Endogenous leptin signaling in the caudal nucleus tractus solitarius and area postrema is required for energy balance regulation

Abstract

Medial nucleus tractus solitarius (mNTS) neurons express leptin receptors (LepRs), and intra-mNTS delivery of leptin reduces food intake and body weight. Here, the contribution of endogenous LepR signaling in mNTS neurons to energy balance control was examined. Knockdown of LepR in mNTS and area postrema (AP) neurons of rats (LepRKD) via adeno-associated virus short hairpin RNA-interference (AAV-shRNAi) resulted in significant hyperphagia for chow, high-fat, and sucrose diets, yielding increased body weight and adiposity. The chronic hyperphagia of mNTS/AP LepRKD rats is likely mediated by a reduction in leptin potentiation of gastrointestinal satiation signaling, as LepRKD rats showed decreased sensitivity to the intake-reducing effects of cholecystokinin. LepRKD rats showed increased basal AMP-kinase activity in mNTS/AP micropunches, and pharmacological data suggest that this increase provides a likely mechanism for their chronic hyperphagia. Overall these findings demonstrate that LepRs in mNTS and AP neurons are required for normal energy balance control.

Figure 1

Representative immunofluorescent analysis showing the extent of AAV-shCtrl (A) and AAV-LepR (B) spread, with EGFP-expressing neurons being identified in nuclei that contain the LepR: medial nucleus tractus solitarius (mNTS) and area postrema (AP). EGFP-expressing neurons are also found in non-LepR-expressing nuclei: dorsal motor nucleus of the vagus (DMV), dorsolateral NTS (SolDL) and solitary commissural (SolC). cc = central canal. (C) Representative qPCR reveals significant suppression in LepR mRNA in mNTS/AP micropunched tissue for AAV-LepR treated rats compared to AAV-shCtrl rats. * = P< 0.05. (D) Daily Kcal intake for LepRKD and shCtrl rats pre- and post-viral delivery while maintained on chow or high fat (HF) diet (60% Kcal from fat). * = P< 0.05 for bracketed weekly averages.

Figure 2

Cumulative body weight of chow-maintained LepRKD and shCtrl rats pre- and post-mNTS/AP directed AAV delivery. * = P< 0.05 for bracketed weekly averages. Inset graph shows inguinal and total WAT mass for LepRKD and shCtrl rats. * = P<0.05.

Figure 3

(A) Cumulative 15% sucrose intake following IP injection of CCK (3μg/kg) or vehicle (0.9% saline) for LepRKD and shCtrl rats pre- and 4 weeks-post mNTS-directed AAV delivery. * = P< 0.05. (B) LepRKD rats showed increased pAMPKα2 levels in mNTS/AP micropunched tissue compared to shCtrl rats under ad libitum fed conditions. Representative immunoblots for total AMPK and pAMPKα2 are shown. Relative pAMPKα2 = the ratio of pAMPKα2 to total AMPK. * = P< 0.05. (C) Cumulative chow intake for LepRKD and shCtrl rats following 4^th icv delivery of compound C (15μg) or vehicle (DMSO). * = P< 0.05.