Contribution of the co-chaperone FKBP51 in the ventromedial hypothalamus to metabolic homeostasis in male and female mice

Abstract

Objective: Steroidogenic factor 1 (SF1) expressing neurons in the ventromedial hypothalamus (VMH) have been directly implicated in whole-body metabolism and in the onset of obesity. The co-chaperone FKBP51 is abundantly expressed in the VMH and was recently linked to type 2 diabetes, insulin resistance, adipogenesis, browning of white adipose tissue (WAT) and bodyweight regulation.

Methods: We investigated the role of FKBP51 in the VMH by conditional deletion and virus-mediated overexpression of FKBP51 in SF1-positive neurons. Baseline and high fat diet (HFD)-induced metabolic- and stress-related phenotypes in male and female mice were obtained.

Results: In contrast to previously reported robust phenotypes of FKBP51 manipulation in the entire mediobasal hypothalamus (MBH), selective deletion or overexpression of FKBP51 in the VMH resulted in only a moderate alteration of HFD-induced bodyweight gain and body composition, independent of sex.

Conclusions: Overall, this study shows that animals lacking and overexpressing Fkbp5 in Sf1-expressing cells within the VMH display only a mild metabolic phenotype compared to an MBH-wide manipulation of this gene, suggesting that FKBP51 in SF1 neurons within this hypothalamic nucleus plays a subsidiary role in controlling whole-body metabolism.

Keywords: FKBP51; High-fat diet; Mediobasal Hypothalamus; Obesity; SF1; VMH.

Figure 1

Conditional KO of Fkbp5 in Sf1-expressing cells slightly increases BW gain under a HFD challenge in male mice. A Representative RNAscope confocal images of endogenous Fkbp5 mRNA expression in SF1 neurons within the VMH of Sf1^Fkbp5-/- (green panel) and Fkbp5^lox/lox controls (grey panel). B Quantification of the total percentage of Fkbp5 positive cells that co-express Sf1 mRNA revealed significant reduction of Fkbp5 expression in the Sf1^Fkbp5-/- KO line (n = number of analyzed 40x confocal images of either left or right VMH, n_KO = 4, n_Control = 4; 2 animals/genotype). C In a first cohort under SD for 8 weeks and HFD for 21 weeks, Sf1^Fkbp5-/- mice (n = 13) displayed slightly increased HFD-induced BW gain compared to controls (n = 12) which was stable over time but non-significant. D Higher BW was reflected in a significant increase in the ratio of fat to lean mass in Sf1^{Fkbp5 OE} in this cohort compared to controls after 8 weeks on a HFD. Blood glucose levels remained unchanged in the GTT and ITT under chow, which were assessed in a separate cohort (n_{Sf1Fkbp5−/−} = 5; n_Fkbp5lox/lox = 9) (E) and HFD in the first cohort (F). Data are received from mice between 12 and 20 weeks of age and are presented as mean ± SEM. ∗p < 0.05. AUC area under the curve, GTT glucose tolerance test, ITT insulin tolerance test.

Figure 2

Conditional KO of Fkbp5 in Sf1-expressing cells of female mice resembles male metabolic phenotype. A Female Sf1^Fkbp5-/- (n = 9) mice displayed higher HFD-induced weight gain than control Fkbp5^lox/lox (n = 12), thus resemble BW phenotype of the male KO cohort. B Female Sf1^Fkbp5-/- ratio fat to lean mass is higher under a chow diet and after a dietary HFD challenge (15 weeks total). Data are received from mice between 8 and 12 weeks of age and are presented as mean ± SEM. ∗p < 0.05, T < 0.1.

Figure 3

Viral OE of Fkbp5 exclusively in SF1 neurons within the VMH induces a similar metabolic phenotype to the KO under a HFD challenge. A VMH-specific Fkbp5 OE was achieved by bilateral injections of a Cre-dependent human Fkbp5 OE virus into the VMH of Sf1-Cre mice (Sf1^{Fkbp5 OE}; n = 10). Control Sf1-Cre received an eGFP control virus (n = 13). B Representative RNAscope confocal images of Fkbp5 mRNA expression in SF1 neurons within the VMH of Sf1^{Fkbp5 OE} (human Fkbp5; upper orange panel) and controls (mouse Fkbp5; lower grey panel). Arrowheads highlighting viral Fkbp5 OE in Sf1 positive neurons. C Qualitative and quantitative (D) ISH analysis confirmed successful viral Fkbp5 OE with a ∼1.6fold increase of Fkbp5 expression in Sf1^{Fkbp5 OE} animals (n = 2) compared to controls (n = 2). ESf1^{Fkbp5 OE} mice displayed a higher HFD-induced BW gain over time compared to controls. F Higher BW was reflected in a significant increase in the ratio of fat to lean mass in Sf1^{Fkbp5 OE} after 6 weeks on a HFD. G Blood glucose levels in the GTT and ITT were unaltered under a chow diet but after 9 weeks on a HFD KO animals displayed significantly increased blood glucose levels in the GTT and a trend towards increased levels in the ITT (H). Data are received from mice between 16 and 20 weeks of age and are presented as mean ± SEM. ∗p < 0.05, T < 0.1. AUC area under the curve, GTT glucose tolerance test, ITT insulin tolerance test.