LRH-1 agonism favours an immune-islet dialogue which protects against diabetes mellitus.

Type 1 diabetes mellitus (T1DM) is due to the selective destruction of islet beta cells by immune cells. Current therapies focused on repressing the immune attack or stimulating beta cell regeneration still have limited clinical efficacy. Therefore, it is timely to identify innovative targets to dampen the immune process, while promoting beta cell survival and function. Liver receptor homologue-1 (LRH-1) is a nuclear receptor that represses inflammation in digestive organs, and protects pancreatic islets against apoptosis. Here, we show that BL001, a small LRH-1 agonist, impedes hyperglycemia progression and the immune-dependent inflammation of pancreas in murine models of T1DM, and beta cell apoptosis in islets of type 2 diabetic patients, while increasing beta cell mass and insulin secretion. Thus, we suggest that LRH-1 agonism favors a dialogue between immune and islet cells, which could be druggable to protect against diabetes mellitus.

The type 2 diabetes-associated HMG20A gene is mandatory for islet beta cell functional maturity.

HMG20A (also known as iBRAF) is a chromatin factor involved in neuronal differentiation and maturation. Recently small nucleotide polymorphisms (SNPs) in the HMG20A gene have been linked to type 2 diabetes mellitus (T2DM) yet neither expression nor function of this T2DM candidate gene in islets is known. Herein we demonstrate that HMG20A is expressed in both human and mouse islets and that levels are decreased in islets of T2DM donors as compared to islets from non-diabetic donors. In vitro studies in mouse and human islets demonstrated that glucose transiently increased HMG20A transcript levels, a result also observed in islets of gestating mice. In contrast, HMG20A expression was not altered in islets from diet-induced obese and pre-diabetic mice. The T2DM-associated rs7119 SNP, located in the 3' UTR of the HMG20A transcript reduced the luciferase activity of a reporter construct in the human beta 1.1E7 cell line. Depletion of Hmg20a in the rat INS-1E cell line resulted in decreased expression levels of its neuronal target gene NeuroD whereas Rest and Pax4 were increased. Chromatin immunoprecipitation confirmed the interaction of HMG20A with the Pax4 gene promoter. Expression levels of Mafa, Glucokinase, and Insulin were also inhibited. Furthermore, glucose-induced insulin secretion was blunted in HMG20A-depleted islets. In summary, our data demonstrate that HMG20A expression in islet is essential for metabolism-insulin secretion coupling via the coordinated regulation of key islet-enriched genes such as NeuroD and Mafa and that depletion induces expression of genes such as Pax4 and Rest implicated in beta cell de-differentiation. More importantly we assign to the T2DM-linked rs7119 SNP the functional consequence of reducing HMG20A expression likely translating to impaired beta cell mature function.

Increased prepubertal body weight enhances leptin sensitivity in proopiomelanocortin and neuropeptide y neurons before puberty onset in female rats.

Pubertal onset may be advanced by obesity, with leptin potentially acting as a permissive factor. We hypothesized that having increased body weight (BW) prepubertally affects the ability of leptin to activate intracellular signaling pathways and modulate the expression of hypothalamic neuropeptides involved in reproduction and metabolism. Because being raised in small litters (SLs) tends to increase BW at weaning, female rats were raised in litters of 4 or large litters (LLs) of 12 pups. Leptin (3 µg/g BW) or vehicle (saline) was injected sc at postnatal day (PND) 21 and 30. Rats raised in SLs weighed more at both ages, but relative visceral and subcutaneous fat was increased only on PND21. Serum leptin levels were not different at PND21 or PND30. At PND21, key elements of intracellular leptin signaling (phosphorylated signal transducer and activator of transcription 3 and phosphorylated Akt [p-Akt]) were lower in SL than in LL rats. Leptin injection stimulated phosphorylated signal transducer and activator of transcription 3 in both groups, with a greater increase in LL, whereas p-Akt rose only in SL rats. At PND30, basal leptin signaling did not differ between LL and SL rats. Leptin activation of Akt was similar at 45 minutes, but at 2 hours p-AKT levels were higher in SL than in LL rats, as was the decrease in neuropeptide Y mRNA and increase in pro-opiomelanocortin mRNA levels. No change in the reproductive axis was found. Thus, being raised in SLs increases BW and visceral body fat content, fails to increase plasma leptin concentrations, and increases the leptin responsiveness of both neuropeptide Y and pro-opiomelanocortin cells in the prepubertal hypothalamus.

Hypothalamic PGC-1α protects against high-fat diet exposure by regulating ERα.

High-fat diets (HFDs) lead to obesity and inflammation in the central nervous system (CNS). Estrogens and estrogen receptor α (ERα) protect premenopausal females from the metabolic complications of inflammation and obesity-related disease. Here, we demonstrate that hypothalamic PGC-1α regulates ERα and inflammation in vivo. HFD significantly increased palmitic acid (PA) and sphingolipids in the CNS of male mice when compared to female mice. PA, in vitro, and HFD, in vivo, reduced PGC-1α and ERα in hypothalamic neurons and astrocytes of male mice and promoted inflammation. PGC-1α depletion with ERα overexpression significantly inhibited PA-induced inflammation, confirming that ERα is a critical determinant of the anti-inflammatory response. Physiologic relevance of ERα-regulated inflammation was demonstrated by reduced myocardial function in male, but not female, mice following chronic HFD exposure. Our findings show that HFD/PA reduces PGC-1α and ERα, promoting inflammation and decrements in myocardial function in a sex-specific way.

The opposing effects of ghrelin on hypothalamic and systemic inflammatory processes are modulated by its acylation status and food intake in male rats.

Ghrelin is an endogenous hormone that stimulates appetite and adipose tissue accrual. Both the acylated (AG) and non-acylated (DAG) isoforms of this hormone are also reported to exert anti-inflammatory and protective effects systemically and in the central nervous system. As inflammatory processes have been implicated in obesity-associated secondary complications, we hypothesized that this natural appetite stimulator may protect against negative consequences resulting from excessive food intake. Adult male Wistar rats were treated icv (5 µg/day) with AG, DAG, the ghrelin mimetic GH-releasing peptide (GHRP)-6, AG, and pair-fed with controls (AG-pf) or saline for 14 days. Regardless of food intake AG increased visceral adipose tissue (VAT) and decreased circulating cytokine levels. However, AG reduced cytokine production in VAT only in rats fed ad libitum. Hypothalamic cytokine production was increased in AG-treated rats fed ad libitum and by DAG, but intracellular inflammatory signaling pathways associated with insulin and leptin resistance were unaffected. Gliosis was not observed in response to any treatment as glial markers were either reduced or unaffected. AG, DAG, and GHRP-6 stimulated production of hypothalamic insulin like-growth factor I that is involved in cell protective mechanisms. In hypothalamic astrocyte cell cultures AG decreased tumor necrosis factorα and DAG decreased interleukin-1ß mRNA levels, suggesting direct anti-inflammatory effects on astrocytes. Thus, whereas ghrelin stimulates food intake and weight gain, it may also induce mechanisms of cell protection that help to detour or delay systemic inflammatory responses and hypothalamic gliosis due to excess weight gain, as well as its associated pathologies.

Hypothalamic inflammation without astrogliosis in response to high sucrose intake is modulated by neonatal nutrition in male rats.

Hypothalamic inflammation and gliosis are proposed to participate in the pathogenesis of high-fat diet-induced obesity. Because other factors and nutrients also induce weight gain and adiposity, we analyzed the inflammatory and glial responses to a sucrose (S)-enriched diet. Neonatal overnutrition (NON) exacerbates weight gain in response to metabolic challenges; thus, we compared the inflammatory response of male Wistar rats with NON (4 pups/litter) and controls (12 pups/litter) to increased S intake. At weaning rats received water or a 33% sucrose solution and normal chow ad libitum for 2 months. Sucrose increased serum IL-1ß and -6 and hypothalamic IL-6 mRNA levels in NON and TNFα mRNA levels in control and NON rats, whereas NON alone had no effect. The astrocyte marker glial fibrillary acidic protein was increased by NON but decreased by S. This was associated with hypothalamic nuclei specific changes in glial fibrillary acidic protein-positive cell number and morphology. Sucrose increased the number of microglia and phosphorylation of inhibitor of -κB and c-Jun N-terminal kinase in control but not NON rats, with no effect on microglia activation markers. Proteins highly expressed in astrocytes (glutamate, glucose, and lactate transporters) were increased by NON but not S, with no increase in vimentin expression in astrocytes, further suggesting that S-induced adiposity is not associated with hypothalamic astrogliosis. Hence, activation of hypothalamic inflammatory processes and gliosis depend not only on weight gain but also on the diet inducing this weight gain and the early nutritional status. These diverse inflammatory processes could indicate a differential disposition to obesity-induced pathologies.