Leptin enhances hypothalamic lactate dehydrogenase A (LDHA)-dependent glucose sensing to lower glucose production in high-fat-fed rats

Abstract

The responsiveness of glucose sensing per se to regulate whole-body glucose homeostasis is dependent on the ability of a rise in glucose to lower hepatic glucose production and increase peripheral glucose uptake in vivo In both rodents and humans, glucose sensing is lost in diabetes and obesity, but the site(s) of impairment remains elusive. Here, we first report that short-term high-fat feeding disrupts hypothalamic glucose sensing to lower glucose production in rats. Second, leptin administration into the hypothalamus of high-fat-fed rats restored hypothalamic glucose sensing to lower glucose production during a pancreatic (basal insulin)-euglycemic clamp and increased whole-body glucose tolerance during an intravenous glucose tolerance test. Finally, both chemical inhibition of hypothalamic lactate dehydrogenase (LDH) (achieved via hypothalamic LDH inhibitor oxamate infusion) and molecular knockdown of LDHA (achieved via hypothalamic lentiviral LDHA shRNA injection) negated the ability of hypothalamic leptin infusion to enhance glucose sensing to lower glucose production in high fat-fed rats. In summary, our findings illustrate that leptin enhances LDHA-dependent glucose sensing in the hypothalamus to lower glucose production in high-fat-fed rodents in vivo.

Keywords: LDHA; brain; glucose; glucose metabolism; glucose production; glucose sensing; hypothalamus; leptin.

Figure 1.

High-fat feeding impairs hypothalamic glucose sensing. A, experimental protocol. B, cumulative food intake. *, p < 0.05 compared with regular chow (RC)–fed. Body weight (C), fat and lean mass (D), and free water and total water mass (E) of HFD (n = 7)- versus RC (n = 5)-fed rats are shown. F, glucose infusion rate. G, glucose production in basal (white bars) and clamp (black bars) conditions. H, glucose uptake during the clamps. n = 7 for RC-MBH saline, n = 6 for RC-MBH glucose, n = 7 for HFD-MBH saline, and n = 7 for HFD-MBH glucose. Error bars represent S.E. *, p < 0.05 compared with RC-saline, HFD-saline, and HFD-glucose. LV, lentivirus.

Figure 2.

Leptin enhances hypothalamic glucose sensing. Glucose infusion rate (A), glucose production in basal (white bars) and clamp (black bars) conditions (B), and glucose uptake during the clamps (C) (n = 7 per group) are shown. Error bars represent S.E. *, p < 0.05 compared with HFD-MBH glucose. D, experimental protocol for the i.v. GTT experiments on HFD rats that received MBH saline (n = 6) or MBH leptin (n = 9). E, percent change in plasma glucose levels during i.v. GTT and integrated area under the curve (AUC). Error bars represent S.E. †, p < 0.05 compared with HFD-MBH saline.

Figure 3.

Chemical inhibition of hypothalamic LDH negates leptin's impact on glucose sensing. A, schematic of hypothesis. Glucose infusion rate (B), glucose production in basal (white bars) and clamp (black bars) conditions (C), and glucose uptake during the clamps (D) (n = 7 per group) are shown. Error bars represent S.E. *, p < 0.05 compared with all other groups except leptin + oxamate; †, p < 0.05 compared with all other groups except leptin + glucose.

Figure 4.

Molecular knockdown of hypothalamic LDH negates leptin's impact on glucose sensing. A, representative Western blot of LDHA and LDHB in the MBH of rats that received MBH injections of either MM (n = 4) or LDHA shRNA lentivirus (n = 5). Quantification of LDHA or LDHB levels normalized to β-tubulin expressed as -fold change over MM is shown below. Error bars represent S.E. *, p < 0.05 compared with MM. Glucose infusion rate (B), glucose production in basal (white bars) and clamp (black bars) conditions (C), and glucose uptake during the clamps (D) (n = 7 per group) are shown. Error bars represent S.E. *, p < 0.05 compared with RC-MBH saline and RC-MBH glucose + LDHA shRNA; †, p < 0.05 compared with HFD-MBH saline + MM, HFD-MBH glucose + MM, HFD-MBH glucose + LDHA shRNA, and HFD-MBH glucose + leptin + LDHA shRNA.