Role of the DNAJ/HSP40 family in the pathogenesis of insulin resistance and type 2 diabetes

Heat Shock Proteins (HSPs) and Cardiovascular Complications of Obesity: Searching for Potential Biomarkers

Heat shock proteins (HSPs), a family of proteins that support cellular proteostasis and perform a protective function under various stress conditions, such as high temperature, intoxication, inflammation, or tissue hypoxia, constitute a promising group of possible biochemical markers for obesity and cardiovascular diseases. HSP27 is involved in essential cellular processes occurring in conditions of obesity and its cardiometabolic complications; it has protective properties, and its secretion may indicate a cellular response to stress. HSP40 plays a controversial role in the pathogenesis of obesity. HSP60 is involved in various pathological processes of the cardiovascular, immune, excretory, and nervous systems and is associated with obesity and concomitant diseases. The hypersecretion of HSP60 is associated with poor prognosis; hence, this protein may become a target for further research on obesity and its cardiovascular complications. According to most studies, intracellular HSP70 is an obesity-promoting factor, whereas extracellular HSP70 exhibited inconsistent dynamics across different patient groups and diagnoses. HSPs are involved in the pathogenesis of cardiovascular pathology. However, in the context of cardiovascular and metabolic pathology, these proteins require further investigation.

The role of heat shock proteins (HSPs) in type 2 diabetes mellitus pathophysiology

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by sustained hyperglycemia caused by impaired insulin signaling and secretion. Metabolic stress, caused by an inappropriate diet, is one of the major hallmarks provoking inflammation, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction. Heat shock proteins (HSPs) are a group of highly conserved proteins that have a crucial role in chaperoning damaged and misfolded proteins to avoid disruption of cellular homeostasis under stress conditions. To do this, HSPs interact with diverse intra-and extracellular pathways among which are the insulin signaling, insulin secretion, and apoptosis pathways. Therefore, HSP dysfunction, e.g. HSP70, may lead to disruption of the pathways responsible for insulin secretion and uptake. Consistently, the altered expression of other HSPs and genetic polymorphisms in HSP-producing genes in diabetic subjects has made HSPs hot research in T2DM. This paper provides a comprehensive overview of the role of different HSPs in T2DM pathogenesis, affected cellular pathways, and the potential therapeutic strategies targeting HSPs in T2DM.

Genetic Deletion of DNAJB3 Using CRISPR-Cas9, Produced Discordant Phenotypes

Several pathways and/or genes have been shown to be dysregulated in obesity-induced insulin resistance (IR) and type 2 diabetes (T2D). We previously showed, for the first time, impaired expression of DNAJB3 mRNA and protein in subjects with obesity, which was concomitant with increased metabolic stress. Restoring the normal expression of DNAJB3 attenuated metabolic stress and improved insulin signaling both in vivo and in vitro, suggesting a protective role of DNAJB3 against obesity and T2D. The precise underlying mechanisms remained, however, unclear. This study was designed to confirm the human studies in a mouse model of dietary obesity-induced insulin resistance, and, if validated, to understand the underlying mechanisms. We hypothesized that mice lacking DNAJB3 would be more prone to high-fat (HF)-diet-induced increase in body weight and body fat, inflammation, glucose intolerance and insulin resistance as compared with wild-type (WT) littermates. Three DNAJB3 knockout (KO) lines were generated (KO 30, 44 and 47), using CRISPR-Cas9. Male and female KO and WT mice were fed a HF diet (45% kcal fat) for 16 weeks. Body weight was measured biweekly, and a glucose tolerance test (GTT) and insulin tolerance test (ITT) were conducted at week 13 and 14, respectively. Body composition was determined monthly by nuclear magnetic resonance (NMR). Following euthanasia, white adipose tissue (WAT) and skeletal muscle were harvested for further analyses. Compared with WT mice, male and female KO 47 mice demonstrated higher body weight and fat mass. Similarly, KO 47 mice also showed a slower rate of glucose clearance in GTT that was consistent with decreased mRNA expression of the GLUT4 gene in WAT but not in the muscle. Both male and female KO 47 mice exhibited higher mRNA levels of the pro-inflammatory marker TNF-a in WAT only, whereas increased mRNA levels of MCP1 chemokine and the ER stress marker BiP/Grp78 were observed in male but not in female KO 47 mice. However, we did not observe the same changes in the other KO lines. Taken together, the phenotype of the DNAJB3 KO 47 mice was consistent with the metabolic changes and low levels of DNAJB3 reported in human subjects. These findings suggest that DNAJB3 may play an important role in metabolic functions and glucose homeostasis, which warrants further phenotyping and intervention studies in other KO 47 and other KO mice, as well as investigating this protein as a potential therapeutic target for obesity and T2D.

DNAJB7 is dispensable for male fertility in mice

BACKGROUND

DNAJBs are highly conserved proteins that are involved in various biological processes. Although several DNAJBs are highly expressed in the testis, the function of DNAJB7 in spermatogenesis and male fertility remains unclear.

METHODS

To identify the role of DNAJB7 in the male reproduction process, Dnajb7-deficient mice were generated by the CRISPR/Cas9-mediated genome editing system. Histological and immunofluorescence assays were performed to analyze the phenotype of the Dnajb7 mutants.

RESULTS

DNAJB7 is specifically expressed in haploid germ cells. Dnajb7 knockout mice are fertile and do not have any detectable defects in Sertoli cells, spermatogonia, meiotic and postmeiotic cells, indicating that DNAJB7 is not essential for spermatogenesis.

CONCLUSIONS

Our findings suggest that DNAJB7 is dispensable for male fertility in mice, which could prevent duplicative work by other groups.

Histone acetyltransferase HAM1 interacts with molecular chaperone DNAJA2 and confers immune responses through salicylic acid biosynthetic genes in cassava

Cassava bacterial blight (CBB) is one of the most serious diseases in cassava production, so it is essential to explore the underlying mechanism of immune responses. Histone acetylation is an important epigenetic modification, however, its relationship with cassava disease resistance remains unclear. Here, we identified 10 histone acetyltransferases in cassava and found that the transcript of MeHAM1 showed the highest induction to CBB. Functional analysis showed that MeHAM1 positively regulated disease resistance to CBB through modulation of salicylic acid (SA) accumulation. Further investigation revealed that MeHAM1 directly activated SA biosynthetic genes' expression via promoting lysine 9 of histone 3 (H3K9) acetylation and lysine 5 of histone 4 (H4K5) acetylation of these genes. In addition, molecular chaperone MeDNAJA2 physically interacted with MeHAM1, and MeDNAJA2 also regulated plant immune responses and SA biosynthetic genes. In conclusion, this study illustrates that MeHAM1 and MeDNAJA2 confer immune responses through transcriptional programming of SA biosynthetic genes via histone acetylation. The MeHAM1 & MeDNAJA2-SA biosynthesis module not only constructs the direct relationship between histone acetylation and cassava disease resistance, but also provides gene network with potential value for genetic improvement of cassava disease resistance.

The roles of HSP40/DNAJ protein family in neurodegenerative diseases

Molecular chaperones and co-chaperones facilitate the assembly of newly synthesized polypeptides and refolding of unfolded or misfolded proteins, thereby maintaining protein homeostasis in cells. As co-chaperones of the master chaperone heat shock protein (HSP) 70, the HSP40 (DNAJ) proteins are largest chaperone family in eukaryotic cells. They contain a characteristic J-domain which mediates interaction with HSP70, thereby helping protein folding. It is well perceived that protein homeostasis is vital for neuronal health. DNAJ family proteins have been linked to the occurrence and progression of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, spinocerebellar ataxia, Charcot-Marie-Tooth disease, spinal muscular atrophy, distal hereditary motor neuropathy, limb-girdle type muscular dystrophy, neuronal ceroid lipofuscinosis and essential tremor in recent studies. DNAJA1 effectively degrades huntington aggregates; DNAJB1 can degrade protein aggregates ataxin-3; DNAJB2 can inhibit the formation of huntington aggregates; DNAJB6 can inhibit the aggregation of Aβ ₄₂ and α-synuclein; DNAJC5 can promote the release of TDP-43, τ protein, and α-synuclein into the extracellular space. Mutations in the essential tremor-associated DNAJC13 gene can prevent endosome protein trafficking. This article reviews the mechanism of DNAJ protein family in neurodegenerative diseases.

Genetic Analysis of HSP40/DNAJ Family Genes in Parkinson's Disease: a Large Case-Control Study

Molecular chaperones were reported to play an important role in PD pathogenesis. Recent studies revealed the association of several HSP40/DNAJ family genes with PD, but no genetic analysis of all the DNAJ family genes in PD has been conducted. To systematically analyze the genetic impact of all the DNAJ family genes in PD, we performed genetic analysis for these genes in a large case-control study. We analyzed the rare variants in 49 DNAJ family genes from 3879 PD patients and 2931 healthy controls by whole-exome sequencing and whole-genome sequencing. All rare missense variants and the subgroups of rare damaging missense (Dmis) and loss-of-function (LoF) variants were gathered to test the accumulated association of these variants in each gene with PD. In total, 1617 rare nonsynonymous variants of DNAJ family genes with minor allele frequency less than 1% were identified in our cohort. We identified 82 rare missense variants for DNAJC26 in sporadic early-onset PD (sEOPD) or familial PD (FPD), and 17 Dmis and one LoF variant were detected among them. Gene-based burden analysis showed that the rare Dmis variants alone or Dmis plus LoF variants together of DNAJC26 were significantly enriched in PD patients. We also found suggestive associations of DNAJB2 and DNAJC18 with PD in sEOPD or FPD and DNAJC2, DNAJC10, DNAJC22, DNAJC24, DNAJC27, DNAJC28, and DNAJC29 with PD in sporadic late-onset PD. In conclusion, rare missense variants of DNAJC26 were significantly enriched in FPD or sEOPD. Moreover, DNAJB2, DNAJC2, DNAJC10, DNAJC18, DNAJC22, DNAJC24, DNAJC27, DNAJC28, and DNAJC29 were suggestively associated with PD.

Loss of ERdj5 exacerbates oxidative stress in mice with alcoholic liver disease via suppressing Nrf2

Alcoholic liver disease is the major cause of chronic liver diseases. Excessive alcohol intake results in endoplasmic reticulum (ER) stress. ERdj5, a member of DNAJ family, is an ER-resident chaperone protein, whose role in alcoholic liver disease remains to be investigated. In this study, we aim to address the effect of ERdj5 on alcoholic liver disease and the underlying mechanism. Hepatic Dnajc10 (ERdj5) mRNA expression was elevated in both human and mouse alcoholic hepatitis. In mice subjected to chronic and binge ethanol feeding, ERdj5 levels were also markedly increased. Hepatic Dnajc10 correlated with Xbp1s mRNA. Tunicamycin, an ER stress inducer, increased ERdj5 levels. Dnajc10 knockout mice exhibited exacerbated alcohol-induced liver injury and hepatic steatosis. However, the macrophage numbers and chemokine levels were similar to those in wild-type mice. Depletion of Dnajc10 promoted oxidative stress. Ethanol feeding increased hepatic H₂O₂ levels, and these were further increased in Dnajc10 knockout mice. Additionally, Dnajc10-deficient hepatocytes produced large amounts of reactive oxygen species. Notably, Nrf2, a central regulator of oxidative stress, was decreased by depletion of Dnajc10 in the nuclear fraction of ethanol-treated mouse liver. Consistently, liver tissues from ethanol-fed Dnajc10 knockout mice had reduced expression of downstream antioxidant genes. Furthermore, hepatic glutathione content in the liver of knockout mice declined compared to wild-type mice. In conclusion, our results demonstrate that ethanol-induced ERdj5 may regulate the Nrf2 pathway and glutathione contents, and have protective effects on liver damage and alcohol-mediated oxidative stress in mice. These suggest that ERdj5 has the potential to protect against alcoholic liver disease.

The mouse nicotinamide mononucleotide adenylyltransferase (NMNAT) chaperones diverse pathological amyloid client proteins

Molecular chaperones safeguard cellular protein homeostasis and obviate proteotoxicity. In the process of aging, as chaperone networks decline, aberrant protein amyloid aggregation accumulates in a mechanism that underpins neurodegeneration, leading to pathologies such as Alzheimer’s disease and Parkinson’s disease. Thus, it is important to identify and characterize chaperones for preventing such protein aggregation. In this work, we identified that the NAD⁺ synthase–nicotinamide mononucleotide adenylyltransferase (NMNAT) 3 from mouse (mN3) exhibits potent chaperone activity to antagonize aggregation of a wide spectrum of pathological amyloid client proteins including α-synuclein, Tau (K19), amyloid β, and islet amyloid polypeptide. By combining NMR spectroscopy, cross-linking mass spectrometry, and computational modeling, we further reveal that mN3 uses different region of its amphiphilic surface near the active site to directly bind different amyloid client proteins. Our work demonstrates a client recognition mechanism of NMNAT via which it chaperones different amyloid client proteins against pathological aggregation and implies a potential protective role for NMNAT in different amyloid-associated diseases.

Air pollution and metabolic syndrome risk: Evidence from nine observational studies

BACKGROUND AND AIMS

Globally, the number of metabolic syndrome (MetS) cases has increased substantially over time. However, the association between air pollution (AP) and MetS risk has been contradictory in observational studies. This is the first reported meta-analysis quantitatively exploring the aforementioned association.

METHODS

We searched PubMed, Embase, and Web of Science database entries up to September 14, 2020, and searches were updated up to December 6, 2020 to identify eligible articles on the AP-MetS risk association. No language restriction was imposed. Random-effects models were applied to estimate summary and subgroup effect sizes with 95% confidence intervals (CIs). PROSPERO registration number: CRD42020210431.

RESULTS

Eight articles (nine studies) were eligible for the meta-analysis. Increased MetS prevalence was not found to be associated with particulate matter less than 1 μm (PM₁), 2.5 μm (PM_2.5), and 10 μm (PM₁₀) in diameter or nitrogen dioxide (NO₂), and the summary effect sizes were 1.33 (95% CI: 0.95-1.85), 1.34 (95% CI: 0.96-1.89), 1.18 (95% CI: 0.98-1.19), and 1.28 (95% CI: 0.89-1.82), respectively, based on cross-sectional studies. The summary results indicated no association between each 10 μg/m³ increase in PM_2.5 and MetS incidence (effect size 2.78 [95% CI: 0.70-11.02]), based on cohort studies. Subgroup analysis demonstrated that MetS incidence in older men increased dramatically by 992% with each 10 μg/m³ increase in PM_2.5.

CONCLUSIONS

The evidence presented here suggests that although exposure to PM₁, PM_2.5, PM₁₀, or NO₂ was not found to have a significant association with the occurrence of MetS, the statistical significance of the relationship between exposure to PM₁, PM_2.5, or PM₁₀ and MetS prevalence was approximately borderline. More studies on AP-MetS risk association in low-/middle-income countries, as well as on the association between other air pollutants and MetS risk, are warranted. A sufficient number of high-quality studies is required to perform a meaningful meta-analysis of the relationship between air pollutants and MetS.

T Cell Protein Tyrosine Phosphatase in Glucose Metabolism

T cell protein tyrosine phosphatase (TCPTP), a vital regulator in glucose metabolism, inflammatory responses, and tumor processes, is increasingly considered a promising target for disease treatments and illness control. This review discusses the structure, substrates and main biological functions of TCPTP, as well as its regulatory effect in glucose metabolism, as an attempt to be referenced for formulating treatment strategies of metabolic disorders. Given the complicated regulation functions in different tissues and organs of TCPTP, the development of drugs inhibiting TCPTP with a higher specificity and a better biocompatibility is recognized as a promising therapeutic strategy for diabetes or obesity. Besides, treatments targeting TCPTP in a specific tissue or organ are suggested to be considerably promising.

Plasma heat shock protein response to euglycemia in type 2 diabetes

INTRODUCTION

Glucose variability is associated with mortality and macrovascular diabetes complications. The mechanisms through which glucose variability mediates tissue damage are not well understood, although cellular oxidative stress is likely involved. As heat shock proteins (HSPs) play a role in the pathogenesis of type 2 diabetes (T2D) complications and are rapidly responsive, we hypothesized that HSP-related proteins (HSPRPs) would differ in diabetes and may respond to glucose normalization.

RESEARCH DESIGN AND METHODS

A prospective, parallel study in T2D (n=23) and controls (n=23) was undertaken. T2D subjects underwent insulin-induced blood glucose normalization from baseline 7.6±0.4 mmol/L (136.8±7.2 mg/dL) to 4.5±0.07 mmol/L (81±1.2 mg/dL) for 1 hour. Control subjects were maintained at 4.9±0.1 mmol/L (88.2±1.8 mg/dL). Slow Off-rate Modified Aptamer-scan plasma protein measurement determined a panel of HSPRPs.

RESULTS

At baseline, E3-ubiquitin-protein ligase (carboxyl-terminus of Hsc70 interacting protein (CHIP) or HSPABP2) was lower (p=0.03) and ubiquitin-conjugating enzyme E2G2 higher (p=0.003) in T2D versus controls. Following glucose normalization, DnaJ homolog subfamily B member 1 (DNAJB1 or HSP40) was reduced (p=0.02) in T2D, with HSP beta-1 (HSPB1) and HSP-70-1A (HSP70-1A) (p=0.07 and p=0.09, respectively) also approaching significance relative to T2D baseline levels.

CONCLUSIONS

Key HSPRPs involved in critical protein interactions, CHIP and UBE2G2, were altered in diabetes at baseline. DNAJB1 fell in response to euglycemia, suggesting that HSPs are reacting to basal stress that could be mitigated by tight glucose control with reduction of glucose variability.