The central nervous system control of energy homeostasis: high fat diet induced hypothalamic microinflammation and obesity

Investigating GABA Neuron-Specific Androgen Receptor Knockout in two Hyperandrogenic Models of PCOS

Androgen excess is a hallmark feature of polycystic ovary syndrome (PCOS), the most common form of anovulatory infertility. Clinical and preclinical evidence links developmental or chronic exposure to hyperandrogenism with programming and evoking the reproductive and metabolic traits of PCOS. While critical androgen targets remain to be determined, central GABAergic neurons are postulated to be involved. Here, we tested the hypothesis that androgen signaling in GABAergic neurons is critical in PCOS pathogenesis in 2 well-characterized hyperandrogenic mouse models of PCOS. Using cre-lox transgenics, GABA-specific androgen receptor knockout (GABARKO) mice were generated and exposed to either acute prenatal androgen excess (PNA) or chronic peripubertal androgen excess (PPA). Females were phenotyped for reproductive and metabolic features associated with each model and brains of PNA mice were assessed for elevated GABAergic input to gonadotropin-releasing hormone (GnRH) neurons. Reproductive and metabolic dysfunction induced by PPA, including acyclicity, absence of corpora lutea, obesity, adipocyte hypertrophy, and impaired glucose homeostasis, was not different between GABARKO and wild-type (WT) mice. In PNA mice, acyclicity remained in GABARKO mice while ovarian morphology and luteinizing hormone secretion was not significantly impacted by PNA or genotype. However, PNA predictably increased the density of putative GABAergic synapses to GnRH neurons in adult WT mice, and this PNA-induced plasticity was absent in GABARKO mice. Together, these findings suggest that while direct androgen signaling in GABA neurons is largely not required for the development of PCOS-like traits in androgenized models of PCOS, developmental programming of GnRH neuron innervation is dependent upon androgen signaling in GABA neurons.

Hypothalamic FTO promotes high-fat diet-induced leptin resistance in mice through increasing CX3CL1 expression

Long-term consumption of a high-fat diet (HFD) disrupts energy homeostasis and leads to weight gain. The fat mass and obesity-associated (FTO) gene has been consistently identified to be associated with HFD-induced obesity. The hypothalamus is crucial for regulating energy balance, and HFD-induced hypothalamic leptin resistance contributes to obesity. FTO, an N6-methyladenosine (m6A) RNA methylation regulator, may be a key mediator of leptin resistance. However, the exact mechanisms remain unclear. Therefore, the present study aims to investigate the association between FTO and leptin resistance. After HFD or standard diet (SD) feeding in male mice for 22 weeks, m6A-sequencing and western blotting assays were used to identify target genes and assess protein level, and molecular interaction changes. CRISPR/Cas9 gene knockout system was employed to investigate the potential function of FTO in leptin resistance and obesity. Our data showed that chemokine (C-X3-C motif) ligand 1 (CX3CL1) was a direct downstream target of FTO-mediated m6A modification. Furthermore, upregulation of FTO/CX3CL1 and suppressor of cytokine signaling 3 (SOCS3) in the hypothalamus impaired leptin-signal transducer and activator of transcription 3 signaling, resulting in leptin resistance and obesity. Compared to wild-type (WT) mice, FTO deficiency in leptin receptor-expressing neurons of the hypothalamus significantly inhibited the upregulation of CX3CL1 and SOCS3, and partially ameliorating leptin resistance under HFD conditions. Our findings reveal that FTO involved in the hypothalamic leptin resistance and provides novel insight into the function of FTO in the contribution to hypothalamic leptin resistance and obesity.

The hypothalamic neuropeptide, QRFP, regulates high fat diet intake in female Long-Evans rats following ovariectomy

Obesity rates in women continue to increase throughout the lifespan and obesity-related comorbidities are prevalent in women in estrogen deficiency. The hypothalamic neuropeptide, QRFP, is an orexigenic peptide that increases the intake of high fat diet (HFD) in female rats and is overexpressed following ovariectomy (OVX). Therefore, the goal of the current series of experiments was to elucidate the effect of QRFP on HFD intake following OVX and determine if QRFP-26 administration in ovariectomized females altered expression of prepro-neuropeptide Y (NPY), agouti-related peptide (AgRP) and proopiomelanocortin (POMC) mRNA in the mediobasal hypothalamus (MBH) and prepro-orexin in the lateral hypothalamus (LH). The intake of HFD was measured following acute administration of QRFP-26 prior to or following estradiol benzoate (EB) treatment in ovariectomized females. When administered prior to EB treatment, QRFP-26 increased HFD intake. EB treatment attenuated the effects of QRFP-26 on HFD intake. Sub-chronic, continuous administration of QRFP-26 increased HFD intake and weight gain following OVX. Subchronic, continuous administration of QRFP siRNA into the 3rd ventricle via osmotic pump decreased prepro-QRFP mRNA levels in the MBH by ∼75%, decreased HFD intake and decreased weight gain following OVX. QRFP-26administration did not alter the expression of prepro-NPY, AgRP or POMC mRNA in the MBH, but decreased prepro-orexin mRNA in the LH of ovariectomized females. Overall, results from these studies support the orexigenic neuropeptide, QRFP, as an important mediator of the ingestion of highly palatable foods and subsequent weight gain in females during estrogen deficiency.

Anti-adiposity and lipid-lowering effects of schisandrol A in diet-induced obese mice

Lignan schisandrol A (SolA) is known to have antioxidant and anti-inflammatory effects. However, the impact of SolA on obesity is poorly understood. To test the hypothesis that SolA has anti-obesity effects, C57BL/6J mice were fed a high-fat diet with or without SolA (0.006%, w/w) for 16 weeks. SolA decreased visceral fat mass (10%) by increasing energy expenditure and upregulating white adipose tissue thermogenic genes mRNA expression. Furthermore, SolA upregulated adipose Lpl mRNA expression and decreased plasma free fatty acid (FFA), triglyceride (TG), apolipoprotein (apo) B, aspartate aminotransferase levels and TG/HDL-cholesterol and apoB/apoA1 ratios as well as hepatic lipid droplets. Increased hepatic β-oxidation and fecal FFA and TG levels were observed in the SolA-supplemented mice, suggesting an association of its lipid-lowering effect with increased hepatic β-oxidation, fecal fat excretion and adipose Lpl. Conclusionally, this study provides evidence on the protective effects of SolA against adiposity, dyslipidemia and nonalcoholic fatty liver disease in obese mice.

EditorialSpecial issue on "Brain-body communication in health and diseases"

Bidirectional interaction between the brain and the peripheral organs plays a key role in homeostasis in the body. Abnormalities in brain-body communication potentially leads to a number of brain diseases, including psychiatric and neurodegenerative disorders. For example, dysbiosis of gut microbiota and altered levels of microbes-derived compounds plays an important role in the pathophysiology of a number of psychiatric disorders and neurodegenerative disorders. Furthermore, depression is the most common psychiatric symptom in patients with physical disorders, including pain and cardiovascular diseases. This special issue brings together current information on the brain-body communication in health and diseases.