Leptin Receptor Expression in GABAergic Cells is Not Sufficient to Normalize Metabolism and Reproduction in Mice

Abstract

Previous studies indicate that leptin receptor (LepR) expression in GABAergic neurons is necessary for the biological effects of leptin. However, it is not clear whether LepR expression only in GABAergic neurons is sufficient to prevent the metabolic and neuroendocrine imbalances caused by LepR deficiency. In the present study, we produced mice that express the LepR exclusively in GABAergic cells (LepR VGAT mice) and compared them to wild-type (LepR +/+) and LepR-deficient (LepR Null/Null) mice. Although LepR VGAT mice showed a pronounced reduction in body weight and fat mass, as compared to LepR Null/Null mice, male and female LepR VGAT mice exhibited an obese phenotype in comparison to LepR +/+ mice. Food intake was normalized in LepR VGAT mice; however, LepR VGAT mice still exhibited lower energy expenditure in both sexes and reduced ambulatory activity in the females, compared to LepR +/+ mice. The acute anorexigenic effect of leptin and hedonic feeding were normalized in LepR VGAT mice despite the hyperleptinemia they present. Although LepR VGAT mice showed improved glucose homeostasis, as compared to LepR Null/Null mice, both male and female LepR VGAT mice exhibited insulin resistance. In contrast, LepR expression only in GABAergic cells was sufficient to normalize the density of AgRP and α-MSH immunoreactive fibers in the paraventricular nucleus of the hypothalamus. However, LepR VGAT mice exhibited reproductive dysfunctions, including subfertility in males and alterations in the estrous cycle of females. Taken together, our findings indicate that LepR expression in GABAergic cells, although critical to the physiology of leptin, is insufficient to normalize several metabolic aspects and the reproductive function in mice.

Glutamate neurotransmission from leptin receptor cells is required for typical puberty and reproductive function in female mice

“…Due to the fundamental role of reproduction for species survival, redundancy of neural pathways is expected, and developmental adaptations may have occurred in those studies. Of note, a recent study showed that re-expression of LepRb only in GABAergic cells is not sufficient for restoration of reproduction in otherwise LepRb null mice, emphasizing the need for other populations (Quaresma et al, 2021). Similarly, alternative metabolic signals may take over control in the absence of leptin signaling in this specific pathway (Hill et al, 2010; Hill and Elias, 2018).…”

Pattern of gonadotropin secretion along the estrous cycle of C57BL/6 female mice

“…In‐house sensitive sandwich enzyme‐linked immunosorbent assays (ELISA) were adapted from published protocols to determine plasma LH (Brown et al, 2019; Quaresma et al, 2021) and FSH (De Paula et al, 2021; Ongaro et al, 2021) levels. A 96‐well high‐binding plate (9018, Corning) was coated with 50 μl of monoclonal mouse anti‐bovine LH beta subunit antibody (1:2500; Pablo Ross, UC Davis, 518B7; RRID: AB_2756886) or polyclonal guinea pig anti‐mouse FSH antibody (1:20,000; AFP1760191, NIDDK‐NHPP; RRID: AB_2665512) overnight at 4°C.…”

“…In-house sensitive sandwich enzyme-linked immunosorbent assays (ELISA) were adapted from published protocols to determine plasma LH (Brown et al, 2019;Quaresma et al, 2021) for 2 h at room temperature (RT). The standard curve consisted of a twofold serial dilution of mouse recombinant LH (AFP-5306A, NIDDK-NHPP) or rat recombinant FSH (rFSH-RP-2, AFP4621B, NIDDK-NHPP) in 0.2% bovine serum albumin (BSA) PBS-T from 0.00976 to 5 ng/ml and 0.03125 to 16 ng/ml, respectively.…”

A critical update on the leptin‐melanocortin system

“…Indeed, deleting Lepr selectively in GABAergic neurons ( Slc32a1 ( Vgat )‐Cre:: Lepr flox/flox ) was shown to increase food intake and body weight close to the phenotype of global Lepr KO mice (Vong et al, 2011). Based on these results, a recent study took a complementary approach to determine whether Lepr re‐expression only in GABAergic neurons ( Slc32a1 ‐Cre:: Lepr TB/TB ) was sufficient to normalize the severe obesity phenotype of global Lepr KO mice (Quaresma et al, 2021). Lepr expression exclusively in GABAergic cells induced a drastic reduction in body weight and fat mass compared to mice globally deficient for Lepr‐b ( Lepr TB/TB ) but could not quite normalize these parameters to control levels.…”

“…In fact, Lepr expression in GABAergic neurons was sufficient to completely normalize food intake, but only partially restored the reduced oxygen consumption of Lepr TB/TB mice. Plasma leptin, insulin, and glucose levels were also not completely rescued (Quaresma et al, 2021). This partial recovery suggests the involvement of many neuronal populations mediating specific effects of leptin, rather than one leptin‐responsive neuronal population mediating all of leptin's effects.…”