Hepatic DNAJB9 Drives Anabolic Biasing to Reduce Steatosis and Obesity

High-fat-diet-induced hepatic insulin resistance per se attenuates murine de novo lipogenesis

Hepatic insulin resistance (IR) is often said to be "pathway-selective" with preserved insulin stimulation of de novo lipogenesis (DNL) despite attenuated insulin signaling toward glucose metabolism. However, DNL has not been assessed in models of liver-specific IR. We studied mice with differential tissue-specific lipid-induced IR achieved by different durations of high-fat diet (HFD) feeding. Mice with isolated hepatic IR demonstrated markedly reduced DNL, with a rebound seen in mice with whole-body IR. Insr T1150A mice (protected against diacylglycerol-PKCε-induced hepatic IR) maintained normal DNL with HFD feeding. During hyperinsulinemic clamps, hepatic IR reduced DNL, but hyperglycemia augmented DNL in both resistant and sensitive animals. Regulation through SREBP1c did not consistently correlate with changes in DNL. These results demonstrate that hepatic IR is not pathway-selective, highlighting the primacy of lipogenic substrate in stimulation of DNL. Future therapeutics to reduce lipogenesis should target substrate drivers of DNL rather than targeting plasma insulin levels.

Diagnostic model based on key autophagy-related genes in intervertebral disc degeneration

BACKGROUND

Current research on autophagy is mainly focused on intervertebral disc tissues and cells, while there is few on human peripheral blood sample. therefore, this study constructed a diagnostic model to identify autophagy-related markers of intervertebral disc degeneration (IVDD).

METHODS

GSE150408 and GSE124272 datasets were acquired from the Gene Expression Omnibus database, and differential expression analysis was performed. The IVDD-autophagy genes were obtained using Weighted Gene Coexpression Network Analysis, and a diagnostic model was constructed and validated, followed by Gene Set Variation Analysis (GSVA) and Gene Set Enrichment Analysis (GSEA). Meanwhile, miRNA-gene and transcription factor-gene interaction networks were constructed. In addition, drug-gene interactions and target genes of methylprednisolone and glucosamine were analyzed.

RESULTS

A total of 1,776 differentially expressed genes were identified between IVDD and control samples, and the composition of the four immune cell types was significantly different between the IVDD and control samples. The Meturquoise and Mebrown modules were significantly related to immune cells, with significant differences between the control and IVDD samples. A diagnostic model was constructed using five key IVDD-autophagy genes. The area under the curve values of the model in the training and validation datasets were 0.907 and 0.984, respectively. The enrichment scores of the two pathways were significantly different between the IVDD and healthy groups. Eight pathways in the IVDD and healthy groups had significant differences. A total of 16 miRNAs and 3 transcription factors were predicted to be of great value. In total, 84 significantly related drugs were screened for five key IVDD-autophagy genes in the diagnostic model, and three common autophagy-related target genes of methylprednisolone and glucosamine were predicted.

CONCLUSION

This study constructs a reliable autophagy-related diagnostic model that is strongly related to the immune microenvironment of IVD. Autophagy-related genes, including PHF23, RAB24, STAT3, TOMM5, and DNAJB9, may participate in IVDD pathogenesis. In addition, methylprednisolone and glucosamine may exert therapeutic effects on IVDD by targeting CTSD, VEGFA, and BAX genes through apoptosis, as well as the sphingolipid and AGE-RAGE signaling pathways in diabetic complications.

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.

Gene regulation of RMR-related DNAJC6 on adipogenesis and mitochondria function in 3T3-L1 preadipocytes

In the pilot GWAS of children obesity, DNAJC6 gene was found as a regulator for resting metabolic rate (RMR) and obesity in children aged 8-9 years. To investigate whether DNAJC6 gene regulated obesity and energy metabolism, the physiological mechanisms during adipogenesis of 3T3-L1 preadipocytes were confirmed after DNAJC6 gene was overexpressed or inhibited. Overexpressing DNAJC6 gene maintained a 3T3-L1 preadipocyte status during cell differentiation (MTT, ORO, DAPI/BODIPY). It suppressed adipogenesis and adipokine production (leptin, adiponectin), insulin signaling with IRS-GLUT4 system (RT-PCR, Western blotting), and mitochondrial function (Mito Stress Test). DNAJC6 overexpressed cells inhibited mTOR expression, but maintained LC3 expression at a high level, indicating that autophagy occurred and energy was obtained. However, when DNAJC6 gene was inhibited, fat synthesis factor was highly expressed during differentiation (PPARr, C/EBPa, aP2, etc) and the intracellular stress level increased accordingly, which affected the reduction of reserve respiratory capacity during mitochondrial respiration. Our study confirmed gene regulation of DNAJC6, overexpression or inhibition, affects adipogenesis with energy metabolism and mitochondrial functions. This basic data can be used for clinic obesity studies to control an energy imbalance.

Polyethylene microplastics impede the innate immune response by disrupting the extracellular matrix and signaling transduction

Microplastics (MPs) can accumulate in animal organs. Numerous studies have linked MPs with immune system. However, the impact of MPs on immune response remains unclear. This study examined the innate immune response of mice exposed to 5 μm MPs. In the lipopolysaccharide challenge, mice treated with MPs exhibited lower levels of serum immune factors and activated immune cells. MPs disrupted immune-related receptors and cause dysfunction in cell signal transduction within the liver and spleen. Proteomic analysis revealed that MPs impede the activation of serum immune-related signals. In addition, the tissue section imaging exhibited a significant enrichment of MPs in the extracellular matrix (ECM), consistent with the ECM dysfunction and immune receptor suppression. Therefore, our data suggest excessive MPs accumulation in ECM inhibits cell signaling pathways, thereby suppressing the activation of immune responses. We propose the biotoxicity of MPs is partly through the MP disruption of ECM (MPDEM).

Regulation of calcium homeostasis and flux between the endoplasmic reticulum and the cytosol

The concentration of Ca²⁺ in the endoplasmic reticulum (ER) is critically important for maintaining its oxidizing environment as well as for maintaining luminal ATP levels required for chaperone activity. Therefore, local luminal Ca²⁺ concentrations and the dynamic Ca²⁺ flux between the different subcellular compartments are tightly controlled. Influx of Ca²⁺ into the ER is enabled by a reductive shift, which opens the sarcoendoplasmic reticulum calcium transport ATPase pump, building the Ca²⁺ gradient across the ER membrane required for ATP import. Meanwhile, Ca²⁺ leakage from the ER has been reported to occur via the Sec61 translocon following protein translocation. In this review, we provide an overview of the complex regulation of Ca²⁺ homeostasis, Ca²⁺ flux between subcellular compartments, and the cellular stress response (the unfolded protein response) induced upon dysregulated luminal Ca²⁺ metabolism. We also provide insight into the structure and gating mechanism at the Sec61 translocon and examine the role of ER-resident cochaperones in assisting the central ER-resident chaperone BiP in the control of luminal Ca²⁺ concentrations.

The function of the co-chaperone ERdj4 in diverse (patho-)physiological conditions

Accumulation of misfolded proteins in the endoplasmic reticulum (ER) induces a well-orchestrated cellular response to reduce the protein burden within the ER. This unfolded protein response (UPR) is controlled primarily by three transmembrane proteins, IRE1α, ATF6, and PERK, the activity of which is controlled by BiP, the ER-resident Hsp70 protein. Binding of BiP to co-chaperones via their highly conserved J-domains stimulates the intrinsic ATPase activity of BiP, thereby providing the energy necessary for (re-)folding of proteins, or for targeting of misfolded proteins to the degradation pathway, processes specified and controlled by the respective co-chaperone. In this review, our aim is to elucidate the function of the co-chaperone ERDJ4, also known as MDG1, MDJ7, or DNAJB9. Knockout and knockin experiments clearly point to the central role of ERDJ4 in controlling lipogenesis and protein synthesis by promoting degradation of SREBP1c and the assembly of the protein complex mTORC2. Accumulating data reveal that ERDJ4 controls epithelial-to-mesenchymal transition, a central process during embryogenesis, in wound healing, and tumor development. Overexpression of ERdj4 has been shown to improve engraftment of transplanted human stem cells, possibly due to its ability to promote cellular survival in stressed cells. High ERDJ4-plasma levels are specific for fibrillary glomerulonephritis and serve as a diagnostic marker. As outlined in this review, the functions of ERDJ4 are manifold, depending on the cellular (patho-) physiological state, the cellular protein repertoire, and the subcellular localization of ERDJ4.

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.

LncRNA-URHC Functions as ceRNA to Regulate DNAJB9 Expression by Competitively Binding to miR-5007-3p in Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is often diagnosed at a late stage, when the prognosis is poor. The regulation of long noncoding RNAs (lncRNAs) plays a crucial role in HCC. However, the precise regulatory mechanisms of lncRNA signaling in HCC remain largely unknown. Our study aims to investigate the underlying mechanisms of lncRNA (upregulated in hepatocellular carcinoma) URHC in HCC.

OBJECTIVE

To study the in vivo and in vitro localization and biological effects of URHC on liver cancer cells. Through bioinformatics analysis, dual-luciferase reporter gene analysis and rescue experiments revealed the possible mechanism of URHC.

METHODS

RT-qPCR, fluorescence in situ hybridization (FISH) staining, EdU, colony formation, and tumor xenograft experiments were used to identify localized and biological effects of URHC on HCC cells in vitro and in vivo. The bioinformatics analysis, dual-luciferase reporter assay, and rescue experiments revealed the potential mechanism of URHC.

RESULTS

URHC silencing may inhibit the HCC cells' proliferation in vitro and in vivo. We found that URHC was mainly localized in the cytoplasm. The expression of miR-5007-3p was negatively regulated by URHC. And miR-5007-3p could reverse the effect of URHC in HCC cells. The expression of DNAJB9 was negatively regulated by miR-5007-3p but positively regulated by URHC. These suggestive of lncRNA-URHC positively regulated the level of DNAJB9 by sponging miR-5007-3p.

CONCLUSION

Together, our study elucidated the role of URHC as a miRNA sponge in HCC and shed new light on lncRNA-directed diagnostics and therapeutics in HCC.

Dual topology of co-chaperones at the membrane of the endoplasmic reticulum

Dual topologies of proteins at the ER membrane are known for a variety of proteins allowing the same protein to exert different functions according to the topology adopted. A dual topology of the co-chaperone ERdj4, which resides in the endoplasmic reticulum (ER), was proposed recently, a thesis that we found to align all published data and existing controversies into one whole picture. The aim of this review is to reassess all primary data available in the literature on ER-resident Hsp40 co-chaperones with respect to their topology. After careful and critical analyses of all experimental data published so far, we identified, next to ERdj4, two other co-chaperones, ERdj3 and ERdj6, that also display features of a dual topology at the ER membrane. We assume that during cellular stress subpools of some ER-resident J protein can alter their topology so that these proteins can exert different functions in order to adapt to cellular stress.

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

Insulin resistance (IR) underpins a wide range of metabolic disorders including type 2 diabetes (T2D), metabolic syndrome and cardiovascular diseases. IR is characterized by a marked reduction in the magnitude and/or delayed onset of insulin to stimulate glucose disposal. This condition is due to defects in one or several intracellular intermediates of the insulin signaling cascade, ranging from insulin receptor substrate (IRS) inactivation to reduced glucose phosphorylation and oxidation. Genetic predisposition, as well as other precipitating factors such as aging, obesity, and sedentary lifestyles are among the risk factors underlying the pathogenesis of IR and its subsequent progression to T2D. One of the cardinal hallmarks of T2D is the impairment of the heat shock response (HSR). Human and animal studies provided compelling evidence of reduced expression of several components of the HSR (i.e. Heat shock proteins or HSPs) in diabetic samples in a manner that correlates with the degree of IR. Interventions that induce the HSR, irrespective of the means to achieve it, proved their effectiveness in enhancing insulin sensitivity and improving glycemic index. However, most of these studies have been focused on HSP70 family. In this review, we will focus on the novel role of DNAJ/HSP40 cochaperone family in metabolic diseases associated with IR.

A guide to understanding endoplasmic reticulum stress in metabolic disorders

BACKGROUND

The global rise of metabolic disorders, such as obesity, type 2 diabetes, and cardiovascular disease, demands a thorough molecular understanding of the cellular mechanisms that govern health or disease. The endoplasmic reticulum (ER) is a key organelle for cellular function and metabolic adaptation and, therefore disturbed ER function, known as "ER stress," is a key feature of metabolic disorders.

SCOPE OF REVIEW

As ER stress remains a poorly defined phenomenon, this review provides a general guide to understanding the nature, etiology, and consequences of ER stress in metabolic disorders. We define ER stress by its type of stressor, which is driven by proteotoxicity, lipotoxicity, and/or glucotoxicity. We discuss the implications of ER stress in metabolic disorders by reviewing evidence implicating ER phenotypes and organelle communication, protein quality control, calcium homeostasis, lipid and carbohydrate metabolism, and inflammation as key mechanisms in the development of ER stress and metabolic dysfunction.

MAJOR CONCLUSIONS

In mammalian biology, ER is a phenotypically and functionally diverse platform for nutrient sensing, which is critical for cell type-specific metabolic control by hepatocytes, adipocytes, muscle cells, and neurons. In these cells, ER stress is a distinct, transient state of functional imbalance, which is usually resolved by the activation of adaptive programs such as the unfolded protein response (UPR), ER-associated protein degradation (ERAD), or autophagy. However, challenges to proteostasis also impact lipid and glucose metabolism and vice versa. In the ER, sensing and adaptive measures are integrated and failure of the ER to adapt leads to aberrant metabolism, organelle dysfunction, insulin resistance, and inflammation. In conclusion, the ER is intricately linked to a wide spectrum of cellular functions and is a critical component in maintaining and restoring metabolic health.