Biology subjects

Prieur, X.

Publications and source records attributed to Prieur, X..

4 recordsLinked to original sources

bioRxiv2025

Tripartite ER-Mitochondria-Lipid Droplets contact sites control adipocyte metabolic flexibility

Obesity is a major risk factor for cardiometabolic diseases, with adipocyte dysfunction playing a central role. Understanding how lipid storage and mobilization are regulated--and disrupted--in adipocytes is key to addressing obesity-associated complications. The ER-anchored protein Seipin controls lipid droplet (LD) biogenesis and maintenance, and its loss disrupts ER-LD contact sites. In humans, Seipin deficiency causes generalized lipodystrophy, a severe form of adipocyte dysfunction. We previously showed that Seipin also localizes at ER-mitochondria contact sites (MAM), where it regulates calcium exchange and mitochondrial function. Here, we examined whether Seipin targeting to MAM and ER-LD sites overlaps functionally. We analyzed subcutaneous adipose tissue (AT) from inducible Seipin-knockout mice using transmission electron microscopy (TEM) and proximity ligation assays (PLA) to quantify membrane contact sites (MCS) involving the ER, LDs, and mitochondria. In control mice, feeding reduced MAMs while increasing ER-LD and mitochondria-LD contacts, whereas Seipin deficiency abolished this remodeling. Specifically, under lipid loading, MAMs located in proximity to LDs--tripartite contact sites known as MAM-LD--were increased in control but not in Seipin-deficient adipocytes. Fluorescence recovery after photobleaching assays revealed that Seipin depletion impairs triglyceride transfer to LDs, an effect rescued by the MAM-LD-reinforcing synthetic peptide Linker-ER-Mi. Importantly, this rescue was abolished by silencing the mitochondrial calcium uniporter, demonstrating that calcium exchange is critical for triglyceride storage in LDs. We further investigated how MAM-LD remodeling influences adipocyte metabolic flexibility. Using TEM and PLA, we monitored two MAM subtypes: those forming MAM-LD and those engaging cytosolic mitochondria (MAM-CM). During adipogenesis, MAM-LD frequency increased while MAM-CM decreased. Similarly, in mouse AT and 3T3-L1 adipocytes, lipid loading selectively promoted MAM-LD. Notably, this adaptive remodeling of membrane contact sites was blunted in the adipose tissue of diet-induced obese mice. Genetic disruption of MCS in 3T3-L1 adipocytes altered lipid flux, impaired lipolysis, and reduced insulin signaling. Together, our findings identify MAM-LD contacts as key regulators of adipocyte lipid handling and metabolic flexibility, whose disruption may underlie the metabolic inflexibility of obesity.

cell biology↗

bioRxiv2025

Extracellular vesicles carrying surface-anchored adiponectin prevent obesity-related metabolic complications by enhancing insulin sensitivity

Adiponectin (Adpn) is a potent insulin-sensitizing adipokine with therapeutic promise for type 2 diabetes (T2D) and metabolic dysfunction-associated steatohepatitis (MASH). Its clinical use is limited by challenges in producing stable, bioactive high-molecular weight forms. Adipocyte-derived extracellular vesicles (EVs) naturally carry oligomeric Adpn on their surface, enhancing hormone stability and activity. Here, we engineered EVs displaying membrane-anchored Adpn (EVPP-Adpn) and control EVs lacking Adpn (EVCTL), and evaluated their metabolic effects in high fat diet (HFD)-induced obesity mice. EVPP-Adpn were purified from HEK293T cells stably transfected with a chimeric Adpn fused to a transmembrane domain and a pilot peptide (PP) directing it to EVs; EVCTL were produced from non-transfected cells. HFD-fed male and female mice received intraperitoneal EV injections for six weeks. EVPP-Adpn improved glucose tolerance and insulin sensitivity, promoted adipocyte lipid storage through insulin-regulated lipogenesis and alleviated MASH features (liver steatosis, inflammation and fibrosis). EVPP-Adpn lowered circulating ceramides and reduced FGF21, indicating improved hepatic metabolism, and activated AKT and AMPK pathways in liver and skeletal muscle, consistent with increased adiponectin signaling. These results demonstrate that surface-anchored Adpn EVs restore tissue-specific insulin signaling and improve obesity-related metabolic dysfunctions, highlighting their potential as a novel biotherapeutic strategy for T2D and MASH.

bioengineering↗

bioRxiv2024

Seipin Regulates Caveolin-1 Trafficking and Organelle Crosstalk

Caveolin-1 (CAV1), the main structural component of caveolae, is essential in various biological processes, including mechanotransduction, lipid metabolism, and endocytosis1-4. Deregulation of CAV1 dynamics is linked to various pathologies, including cellular senescence, cancer, insulin resistance, and lipodystrophy5-9. However, mechanisms regulating CAV1 trafficking and function remain poorly understood. Here, we show that seipin, a crucial lipid droplet (LD) biogenesis factor10, modulates CAV1 trafficking. Deletion of seipin resulted in the accumulation of saturated lipids, leading to ceramide and sphingomyelin overproduction, which disrupted the membrane order of the trans-Golgi network (TGN). In seipin deficiency, CAV1 location to the plasma membrane (PM) was impaired, reducing caveolae. Instead, CAV1 accumulated in TGN and late endosome compartments, which fused with LDs and delivered the protein. In wild-type (WT) cells, this process was minimal but significantly enhanced by treatment with palmitate, ceramide, or Stearoyl-CoA desaturase-1 (SCD1) inhibition. Conversely, in seipin-deficient cells, inhibiting Fatty Acid Synthase (FASN) or overexpressing SCD1 restored CAV1 localization to the PM and reduced its accumulation in LDs. Our findings reveal that seipin controls the funneling of palmitate toward glycerolipids synthesis and storage in LDs versus conversion to ceramides in the ER. This balance is crucial to cellular protein trafficking by controlling the TGN membrane order. Therefore, our study identifies seipin as a critical regulator of cellular lipid metabolism, protein trafficking, and organelle homeostasis. These findings shed light on the processes regulating CAV1 trafficking and show that convergent pathophysiological mechanisms associated with defects in CAV1 and seipin contribute to metabolic disorders, including insulin resistance and lipodystrophies11-14.

cell biology↗

bioRxiv2023

Insulin resistance-driven beta-cell adaptation in mice: Mechanistic characterization and 3D analysis

Aims/hypothesisPancreatic beta cells secrete insulin to control glucose homeostasis. Beta cells can also adapt their function and mass when more insulin is required, especially in situations of insulin resistance (IR). Beta-cell mass adaptation can be achieved through either beta-cell proliferation or beta-cell neogenesis, a process that involves de novo beta-cell production from precursor cells. Signals and mechanisms that control adult beta-cell neogenesis and regulate the balance between beta-cell proliferation and/or beta-cell neogenesis still need to be fully deciphered. To do so, we previously developed a mouse model of pancreatic adaptation in response to a severe insulin resistance induced by a chronic glucocorticoid (GC) treatment. We observed a massive insulin production due to beta-cell adaptation by both proliferation and neogenesis. In the present study, we aimed at further characterizing beta-cell adaptation in response to mild or severe IR by studying various GC doses, along with other pharmacological or genetic models of IR. Further, we characterized the impact of aging on pancreatic adaptation in response to GC-induced IR. Finally, we precisely quantified adult beta-cell neogenesis by developing an original 3D method of beta-cell mass analysis in toto after organ clearing. MethodsGlucose metabolism, insulin secretion and pancreatic beta-cell adaptation were studied in mice rendered IR either by adipose tissue specific invalidation of SEIPIN, by chronic treatment with the insulin receptor antagonist S961 or by chronic treatment with several doses of GC both in young and aged mice. Moreover, we developed and used an unbiased-3D analysis of beta cells on whole cleared pancreas. ResultsWe demonstrated that beta-cell neogenesis - reflected by an increase in islet density - is constantly observed in response to genetically- or pharmacology-induced (S961 or GC) IR. Next, we observed that pancreatic adaptation mechanisms are closely defined by the level of IR. Indeed, mild IR induced by low dose of GC resulted in functional adaptation solely, while more severe IR induced by higher doses of GC resulted in an increase in both islet density and mean islet size, reflecting beta-cell neogenesis and proliferation, respectively. Then, we showed that in older mice, beta-cell adaptation through neogenesis is preserved in response to IR. Finally, using a new and unbiased 3D analysis, we confirmed the increase in islet density and mean islet size after GCs treatment. Conclusions/interpretationOur results present evidence that beta-cell neogenesis is a preferential mechanism of pancreatic adaptation to increase insulin secretion in response to IR in mice. Moreover, aging does not preclude beta-cell neogenesis, suggesting that it could be triggered in elderly to compensate for IR. Finally, our innovative technique of 3D analysis of whole pancreas confirms the existence of adult beta-cell neogenesis and offers a new avenue to study islet cells and pancreas adaptation. Research in contextO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LIInsulin resistance can be compensated by improved insulin secretion and increased beta-cell mass. C_LIO_LINew beta cells can be formed in the pancreas of adult mice through the differentiation of precursors, a process known as neogenesis. C_LIO_LIWe previously demonstrated that glucocorticoid (GC) -induced insulin resistance leads to enhanced beta-cell proliferation and neogenesis. C_LI What is the key question?O_LIIs adaptive beta-cell neogenesis specific to GC-induced insulin resistance and persists in old mice ? C_LI What are the new findings?O_LIInsulin resistance, either genetically- or drug-induced, is a key driver to induce adaptive beta-cell neogenesis in the mouse pancreas. C_LIO_LIAging does not prevent the induction of beta-cell neogenesis in response to insulin resistance. C_LIO_LIThree-dimension analysis on cleared pancreas confirms beta-cell neogenesis in mouse models of GC-induced insulin resistance. C_LI How might this impact on clinical practice in the foreseeable future?O_LIThe mouse model of adaptive beta-cell neogenesis will be helpful to define new therapeutic targets to induce the formation of new beta cells and treat diabetes. C_LI

physiology↗