp70/hsp40 is indispensable for proper mitochondrial DNA maintenance and replication

Mitochondrial chaperones have multiple functions that are essential for proper functioning of mitochondria. In the human-pathogenic protist Trypanosoma brucei, we demonstrate a novel function of the highly conserved machinery composed of mitochondrial heat shock proteins 70 and 40 (mtHsp70/mtHsp40) and the ATP exchange factor Mge1. The mitochondrial DNA of T. brucei, also known as kinetoplast DNA (kDNA), is represented by a single catenated network composed of thousands of minicircles and dozens of maxicircles packed into an electron-dense kDNA disk. The chaperones mtHsp70 and mtHsp40 and their cofactor Mge1 are uniformly distributed throughout the single mitochondrial network and are all essential for the parasite. Following RNA interference (RNAi)-mediated depletion of each of these proteins, the kDNA network shrinks and eventually disappears. Ultrastructural analysis of cells depleted for mtHsp70 or mtHsp40 revealed that the otherwise compact kDNA network becomes severely compromised, a consequence of decreased maxicircle and minicircle copy numbers. Moreover, we show that the replication of minicircles is impaired, although the lack of these proteins has a bigger impact on the less abundant maxicircles. We provide additional evidence that these chaperones are indispensable for the maintenance and replication of kDNA, in addition to their already known functions in Fe-S cluster synthesis and protein import.

IMPORTANCE

Impairment or loss of mitochondrial DNA is associated with mitochondrial dysfunction and a wide range of neural, muscular, and other diseases. We present the first evidence showing that the entire mtHsp70/mtHsp40 machinery plays an important role in mitochondrial DNA replication and maintenance, a function likely retained from prokaryotes. These abundant, ubiquitous, and multifunctional chaperones share phenotypes with enzymes engaged in the initial stages of replication of the mitochondrial DNA in T. brucei.

Development of pharmacological strategies for mitochondrial disorders

Mitochondrial diseases are an unusually genetically and phenotypically heterogeneous group of disorders, which are extremely challenging to treat. Currently, apart from supportive therapy, there are no effective treatments for the vast majority of mitochondrial diseases. Huge scientific effort, however, is being put into understanding the mechanisms underlying mitochondrial disease pathology and developing potential treatments. To date, a variety of treatments have been evaluated by randomized clinical trials, but unfortunately, none of these has delivered breakthrough results. Increased understanding of mitochondrial pathways and the development of many animal models, some of which are accurate phenocopies of human diseases, are facilitating the discovery and evaluation of novel prospective treatments. Targeting reactive oxygen species has been a treatment of interest for many years; however, only in recent years has it been possible to direct antioxidant delivery specifically into the mitochondria. Increasing mitochondrial biogenesis, whether by pharmacological approaches, dietary manipulation or exercise therapy, is also currently an active area of research. Modulating mitochondrial dynamics and mitophagy and the mitochondrial membrane lipid milieu have also emerged as possible treatment strategies. Recent technological advances in gene therapy, including allotopic and transkingdom gene expression and mitochondrially targeted transcription activator-like nucleases, have led to promising results in cell and animal models of mitochondrial diseases, but most of these techniques are still far from clinical application.

A splicing mutation in the novel mitochondrial protein DNAJC11 causes motor neuron pathology associated with cristae disorganization, and lymphoid abnormalities in mice

Mitochondrial structure and function is emerging as a major contributor to neuromuscular disease, highlighting the need for the complete elucidation of the underlying molecular and pathophysiological mechanisms. Following a forward genetics approach with N-ethyl-N-nitrosourea (ENU)-mediated random mutagenesis, we identified a novel mouse model of autosomal recessive neuromuscular disease caused by a splice-site hypomorphic mutation in a novel gene of unknown function, DnaJC11. Recent findings have demonstrated that DNAJC11 protein co-immunoprecipitates with proteins of the mitochondrial contact site (MICOS) complex involved in the formation of mitochondrial cristae and cristae junctions. Homozygous mutant mice developed locomotion defects, muscle weakness, spasticity, limb tremor, leucopenia, thymic and splenic hypoplasia, general wasting and early lethality. Neuropathological analysis showed severe vacuolation of the motor neurons in the spinal cord, originating from dilatations of the endoplasmic reticulum and notably from mitochondria that had lost their proper inner membrane organization. The causal role of the identified mutation in DnaJC11 was verified in rescue experiments by overexpressing the human ortholog. The full length 63 kDa isoform of human DNAJC11 was shown to localize in the periphery of the mitochondrial outer membrane whereas putative additional isoforms displayed differential submitochondrial localization. Moreover, we showed that DNAJC11 is assembled in a high molecular weight complex, similarly to mitofilin and that downregulation of mitofilin or SAM50 affected the levels of DNAJC11 in HeLa cells. Our findings provide the first mouse mutant for a putative MICOS protein and establish a link between DNAJC11 and neuromuscular diseases.

Mutant ubiquitin UBB+1 induces mitochondrial fusion by destabilizing mitochondrial fission-specific proteins and confers resistance to oxidative stress-induced cell death in astrocytic cells

Mutant ubiquitin UBB+1 is observed in a variety of aging-related neurodegenerative diseases and acts as a potent inhibitor of the ubiquitin proteasome system (UPS). In the present study, we investigated the relationship between impaired UPS (using ectopic expression of UBB+1) and mitochondrial dynamics in astrocytes, which are the most abundant glial cells in the central nervous system. Immunocytochemistry and fluorescence recovery after photobleaching revealed that ectopic expression of UBB+1 induced mitochondrial elongation. We further demonstrated that overexpression of UBB+1 destabilized mitochondrial fission-specific proteins including Drp1, Fis1, and OPA3, but not the mitochondrial fusion-specific proteins Mfn1, Mfn2, and OPA1. The reduction in mitochondrial fission-specific proteins by UBB+1 was prevented by inhibiting the 26 S proteasome using chemical inhibitors, including MG132, lactacystin and epoxomicin. We then assessed the involvement of proteases that target mitochondrial proteins by using various protease inhibitors. Finally, we confirmed that either overexpression of UBB+1 or inhibiting the proteasome can protect astrocytic cells from H₂O₂-induced cell death compared with control cells. Our results suggest that UBB+1 destabilizes mitochondrial fission-specific proteins, leading to mitochondrial fusion and the subsequent resistance to oxidative stress. We therefore propose a protective role of UBB+1 overexpression or the proteasome inhibition in astrocytes in degenerative brains.

Keep your heart in shape: molecular chaperone networks for treating heart disease

Despite major advances in the treatment of cardiac diseases, there is still a great need for drugs capable of counteracting the deterioration of cardiac muscle function in congestive heart failure. The role of misfolded protein accumulation as a causal event in the physiopathology of common cardiac diseases is an important emerging concept. Indeed, diverse stress conditions, including mechanical stretching and oxidative stress, can induce misfolded protein accumulation, causing cardiomyocyte death. Cells react to these stress conditions by activating molecular chaperones, a class of proteins that represents an endogenous salvage machinery, essential for rescuing physiological cell functions and sustaining cell survival. Chaperones, also known as heat shock proteins (Hsps), prevent accumulation of damaged proteins by promoting either their refolding or degradation via the proteasome or the autophagosome systems. In addition, molecular chaperones play a key role in intracellular signalling by controlling conformational changes required for activation/deactivation of signalling proteins, and their assembly in specific signalosome complexes. The key role of molecular chaperones in heart function is highlighted by the fact that a number of genetic mutations in chaperone proteins result in different forms of cardiomyopathies. Moreover, a considerable amount of experimental evidence indicates that increasing expression of chaperone proteins leads to an important cardio-protective role in ischaemia/reperfusion injury, heart failure, and arrhythmia, implicating these molecules as potential innovative therapeutic agents.

Essential role of TID1 in maintaining mitochondrial membrane potential homogeneity and mitochondrial DNA integrity

The tumorous imaginal disc 1 (TID1) protein localizes mainly to the mitochondrial compartment, wherein its function remains largely unknown. Here we report that TID1 regulates the steady-state homogeneity of the mitochondrial membrane potential (Δψ) and maintains the integrity of mitochondrial DNA (mtDNA). Silencing of TID1 with RNA interference leads to changes in the distribution of Δψ along the mitochondrial network, characterized by an increase in Δψ in focal regions. This effect can be rescued by ectopic expression of a TID1 construct with an intact J domain. Chronic treatment with a low dose of oligomycin, an inhibitor of F1Fo ATP synthase, decreases the cellular ATP content and phenocopies TID1 loss of function, indicating a connection between the disruption of mitochondrial bioenergetics and hyperpolarization. Prolonged silencing of TID1 or low-dose oligomycin treatment leads to the loss of mtDNA and the consequent inhibition of oxygen consumption. Biochemical and colocalization data indicate that complex I aggregation underlies the focal accumulation of Δψ in TID1-silenced cells. Given that TID1 is proposed to function as a cochaperone, these data show that TID1 prevents complex I aggregation and support the existence of a TID1-mediated stress response to ATP synthase inhibition.

DHTKD1 is essential for mitochondrial biogenesis and function maintenance

Maintaining the functional integrity of mitochondria is crucial for cell function, signal transduction and overall cell activities. Mitochondrial dysfunctions may alter energy metabolism and in many cases are associated with neurological diseases. Recent studies have reported that mutations in dehydrogenase E1 and transketolase domain-containing 1 (DHTKD1), a mitochondrial protein encoding gene, could cause neurological abnormalities. However, the function of DHTKD1 in mitochondria remains unknown. Here, we report a strong correlation of DHTKD1 expression level with ATP production, revealing the fact that DHTKD1 plays a critical role in energy production in mitochondria. Moreover, suppression of DHTKD1 leads to impaired mitochondrial biogenesis and increased reactive oxygen species (ROS), thus leading to retarded cell growth and increased cell apoptosis. These findings demonstrate that DHTKD1 contributes to mitochondrial biogenesis and function maintenance.

T-cell intracellular antigen (TIA)-proteins deficiency in murine embryonic fibroblasts alters cell cycle progression and induces autophagy

Mice lacking either T-cell intracellular antigen 1 (TIA1) or TIA1 related/like protein (TIAR/TIAL1) show high rates of embryonic lethality, suggesting a relevant role for these proteins during embryonic development. However, intrinsic molecular and cellular consequences of either TIA1 or TIAR deficiency remain poorly defined. By using genome-wide expression profiling approach, we demonstrate that either TIA1 or TIAR inactivation broadly alter normal development-associated signalling pathways in murine embryonic fibroblasts (MEF). Indeed, these analyses highlighted alterations of cytokine-cytokine and ECM-receptor interactions and Wnt, MAPK, TGF-beta dependent signalling pathways. Consistent with these results, TIA1 and TIAR knockout (KO) MEF show reduced rates of cell proliferation, cell cycle progression delay and increased cell size. Furthermore, TIA-proteins deficiency also caused metabolic deficiencies, increased ROS levels and DNA damage, promoting a gentle rise of cell death. Concomitantly, high rates of autophagy were detected in both TIA1 and TIAR KO MEF with induction of the formation of autophagosomes, as evidenced by the up-regulation of the LC3B protein, and autolysosomes, measured by colocalization of LC3B and LAMP1, as a survival mechanism attempt. Taken together, these observations support that TIA proteins orchestrate a transcriptome programme to activate specific developmental decisions. This program is likely to contribute to mouse physiology starting at early stages of the embryonic development. TIA1/TIAR might function as cell sensors to maintain homeostasis and promote adaptation/survival responses to developmental stress.

Insights from the clustering of microarray data associated with the heart disease

Heart failure (HF) is the major of cause of mortality and morbidity in the developed world. Gene expression profiles of animal model of heart failure have been used in number of studies to understand human cardiac disease. In this study, statistical methods of analysing microarray data on cardiac tissues from dogs with pacing induced HF were used to identify differentially expressed genes between normal and two abnormal tissues. The unsupervised techniques principal component analysis (PCA) and cluster analysis were explored to distinguish between three different groups of 12 arrays and to separate the genes which are up regulated in different conditions among 23912 genes in heart failure canines' microarray data. It was found that out of 23912 genes, 1802 genes were differentially expressed in the three groups at 5% level of significance and 496 genes were differentially expressed at 1% level of significance using one way analysis of variance (ANOVA). The genes clustered using PCA and clustering analysis were explored in the paper to understand HF and a small number of differentially expressed genes related to HF were identified.

Nucleoid localization of Hsp40 Mdj1 is important for its function in maintenance of mitochondrial DNA

Faithful replication and propagation of mitochondrial DNA (mtDNA) is critical for cellular respiration. Molecular chaperones, ubiquitous proteins involved in protein folding and remodeling of protein complexes, have been implicated in mtDNA transactions. In particular, cells lacking Mdj1, an Hsp40 co-chaperone of Hsp70 in the mitochondrial matrix, do not maintain functional mtDNA. Here we report that the great majority of Mdj1 is associated with nucleoids, DNA-protein complexes that are the functional unit of mtDNA transactions. Underscoring the importance of Hsp70 chaperone activity in the maintenance of mtDNA, an Mdj1 variant having an alteration in the Hsp70-interacting J-domain does not maintain mtDNA. However, a J-domain containing fragment expressed at the level that Mdj1 is normally present is not competent to maintain mtDNA, suggesting a function of Mdj1 beyond that carried out by its J-domain. Nevertheless, loss of mtDNA function upon Mdj1 depletion is retarded when the J-domain, is overexpressed. Analysis of Mdj1 variants revealed a correlation between nucleoid association and DNA maintenance activity, suggesting that localization is functionally important. We found that Mdj1 has DNA binding activity and that variants retaining DNA-binding activity also retained nucleoid association. Together, our results are consistent with a model in which Mdj1, tethered to the nucleoid via DNA binding, thus driving a high local concentration of the Hsp70 machinery, is important for faithful DNA maintenance and propagation.

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J-protein co-chaperone Mdj1 is critical for maintenance of functional mtDNA.

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Majority of Mdj1 localizes to the nucleoid, likely via interaction with mtDNA.

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Nucleoid localization of Mdj1 is necessary for mtDNA maintenance.

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Function of Mdj1 in mtDNA maintenance requires cooperation with Hsp70.

Targeted disruption of Hspa4 gene leads to cardiac hypertrophy and fibrosis

Failure of molecular chaperones to direct the correct folding of newly synthesized proteins leads to the accumulation of misfolded proteins in cells. HSPA4 is a member of the heat shock protein 110 family (HSP110) that acts as a nucleotide exchange factor of HSP70 chaperones. We found that the expression of HSPA4 is upregulated in murine hearts subjected to pressure overload and in failing human hearts. To investigate the cardiac function of HSPA4, Hspa4 knockout (KO) mice were generated and exhibited cardiac hypertrophy and fibrosis. Hspa4 KO hearts were characterized by a significant increase in heart weight/body weight ratio, elevated expression of hypertrophic and fibrotic gene markers, and concentric hypertrophy with preserved contractile function. In response to pressure overload, cardiac hypertrophy and remodeling were further aggravated in the Hspa4 KO compared to wild type (WT) mice. Cardiac hypertrophy in Hspa4 KO hearts was associated with enhanced activation of gp130-STAT3, CaMKII, and calcineurin-NFAT signaling. Protein blot and immunofluorescent analyses showed a significant accumulation of polyubiquitinated proteins in cardiac cells of Hspa4 KO mice. These results suggest that the myocardial remodeling of Hspa4 KO mice is due to accumulation of misfolded proteins resulting from impaired chaperone activity. Further analyses revealed a significant increase in cross sectional area of cardiomyocytes, and in expression levels of hypertrophic markers in cultured neonatal Hspa4 KO cardiomyocytes suggesting that the hypertrophy of mutant mice was a result of primary defects in cardiomyocytes. Gene expression profile in hearts of 3.5-week-old mice revealed a differentially expressed gene sets related to ion channels, muscle-specific contractile proteins and stress response. Taken together, our in vivo data demonstrate that Hspa4 gene ablation results in cardiac hypertrophy and fibrosis, possibly, through its role in protein quality control mechanism.

Mitochondrial chaperone DnaJA3 induces Drp1-dependent mitochondrial fragmentation

Mitochondrial morphology is dynamic and controlled by coordinated fusion and fission pathways. The role of mitochondrial chaperones in mitochondrial morphological changes and pathology is currently unclear. Here we report that altered levels of DnaJA3 (Tid1/mtHsp40) a mitochondrial member of the DnaJ protein family, and heat shock protein (Hsp) co-chaperone of matrix 70 kDa Hsp70 (mtHsp70/mortalin/HSPA9), induces mitochondrial fragmentation. Suppression of DnaJA3 induced mitochondrial fragmentation in HeLa cells. Elevated levels of DnaJA3 in normal Hs68 fibroblast cells and HeLa, SKN-SH, U87 and U251 cancer cell lines induces mitochondrial fragmentation. Mitochondrial fragmentation induction was not observed in HeLa cells when other DnaJA family members, or mitochondrial DnaJ protein HSC20, were ectopically expressed, indicating that the effects on mitochondrial morphology were specific to DnaJA3. We show that the DnaJ domain (amino acids 88-168) of DnaJA3 is sufficient for the induction of mitochondrial fragmentation. Furthermore, an H121Q point mutation of the DnaJ domain, which abrogates interaction and activation of mtHsp70 ATPase, eliminates fragmentation induced by DnaJA3. This suggests that DnaJA3 interaction with mtHsp70 may be critical in mitochondrial morphological changes. DnaJA3-induced mitochondrial fragmentation was dependent on fission factor dynamin-related protein 1 (Drp1). Ectopic expression of the mitofusins (Mfn1 and Mfn2), however, does not rescue DnaJA3-induced mitochondrial fragmentation. Lastly, elevated levels of DnaJA3 inducing mitochondrial fragmentation were associated with reduction in cell viability. Taken together, elevated DnaJA3 induces Drp1-depedendent mitochondrial fragmentation and decreased cell viability.

Proteotoxic stress and circulating cell stress proteins in the cardiovascular diseases

The cardiovasculature is one of the major body systems and probably the one most exposed to stress. There is clear evidence that increasing levels of cell stress proteins within the heart is cardioprotective. In addition, there is rapidly emerging evidence that secreted cell stress proteins play a role in the function of the cardiovascular tissues. Those secreted proteins have three potential functions: (1) as normal homeostatic cardiovascular signals (e.g. protein disulphide isomerase); (2) as anti-inflammatory molecules, which are able to inhibit cardiovascular pathology (e.g. Hsp27); and (iii) as pro-inflammatory signals that can induce and promote cardiovascular pathology (e.g. Hsp60). As all of these various proteins may be released-at different rates-and in different cardiovascular diseases-we need to consider the cohort of potential secreted cell stress proteins as a dynamic system (network) that can aid and/or damage the equally dynamic cardiovascular system.

Cellular stress stimulates nuclear localization signal (NLS) independent nuclear transport of MRJ

HSP40 family member MRJ (DNAJB6) has been in the spot light for its relevance to Huntington's, Parkinson's diseases, limb-girdle muscular dystrophy, placental development, neural stem cells, cell cycle and malignancies such as breast cancer and melanoma. This gene has two spliced variants coding for 2 distinct proteins with significant homology. However, MRJ(L) (large variant) is predominantly localized to the nucleus whereas MRJ(S) (small variant) is predominantly cytoplasmic. Interestingly MRJ(S) translocates to the nucleus in response to heat shock. The classical heat shock proteins respond to crises (stress) by increasing the number of molecules, usually by transcriptional up-regulation. Our studies imply that a quick increase in the molar concentration of MRJ in the nuclear compartment is a novel method by which MRJ responds to stress. We found that MRJ(S) shows NLS (nuclear localization signal) independent nuclear localization in response to heat shock and hypoxia. The specificity of this response is realized due to lack of such response by MRJ(S) when challenged by other stressors, such as some cytokines or UV light. Deletion analysis has allowed us to narrow down on a 20 amino acid stretch at the C-terminal region of MRJ(S) as a potential stress sensing region. Functional studies indicated that constitutive nuclear localization of MRJ(S) promoted attributes of malignancy such as proliferation and invasiveness overall indicating distinct phenotypic characteristics of nuclear MRJ(S).

Loss of proteostatic control as a substrate for atrial fibrillation: a novel target for upstream therapy by heat shock proteins

Atrial fibrillation (AF) is the most common, sustained clinical tachyarrhythmia associated with significant morbidity and mortality. AF is a persistent condition with progressive structural remodeling of the atrial cardiomyocytes due to the AF itself, resulting in cellular changes commonly observed in aging and in other heart diseases. While rhythm control by electrocardioversion or drug treatment is the treatment of choice in symptomatic AF patients, its efficacy is still limited. Current research is directed at preventing first-onset AF by limiting the development of substrates underlying AF progression and resembles mechanism-based therapy. Upstream therapy refers to the use of non-ion channel anti-arrhythmic drugs that modify the atrial substrate- or target-specific mechanisms of AF, with the ultimate aim to prevent the occurrence (primary prevention) or recurrence of the arrhythmia following (spontaneous) conversion (secondary prevention). Heat shock proteins (HSPs) are molecular chaperones and comprise a large family of proteins involved in the protection against various forms of cellular stress. Their classical function is the conservation of proteostasis via prevention of toxic protein aggregation by binding to (partially) unfolded proteins. Our recent data reveal that HSPs prevent electrical, contractile, and structural remodeling of cardiomyocytes, thus attenuating the AF substrate in cellular, Drosophila melanogaster, and animal experimental models. Furthermore, studies in humans suggest a protective role for HSPs against the progression from paroxysmal AF to persistent AF and in recurrence of AF. In this review, we discuss upregulation of the heat shock response system as a novel target for upstream therapy to prevent derailment of proteostasis and consequently progression and recurrence of AF.