Hepatocyte Deubiquitinating Enzyme OTUD5 Deficiency is a Key Aggravator for Metabolic Dysfunction-Associated Steatohepatitis by Disturbing Mitochondrial Homeostasis

DNA-RNA hybrids in inflammation: sources, immune response, and therapeutic implications

Cytoplasmic DNA-RNA hybrids are emerging as important immunogenic nucleic acids, that were previously underappreciated. DNA-RNA hybrids, formed during cellular processes like transcription and replication, or by exogenous pathogens, are recognized by pattern recognition receptors (PRRs), including cGAS, DDX41, and TLR9, which trigger immune responses. Post-translational modifications (PTMs) including ubiquitination, phosphorylation, acetylation, and palmitoylation regulate the activity of PRRs and downstream signaling molecules, fine-tuning the immune response. Targeting enzymes involved in DNA-RNA hybrid metabolism and PTMs regulation offers therapeutic potential for inflammatory diseases. Herein, we discuss the sources, immune response, and therapeutic implications of DNA-RNA hybrids in inflammation, highlighting the significance of DNA-RNA hybrids as potential targets for the treatment of inflammation.

USP25 directly interacts with and deubiquitinates PPARα to increase PPARα stability in hepatocytes and attenuate high-fat diet-induced MASLD in mice

Recent studies have implicated altered ubiquitination/de-ubiquitination pathway in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD). Here, we investigated the potential role of a deubiquitinase, ubiquitin-specific peptidase 25 (USP25), in MASLD. Analysis of mRNA profiling data showed that both human and mouse MASLD are associated with reduced expression of USP25 in hepatocytes. Usp25 deficiency exacerbated HFD-induced liver lipid accumulation and MASLD in mice. Rescue experiments with USP25 induction in hepatocytes protected mice against HFD-induced MASLD. Through comprehensive transcriptome sequence and pulldown-LC-MS/MS analysis, we identified that peroxisome proliferator-activated receptor α (PPARα) is involved in USP25's protective actions and may be the substrate protein of USP25. Cell-based experiments show that USP25 interacts with PPARα directly via its USP domain and the histidine at position 608 of USP25 exerts deubiquitination to increase protein stability by removing the K48 ubiquitin chain at PPARα's lysine at position 429. USP25 reduces palmitate (PA)-induced lipid accumulation in hepatocytes via increasing PPARα. Finally, we show that the protective effects of Usp25 induction are nullified in Ppara-deficient mice with HFD. In summary, this study presents a new USP25-PPARα axis in hepatocytes and highlights a novel function of USP25 in MASLD, suggesting that it may be targeted to combat the disease.

Metallothionein 1B attenuates inflammation and hepatic steatosis in MASH by inhibiting the AKT/PI3K pathway

Metabolic dysfunction-associated steatohepatitis (MASH) is a severe form of metabolic dysfunction-associated fatty liver disease metabolic dysfunction-associated steatohepatitis , characterized by hepatic steatosis, inflammation, and fibrosis. This study investigates the role and potential mechanisms of metallothionein 1B (MT1B) in MASH through bioinformatics analysis and experimental validation. quantitative reverse transcription PCR and Western blot analyses confirm that MT1B expression is significantly downregulated in liver tissues of MASH patients, in high-fat diet-induced mouse models, and in hepatocytes induced by FFAs. Further functional experiments show that upregulation of MT1B reduces intracellular triglycerides and total cholesterol levels, lipid droplet formation, and proinflammatory factors. In vivo experiments demonstrate that specific downregulation of hepatic MT1B expression via AAV8-shMT1B injection significantly increases triglyceride and total cholesterol levels, exacerbates lipid accumulation, and markedly elevates liver fibrosis and inflammatory factor expression. RNA-seq and bioinformatics analyses show that the AKT/PI3K pathway is significantly suppressed in MT1B-overexpressing cells. Further experiments indicate that AKT inhibition can reverse the lipid metabolism disorders and inflammatory responses caused by MT1B downregulation. Additionally, Zinc can promote the nuclear translocation of MTF1, leading to its binding to the MT1B promoter, thereby upregulating MT1B expression and ultimately mitigating MASH progression. These findings suggest that zinc-regulated MT1B plays a critical role in lipid metabolism and inflammatory responses by regulating the AKT/PI3K signaling pathway, influencing MASH progression.

OTUD5 promotes the inflammatory immune response by enhancing MyD88 oligomerization and Myddosome formation

Myddosome is an oligomeric complex required for the transmission of inflammatory signals from TLR/IL1Rs and consists of MyD88 and IRAK family kinases. However, the molecular basis for the self-assemble of Myddosome proteins and regulation of intracellular signaling remains poorly understood. Here, we identify OTUD5 acts as an essential regulator for MyD88 oligomerization and Myddosome formation. OTUD5 directly interacts with MyD88 and cleaves its K11-linked polyubiquitin chains at Lys95, Lys231 and Lys250. This polyubiquitin cleavage enhances MyD88 oligomerization after LPS stimulation, which subsequently promotes the recruitment of downstream IRAK4 and IRAK2 to form Myddosome and the activation of NF-κB and MAPK signaling and production of inflammatory cytokines. Consistently, Otud5-deficient mice are less susceptible to LPS- and CLP-induced sepsis. Taken together, our findings reveal a positive regulatory role of OTUD5 in MyD88 oligomerization and Myddosome formation, which provides new sights into the treatment of inflammatory diseases.