GADD45β stabilized by direct interaction with HSP72 ameliorates insulin resistance and lipid accumulation

Short-Term Fasting Induces Hepatocytes' Stress Response and Increases Their Resilience

Fasting leads to a range of metabolic adaptations that have developed through evolution, as humans and other mammals have unequal access to food over the circadian cycle and are therefore adapted to fasting and feeding cycles. We have investigated the role of a single fasting episode in rats in triggering the stress response of liver hepatocytes. Since the stress responses were observed in both animals and isolated cells, we investigated whether the effects of the animal stressor could persist in the cells after isolation. By measuring staurosporine-induced apoptosis, stress signalling, and oxidative and antioxidant responses in hepatocytes from fasted and ad libitum-fed animals, we found that only fasting animals elicited a stress response that prevented caspase-9 activation and persisted in isolated cells. The addition of glucose oxidase, a hydrogen peroxide-producing enzyme, to the cells from ad libitum-fed animals also led to a stress response phenotype and prevented the activation of caspase-9. A single fasting episode thus leads to a stress response in normal hepatocytes, with hydrogen peroxide as a second messenger that reduces the initiation of apoptosis. This finding is the first characterisation of a mechanism underlying the effects of fasting and provides a basis for the development of methods to increase the resilience of cells. These findings need to be taken into account when interpreting the results obtained in animal and cell research models to account for the effects of overnight fasting used in many laboratory protocols. The research results also form the basis for the development of clinical applications to increase the resistance of transplants and to improve the fitness of hepatocytes under acute stress conditions in liver and some metabolic diseases.

Contradictory Role of Gadd45β in Liver Diseases

There are three homologous proteins (α, β and γ) in the growth arrest and DNA damage 45 (Gadd45) family. These proteins act as cellular responders to physiological and environmental stimuli. Gadd45β plays a significant role in the pathogenesis of liver diseases. Liver injury and growth stimulation increase expression of Gadd45β, which promotes cell survival, growth and proliferation in normal liver cells. By contrast, Gadd45β plays a role in promoting apoptosis and inhibiting tumour function in hepatocellular carcinoma (HCC). Currently, it is believed that Gadd45β benefits the liver through two different pathways: binding to MAPK kinase 6 (MKK6) to increase PCD induced by p38 (inhibiting tumours) or binding to constitutive androstane receptor (CAR) to jointly activate transcription of liver synthesis metabolism (promoting liver regeneration). This article aims to systematically review the role of Gadd45β in liver diseases, including its regulatory mechanism on expression and involvement in liver cell damage, inflammation, fibrosis and HCC. In conclusion, we explore the potential of targeting Gadd45β as a therapeutic strategy for liver diseases.

Heat shock proteins (HSPs) in non-alcoholic fatty liver disease (NAFLD): from molecular mechanisms to therapeutic avenues

Non-alcoholic fatty liver disease (NAFLD), a spectrum of liver conditions characterized by fat accumulation without excessive alcohol consumption, represents a significant global health burden. The intricate molecular landscape underlying NAFLD pathogenesis involves lipid handling, inflammation, oxidative stress, and mitochondrial dysfunction, with endoplasmic reticulum (ER) stress emerging as a key contributor. ER stress triggers the unfolded protein response (UPR), impacting hepatic steatosis in NAFLD and contributing to inflammation, fibrosis, and progression to NASH and eventually hepatocellular carcinoma (HCC). Heat shock proteins (HSPs), including small HSPs such as HSP20 and HSP27, HSP60, HSP70, GRP78, and HSP90, are integral to cellular stress responses. They aid in protein folding, prevent aggregation, and facilitate degradation, thus mitigating cellular damage under stress conditions. In NAFLD, aberrant HSP expression and function contribute to disease pathogenesis. Understanding the specific roles of HSP subtypes in NAFLD offers insights into potential therapeutic interventions. This review discusses the involvement of HSPs in NAFLD pathophysiology and highlights their therapeutic potential. By elucidating the molecular mechanisms underlying HSP-mediated protection in NAFLD, this article aims to pave the way for the development of targeted therapies for this prevalent liver disorder.

Elucidation of the molecular mechanism of type 2 diabetes mellitus affecting the progression of nonalcoholic steatohepatitis using bioinformatics and network pharmacology: A review

Increasing evidence suggests that patients with diabetes are at increased risk of developing nonalcoholic steatohepatitis (NASH), but the underlying mechanisms that affect the progression of NASH remain unclear. In this study, we used bioinformatics and network pharmacology methods to explore the differentially expressed genes of NASH and the related genes of type 2 diabetes mellitus, and a total of 46 common targets were obtained. Gene ontology showed that the common targets were mainly involved in biological processes such as glucocorticoid, hormone, and bacterium responses. The Kyoto Encyclopedia of Genes and Genomes enrichment analysis signal pathways were mainly in colorectal cancer, amphetamine addition, the peroxisome proliferator-activated receptor signaling pathway, and the toll-like receptor signaling pathway. The protein-protein interaction network identified 8 hub genes, and the co-expression network was analyzed to obtain 7 related functions and mutual proportions of hub genes. A total of 120 transcription factors were predicted for hub genes. Hub genes were closely related to immune cells, including neutropils and eosinophils. In addition, we identified 15 potential candidate drugs based on hub genes that are promising for the treatment of NASH. Type 2 diabetes mellitus can affect the progression of NASH by changing hormone levels and inflammatory responses through multiple targets and signaling pathways. Eight hub genes are expected to be potential targets for subsequent treatment.

GADD45A: With or without you

The growth arrest and DNA damage inducible (GADD)45 family includes three small and ubiquitously distributed proteins (GADD45A, GADD45B, and GADD45G) that regulate numerous cellular processes associated with stress signaling and injury response. Here, we provide a comprehensive review of the current literature investigating GADD45A, the first discovered member of the family. We first depict how its levels are regulated by a myriad of genotoxic and non-genotoxic stressors, and through the combined action of intricate transcriptional, posttranscriptional, and even, posttranslational mechanisms. GADD45A is a recognized tumor suppressor and, for this reason, we next summarize its role in cancer, as well as the different mechanisms by which it regulates cell cycle, DNA repair, and apoptosis. Beyond these most well-known actions, GADD45A may also influence catabolic and anabolic pathways in the liver, adipose tissue and skeletal muscle, among others. Not surprisingly, GADD45A may trigger AMP-activated protein kinase activity, a master regulator of metabolism, and is known to act as a transcriptional coregulator of numerous nuclear receptors. GADD45A has also been reported to display a cytoprotective role by regulating inflammation, fibrosis and oxidative stress in several organs and tissues, and is regarded an important contributor for the development of heart failure. Overall data point to that GADD45A may play an important role in metabolic, neurodegenerative and cardiovascular diseases, and also autoimmune-related disorders. Thus, the potential mechanisms by which dysregulation of GADD45A activity may contribute to the progression of these diseases are also reviewed below.

Lian-Mei-Yin formula alleviates diet-induced hepatic steatosis by suppressing Yap1/FOXM1 pathway-dependent lipid synthesis

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, with a global prevalence of 25%. Patients with NAFLD are more likely to suffer from advanced liver disease, cardiovascular disease, or type II diabetes. However, unfortunately, there is still a shortage of FDA-approved therapeutic agents for NAFLD. Lian-Mei-Yin (LMY) is a traditional Chinese medicine formula used for decades to treat liver disorders. It has recently been applied to type II diabetes which is closely related to insulin resistance. Given that NAFLD is another disease involved in insulin resistance, we hypothesize that LMY might be a promising formula for NAFLD therapy. Herein, we verify that the LMY formula effectively reduces hepatic steatosis in diet-induced zebrafish and NAFLD model mice in a time- and dose-dependent manner. Mechanistically, LMY suppresses Yap1-mediated Foxm1 activation, which is crucial for the occurrence and development of NAFLD. Consequently, lipogenesis is ameliorated by LMY administration. In summary, the LMY formula alleviates diet-induced NAFLD in zebrafish and mice by inhibiting Yap1/Foxm1 signaling-mediated NAFLD pathology.

Downregulation of Gadd45β alleviates osteoarthritis by repressing lipopolysaccharide-induced fibroblast-like synoviocyte inflammation, proliferation and migration

OBJECTIVE

Gadd45β have a regulatory role in cellular inflammation, proliferation and migration. However, the role of Gadd45β in synovial inflammation in osteoarthritis (OA) remains to be explored. This study aimed to ascertain whether Gadd45β is involved in OA synovial inflammation.

METHODS

The rat model was induced by sodium iodoacetate and the cellular model was constructed with lipopolysaccharide (LPS)-induced fibroblast-like synoviocytes (FLSs). siRNA was applied to interfere with the expression of intracellular Gadd45β. Real-time quantitative polymerase chain reaction (RT-qPCR) and western blotting were used to detect the expression of Gadd45β mRNA and protein. The inflammation, proliferation, and migration of OA-FLSs were detected by enzyme-linked immunosorbent assay, cell scratch assay, 5-ethynyl-2'-deoxyuridine assay, etc. The effect of downregulation of Gadd45β on the nuclear factor-κB (NF-κB) pathway was investigated.

RESULTS

Expression of Gadd45β in OA rat synovial tissues and OA-FLSs was increased, and LPS treatment promoted cell proliferation and enhanced cell migration. Gadd45β interference inhibited the inflammation, proliferation and migration of cells induced by LPS. LPS promoted P65 expression in the nucleus and activated the NF-κB signaling pathway, whereas si-Gadd45β reversed this situation.

CONCLUSIONS

si-Gadd45β inhibited the inflammatory response, proliferation and migration of FLSs, and activation of the NF-κB signaling pathway, which could delay the progression of OA. Hence, it may become a potential therapeutic target for OA.

Identification of potential feature genes in non-alcoholic fatty liver disease using bioinformatics analysis and machine learning strategies

The prevalence of non-alcoholic fatty liver disease (NAFLD) and NAFLD-associated hepatocellular carcinoma (HCC) has continuously increased in recent years. Machine learning is an effective method for screening the feature genes of a disease for prediction, prevention and personalized treatment. Here, we used the "limma" package and weighted gene co-expression network analysis (WGCNA) to screen 219 NAFLD-related genes and found that they were mainly enriched in inflammation-related pathways. Four feature genes (AXUD1, FOSB, GADD45B, and SOCS2) were screened by LASSO regression and support vector machine-recursive feature elimination (SVM-RFE) machine learning algorithms. Therefore, a clinical diagnostic model with an area under the curve (AUC) value of 0.994 was constructed, which was superior to other indicators of NAFLD. Significant correlations existed between feature genes expression and steatohepatitis histology or clinical variables. These findings were also validated in external datasets and a mouse model. Finally, we found that feature genes expression was significantly decreased in NAFLD-associated HCC and that SOCS2 may be a prognostic biomarker. Our findings may provide new insights into the diagnosis, prevention and treatment targets of NAFLD and NAFLD-associated HCC.

Identification of MAP3K4 as a novel regulation factor of hepatic lipid metabolism in non-alcoholic fatty liver disease

Background

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder with abnormal lipid metabolism. The present study was to identify regulatory genes related to lipid droplets (LDs) abnormal accumulation in NAFLD.

Methods

transcriptomic analysis and bioinformatics analysis (GEO database) were used to identify potential genes in abnormal lipid metabolism of NAFLD. A candidate gene MAP3K4 expression were detected by immunohistochemistry staining in NAFLD and controls. RNA interference and immunoblotting were used to verify the roles of MAP3K4 in the formation of hepatic LDs.

Results

A total of 134 candidate genes were screened, including 44 up-regulated genes and 90 down-regulated genes. 29 genes in the protein–protein interaction (PPI) were selected as hub genes, including MAP3K4. The expression levels of MAP3K4 were positively correlated with NAFLD activity score (r = 0.702, p = 0.002). Furthermore, we found a positive correlation of MAP3K4 expression with serum total cholesterol (r = 0.564, p = 0.023), uric acid levels (r = 0.520, p = 0.039), and body mass index (r = 0.574, p = 0.020). Downregulation of MAP3K4 decreased LDs accumulation in HepG2 cells and reduced the expression of CGI-58 and Plin-2 by imbibition of JNK and group IVA cytosolic phospholipase A2 (cPLA2) activation.

Conclusion

The study revealed a number of regulatory genes related to hepatic lipid metabolism of NAFLD, and demonstrated that MAP3K4 played a pivotal role in the hepatic lipogenesis of NAFLD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03734-8.