Daily Endocrinology Research Analysis

Aberrant RNA splicing is tightly linked to diseases, including metabolic dysfunction-associated steatotic liver disease (MASLD). In this study, we revealed that minor intron splicing, a unique and conserved RNA processing event, is largely disrupted upon the progression of metabolic dysfunction-associated steatohepatitis (MASH) in mice and humans. We demonstrated that deficiency of minor intron splicing in the liver induced MASH transition upon obesity-induced insulin resistance and LXR activation. Mechanistically, inactivation of minor intron splicing led to minor intron retention of Insig1 and Insig2, resulting in premature termination of translation, which drove proteolytic activation of SREBP1c. This mechanism was conserved in patients with MASH. Notably, disrupted minor intron splicing activated glutamine reductive metabolism for de novo lipogenesis through induction of Idh1, which caused accumulation of ammonia in the liver, thereby initiating hepatic fibrosis upon LXR activation. Ammonia clearance or IDH1 inhibition blocked hepatic fibrogenesis and mitigated MASH progression. More importantly, overexpression of Zrsr1 restored minor intron retention and ameliorated the development of MASH, indicating that dysfunctional minor intron splicing is an emerging pathogenic mechanism that drives MASH progression. Additionally, our results suggest that reductive carboxylation flux triggered by minor intron retention in hepatocytes serves as a crucial checkpoint and potential target for MASH therapy.

Hereditary SDHB-mutant pheochromocytomas (PC) and paragangliomas (PG) are rare tumours with a high propensity to metastasize although their clinical behaviour is unpredictable. To characterize the genomic landscape of these tumours and identify metastasis biomarkers, we perform multi-omic analysis on 94 tumours from 79 patients using seven molecular methods. Sympathetic (chromaffin cell) and parasympathetic (non-chromaffin cell) PCPG have distinct molecular profiles reflecting their cell-of-origin and biochemical profile. TERT and ATRX-alterations are associated with metastatic PCPG and these tumours have an increased mutation load, and distinct transcriptional and telomeric features. Most PCPG have quiet genomes with some rare co-operative driver events, including EPAS1/HIF-2α mutations. Two mechanisms of acquired resistance to DNA alkylating chemotherapies are identifiable; MGMT overexpression and mismatch repair-deficiency causing hypermutation. Our comprehensive multi-omic analysis of SDHB-mutant PCPG therefore identifies features of metastatic disease and treatment response, expanding our understanding of these rare neuroendocrine tumours.

The interplay between intracellular and intravascular lipolysis is crucial for maintaining circulating lipid levels and systemic energy homeostasis. Adipose triglyceride lipase (ATGL) and lipoprotein lipase (LPL), the primary triglyceride (TG) lipases responsible for these two spatially separate processes, are highly expressed in adipose tissue. Yet the mechanisms underlying their coordinated regulation remain undetermined. Here, we demonstrate that genetic ablation of G0S2, a specific inhibitory protein of ATGL, completely abolished diet-induced hypertriglyceridemia and significantly attenuated atherogenesis in mice. These effects were attributable to enhanced whole-body TG clearance, not altered hepatic TG secretion. Specifically, G0S2 deletion increased circulating LPL concentration and activity, predominantly through LPL production from white adipose tissue (WAT). Strikingly, transplantation of G0S2-deficient WAT normalized plasma TG levels in mice with hypertriglyceridemia. In conjunction with improved insulin sensitivity and decreased ANGPTL4 expression, the absence of G0S2 enhanced the stability of LPL protein in adipocytes, a phenomenon that could be reversed upon ATGL inhibition. Collectively, these findings highlight the pivotal role of adipocyte G0S2 in regulating both intracellular and intravascular lipolysis, and the possibility of targeting G0S2 as a viable pharmacological approach to reducing levels of circulating TGs.