Leptin signaling in the carotid body: mechanisms and consequences

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Obesity causes multiple complications including hypertension, type 2 diabetes and sleep disordered breathing (SDB), which contribute to cardiovascular morbidity and mortality. Obesity and its complications are linked to increased activity of the sympathetic nervous system (SNS). The carotid bodies (CB) modulate afferent input to the SNS and have been identified as a potential therapeutic target. CB denervation abolished hypertension and hyperglycemia. The robust CB hypoxic chemoreflex has been implicated in respiratory instability and increased loop gain, one of the cardinal traits of SDB. Our long-term goal is to develop novel therapeutics, which will treat hypertension, diabetes and SDB in obesity by modulating the CB activity. During the first funding period of the award, we discovered a unique pathway by which adipose-tissue-produced hormone leptin acts in CB to increase the hypoxic chemoreflex and induce hypertension. Leptin interacts with the long isoform of leptin receptor, LEPRb, on CB type I cells to activate transient receptor potential melastatin 7 (TRPM7) cation channel. This mechanism increases carotid sinus nerve (CSN) activity and the chemoreflex, which ultimately leads to SDB, hypertension and perturbations of glucose metabolism. We developed novel molecular approaches to interrogate the CB leptin-TRPM7 pathway targeting Leprb gene expression, signaling via the JAK/STAT3 and PI3K and targeting leptin resistance induced by suppressor of cytokine signaling-3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B). The overarching hypothesis of this proposal is that, in DIO, leptin acts via TRPM7 in the CB type I cells to increase the hypoxic chemoreflex and CSN activity leading to SNS activation, hypertension, diabetes, and SDB, all of which can be treated by our novel TRPM7 blocker. We will examine the role of the leptin-TRPM7 axis in CB in obesity-induced hypertension, diabetes (Specific Aim 1) and SDB (Specific Aim 2) in mice with diet-induced obesity (DIO). We propose that leptin acts via CB TRPM7 to increase SNS activity inducing hypertension and hyperglycemia and to augment the chemoreflex causing SDB, which will be abolished by (A) Leprb shRNA and (B) Trpm7 shRNA applied to CB; (C) TRPM7 blocker FTY720 in a novel extended release formulation administered to the CB; and that (D) LEPRb blocker Allo-aca and TRPM7 blocker FTY720 administered to CB will decrease CSN, phrenic, splanchnic and renal sympathetic nerve activity. Specific Aim 3 will examine the cellular and molecular regulation of LEPRb-TRPM7 signaling in CB of DIO mice. We propose that in DIO, high leptin levels increase TRPM7 activity in CB glomus cells (A) acutely via JAK2/PI3K signaling; (B) chronically by increasing Leprb and Trpm7 gene expression via the JAK2/STAT3 pathway. We will employ state-of-the-art techniques including in vivo manipulation of gene expression in CB with viral vectors, FTY720 hydrogel molecular assembly, telemetry recording, sleep studies with quantified analysis of breathing, CB type I cell patch clamping and sympathetic nerve recording. Our translational proposal will identify potential novel treatment of hypertension, diabetes and SDB in obesity.