Rationale: We recently demonstrated that the 'Metabesity' factor HMG20A regulates islet beta-cell functional maturity and adaptation to physiological stress such as pregnancy and pre-diabetes. HMG20A also dictates central nervous system (CNS) development via inhibition of the LSD1-CoREST complex but its expression pattern and function in adult brain remains unknown. Herein we sought to determine whether HMG20A is expressed in the adult CNS, specifically in hypothalamic astrocytes that are key in glucose homeostasis and whether similar to islets, HMG20A potentiates astrocyte function in response to environmental cues. Methods: HMG20A expression profile was assessed by quantitative PCR (QT-PCR), Western blotting and/or immunofluorescence in: 1) the hypothalamus of mice exposed or not to either a high-fat diet or a high-fat high-sucrose regimen, 2) human blood leukocytes and adipose tissue obtained from healthy or diabetic individuals and 3) primary mouse hypothalamic astrocytes exposed to either high glucose or palmitate. RNA-seq and cell metabolic parameters were performed on astrocytes treated or not with a siHMG20A. Astrocyte-mediated neuronal survival was evaluated using conditioned media from siHMG20A-treated astrocytes. The impact of ORY1001, an inhibitor of the LSD1-CoREST complex, on HMG20A expression, reactive astrogliosis and glucose metabolism was evaluated in vitro and in vivo in high-fat high-sucrose fed mice. Results: We show that Hmg20a is predominantly expressed in hypothalamic astrocytes, the main nutrient-sensing cell type of the brain. HMG20A expression was upregulated in diet-induced obesity and glucose intolerant mice, correlating with increased transcript levels of Gfap and Il1b indicative of inflammation and reactive astrogliosis. Hmg20a transcript levels were also increased in adipose tissue of obese non-diabetic individuals as compared to obese diabetic patients. HMG20A silencing in astrocytes resulted in repression of inflammatory, cholesterol biogenesis and epithelial-to-mesenchymal transition pathways which are hallmarks of reactive astrogliosis. Accordingly, HMG20A depleted astrocytes exhibited reduced mitochondrial bioenergetics and increased susceptibility to apoptosis. Neuron viability was also hindered in HMG20A-depleted astrocyte-derived conditioned media. ORY1001 treatment rescued expression of reactive astrogliosis-linked genes in HMG20A ablated astrocytes while enhancing cell surface area, GFAP intensity and STAT3 expression in healthy astrocytes, mimicking the effect of HMG20A. Furthermore, ORY1001 treatment protected against obesity-associated glucose intolerance in mice correlating with a regression of hypothalamic HMG20A expression, indicative of reactive astrogliosis attenuation with improved health status. Conclusion: HMG20A coordinates the astrocy...

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Rationale: We recently demonstrated that the Metabesity factor HMG20A regulates islet beta-cell functional maturity and adaptation to physiological stress such as pregnancy and pre-diabetes. HMG20A also dictates central nervous system (CNS) development via inhibition of the LSD1/CoREST complex but its expression pattern and function in the adult brain remains unknown. Herein we sought to determine whether HMG20A is expressed in the adult CNS, specifically in hypothalamic astrocytes that are key in glucose homeostasis and whether similar to islets, HMG20A potentiates astrocyte function in response to environmental cues. Methods: HMG20A expression profile was assessed by quantitative PCR (RT-PCR) and/or immunofluorescence in 1) the hypothalamus of mice exposed or not to a high-fat diet, 2) human blood leukocytes and adipose tissue obtained from healthy or diabetic individuals 3) primary mouse hypothalamic astrocytes exposed to either high glucose or palmitate. To investigate the function and regulatory mechanism of HMG20A, RNA-seq and cell metabolic parameters were performed on astrocytes treated or not with a siHMG20A. The regulatory function of HMG20A on astrogliosis was also assessed pharmacologically using ORY1001. Astrocyte-mediated neuronal survival was evaluated using conditioned media from siHMG20A-treated astrocytes. Results: We show that Hmg20a is predominantly expressed in hypothalamic astrocytes, the main nutrient-sensing cell type of the brain. Hmg20A expression was upregulated in diet-induced obesity and glucose-intolerant mice, correlating with increased transcript levels of Gfap and Il1b indicative of inflammation and astrogliosis. Expression levels were also increased in adipose tissue of obese non-diabetic individuals as compared to obese diabetic patients. HMG20A silencing in astrocytes resulted in repression of inflammatory, cholesterol biogenesis and epithelial-to-mesenchymal transition pathways with a concomitant increase in apoptosis and reduced mitochondrial bioenergetics. Motoneuron viability was also hindered in HMG20A-depleted astrocyte-derived conditioned media. Astrogliosis was induced using ORY1001, a pharmacological inhibitor of the LSD1/CoREST complex, mimicking the effect of HMG20A. Conclusion: HMG20A coordinates the astrocyte polarization state. Under physiological pressure such as obesity and insulin resistance that induces low-grade inflammation, HMG20A expression is increased to induce astrogliosis in an attempt to preserve the neuronal network and glucose homeostasis. Nonetheless, a chronic metabesity state or functional mutations will result in lower levels of HMG20A, failure to promote astrogliosis and increase the susceptibility of neurons to stress-mediated apoptosis. Such effects could be therapeutically reversed by ORY1001-induced astrogliosis.

We have previously described a role of LRH-1/NR5A2 in islet morphogenesis during postnatal development and reported that the treatment with BL001, an agonist of LRH-1/NR5A2, protects islets against-stress induced apoptosis and reverts hyperglycemia in 3 mouse models of Type 1 Diabetes Mellitus (T1DM). Islet transcriptome profiling revealed that most differentially expressed genes after BL001 treatment are involved in immunomodulation, among them, the increase in PTGS2/COX2 expression. Herein, we dissected the cellular and molecular branches of the BL001/LRH-1/NR5A2 signalling axis in order to chart the mode of action confering beta cell protection and hyperglycaemia reversion. We found that constitutive LRH-1/NR5A2 ablation within the insulin expression domain (RIP-Cre mouse model) caused a significant beta cell mass reduction characterized by blunted proliferation correlating with animal growth retardation, weight loss and hypoglycemia, leading to lethality before weaning. Using an inducible approach (pdx1PBCreER™ mouse model), specific deletion of LRH-1/NR5A2 in adult beta cells abolished the anti diabetic effect of BL001 in streptozotocin treated mice, correlating with complete beta-cell mass destruction. Additionally, BL001 induced Ptgs2 expression, was blunted in islets lacking LRH-1/NR5A2. The combined BL001/cytokine treatment did not further stimulate Ptgs2 expression above levels detected with cytokine alone yet secreted PGE2 levels were increased 5-fold. Inactivation of PTGS2 blunted induction of the target and its product PGE2 in islets treated with cytokines alone or with BL001. Importantly, PTGS2 inactivated islets were refractory to the BL001 protective effect under cytokine attack as evidenced by increased Bax expression levels, cytochrome C release and cleaved PARP. The PTGER1 antagonist ONO-8130, but not the PTGER4 antagonist L-161,982, negated BL001-mediated islet survival. Our results establish that the beneficial properties of BL001 against stress-induced cell death are specifically conveyed by LRH-1/NR5A2 activation in beta cells and downstream stimulation of the PTGS2-PGE2/PTGER1 signalling axis.