Probes for INS

Leptin contributes to the control of resting metabolic rate (RMR) and blood pressure (BP) through its actions in the arcuate nucleus (ARC). The renin-angiotensin system (RAS) and angiotensin AT1 receptors within the brain are also involved in the control of RMR and BP, but whether this regulation overlaps with leptin's actions is unclear. Here, we have demonstrated the selective requirement of the AT1A receptor in leptin-mediated control of RMR. We observed that AT1A receptors colocalized with leptin receptors (LEPRs) in the ARC. Cellular coexpression of AT1A and LEPR was almost exclusive to the ARC and occurred primarily within neurons expressing agouti-related peptide (AgRP). Mice lacking the AT1A receptor specifically in LEPR-expressing cells failed to show an increase in RMR in response to a high-fat diet and deoxycorticosterone acetate-salt (DOCA-salt) treatments, but BP control remained intact. Accordingly, loss of RMR control was recapitulated in mice lacking AT1A in AgRP-expressing cells. We conclude that angiotensin activates divergent mechanisms to control BP and RMR and that the brain RAS functions as a major integrator for RMR control through its actions at leptin-sensitive AgRP cells of the ARC.

Sonic hedgehog (SHH) is an essential morphogenetic signal dictating cell fate decisions in several developing organs in mammals. In vitrodata suggest that SHH is required to specify LHX3+/LHX4+ Rathke's pouch (RP) progenitor identity. However, in vivo studies have failed to reveal such a function, supporting instead, a critical role for SHH in promoting proliferation of these RP progenitors and for differentiation of pituitary cell types. Here, we have used a genetic approach to demonstrate that activation of the SHH pathway is necessary to induce LHX3+/LHX4+ RP identity in mouse embryos. First, we show that conditional deletion of Shh in the anterior hypothalamus results in a fully penetrant phenotype characterised by a complete arrest of RP development, with lack of Lhx3/Lhx4 expression in RP epithelium at 9.0 dpc (days post coitum) and total loss of pituitary tissue by 12.5 dpc. Conversely, over-activation of the SHH pathway by conditional deletion of Ptch1 in RP progenitors leads to severe hyperplasia and enlargement of the Sox2+ve stem cell compartment by the end of gestation.

The unique mental abilities of humans are rooted in the immensely expanded and folded neocortex, which reflects the expansion of neural progenitors, especially basal progenitors including basal radial glia (bRGs) and intermediate progenitor cells (IPCs). We found that constitutively active Sonic hedgehog (Shh) signaling expanded bRGs and IPCs and induced folding in the otherwise smooth mouse neocortex, whereas the loss of Shh signaling decreased the number of bRGs and IPCs and the size of the neocortex. SHH signaling was strongly active in the human fetal neocortex but Shh signaling was not strongly active in the mouse embryonic neocortex, and blocking SHH signaling in human cerebral organoids decreased the number of bRGs. Mechanistically, Shh signaling increased the initial generation and self-renewal of bRGs and IPC proliferation in mice and the initial generation of bRGs in human cerebral organoids. Thus, robust SHH signaling in the human fetal neocortex may contribute to bRG and IPC expansion and neocortical growth and folding.

Central activation of fibroblast growth factor (FGF) receptors regulates peripheral glucose homeostasis and reduces food intake in preclinical models of obesity and diabetes. The current work was undertaken to advance our understanding of the receptor expression, as sites of ligand action by FGF19, FGF21, and FGF1 in the mammalian brain remains unresolved. Recent advances in automated RNAscope in situ hybridization and droplet digital PCR (ddPCR) technology allowed us to interrogate central FGFR/beta klotho (Klb) system at the cellular level in the mouse, with relevant comparisons to nonhuman primate and human brain. FGFR1-3 gene expression was broadly distributed throughout the CNS in Mus musculus, with FGFR1 exhibiting the greatest heterogeneity. FGFR4 expression localized only in the medial habenula and subcommissural organ of mice. Likewise, Klb mRNA was restricted to the suprachiasmatic nucleus (SCh) and select midbrain and hindbrain nuclei. ddPCR in the rodent hypothalamus confirmed that, although expression levels are indeed low for Klb, there is nonetheless a bonafide subpopulation of Klb+ cells in the hypothalamus. In NHP and human midbrain and hindbrain, Klb + cells are quite rare, as is expression of FGFR4. Collectively, these data provide the most robust central map of the FGFR/Klb system to date and highlight central regions that may be of critical importance to assess central ligand effects with pharmacological dosing, such as the putative interactions between the endocrine FGFs and FGFR1/Klb, or FGF19 with FGFR4.

Mitochondrial oxidative phosphorylation (OXPHOS) and substrate utilization critically regulate the function of hypothalamic proopiomelanocortin (POMC)-expressing neurons. Here, we demonstrate that inactivation of apoptosis-inducing factor (AIF) in POMC neurons mildly impairs mitochondrial respiration and decreases firing of POMC neurons in lean mice. In contrast, under diet-induced obese conditions, POMC-Cre-specific inactivation of AIF prevents obesity-induced silencing of POMC neurons, translating into improved glucose metabolism, improved leptin, and insulin sensitivity, as well as increased energy expenditure in AIFΔPOMC mice. On a cellular level, AIF deficiency improves mitochondrial morphology, facilitates the utilization of fatty acids for mitochondrial respiration, and increases reactive oxygen species (ROS) formation in POMC neurons from obese mice, ultimately leading to restored POMC firing upon HFD feeding. Collectively, partial impairment of mitochondrial function shifts substrate utilization of POMC neurons from glucose to fatty acid metabolism and restores their firing properties, resulting in improved systemic glucose and energy metabolism in obesity.