Daily Endocrinology Research Analysis

Selective and controlled expansion of endogenous β cells has been pursued as a potential therapy for diabetes. Ideally, such therapies would preserve feedback control of β cell proliferation to avoid excessive β cell expansion. Here, we identified a regulator of β cell proliferation whose inactivation resulted in controlled β cell expansion: the protein deacetylase sirtuin 2 (SIRT2). Sirt2 deletion in β cells of mice increased β cell proliferation during hyperglycemia with little effect under homeostatic conditions, indicating preservation of feedback control of β cell mass. SIRT2 restrains proliferation of human islet β cells, demonstrating conserved SIRT2 function. Analysis of acetylated proteins in islets treated with a SIRT2 inhibitor revealed that SIRT2 deacetylates enzymes involved in oxidative phosphorylation, dampening the adaptive increase in oxygen consumption during hyperglycemia. At the transcriptomic level, Sirt2 inactivation has context-dependent effects on β cells, with Sirt2 controlling how β cells interpret hyperglycemia as a stress. Finally, we provide proof of principle that systemic administration of a glucagon-like peptide 1-coupled (GLP1-coupled), Sirt2-targeting antisense oligonucleotide achieves β cell Sirt2 inactivation and stimulates β cell proliferation during hyperglycemia. Overall, these studies identify a therapeutic strategy for increasing β cell mass in diabetes without circumventing feedback control of β cell proliferation. Future work should test the extent to which these findings translate to human β cells from individuals with or without diabetes.

Bioactive glycerolysophospholipids (GLPs) are implicated in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) and obesity; however, the mechanisms underlying glycerolysophospholipid-mediated changes in insulin signaling remain poorly understood. Here, we identify the amino acid-metabolism enzyme asparaginase (ASPG) as a critical regulator of systemic fatty acid handling and insulin signal transduction. Hepatic ASPG expression levels negatively correlate with insulin sensitivity in humans. Loss of Aspg in MASLD mice modifies the liver hepatokine secretome, enhancing systemic insulin sensitivity. Notably, ASPG bears lysophospholipase activity towards the bioactive lipid lysophosphatidylinositol (LPI) in vitro and in vivo. Mechanistically, Aspg deficiency results in accumulation of intracellular LPIs and consequently in suppression of tyrosine phosphatase PTP1B activity. This in turn decreases FOXO1-dependent expression of the hepatokine Sepp1, leading to reduced SEPP1 secretion and extrahepatic insulin-sensitization. In summary, this study uncovers a novel biological mechanism whereby ASPG-controlled bioactive lipid levels modulate insulin resistance and insulin secretion, suggesting complementary therapeutic strategies for the improvement of systemic glucose homeostasis.

Olfactomedin-2 (OLFM2) is a pleiotropic glycoprotein emerging as a regulator of energy homeostasis. We here show the expression of OLFM2 to be adipocyte-specific and inversely associated with obesity. OLFM2 levels increase during adipogenesis and are suppressed in inflamed adipocytes. Functionally, OLFM2 deficiency impairs adipocyte differentiation, while its over-production enhances the adipogenic transformation of fat cell progenitors. Loss and gain of function experiments revealed that OLFM2 modulates key metabolic and structural pathways, including PPAR signaling, citrate cycle, fatty acid degradation, axon guidance and focal adhesion in 3T3 cell lines and primary human adipocytes. On the molecular level, OLFM2 deficiency in differentiated adipocytes predominantly downregulates genes involved in cell cycle. Extending these findings in vivo, both whole-body Olfm2 knockout and adipose-specific Olfm2 depletion in mice resulted in impaired adipose cell cycle gene expression, with the latter also displaying fat mass accretion and metabolic dysfunction. Collectively, our results underscore a critical role for OLFM2 in adipocyte biology, and support a causative link between reduced adipose OLFM2 and the pathophysiology of obesity.