Beta 3 Adrenergic Receptor Activation Rescues Metabolic Dysfunction in Female Estrogen Receptor Alpha-Null Mice

Metabolic disease risk escalates following menopause. The mechanism is not fully known, but likely involves reduced signaling through estrogen receptor alpha (ERα), which is highly expressed in brown and white adipose tissue (BAT and WAT).Objective: Test the hypothesis that uncoupling protein (UCP1) activation mitigates metabolic dysfunction caused by loss of signaling through ERα.Methods: At 8 weeks of age, female ERα knock out (KO) and wild-type mice were housed at 28°C and fed a Western-style high-fat, high sucrose diet (HFD) or a normal low-fat chow diet (NC) for 10 weeks. During the final 2 weeks, they received daily injections of CL 316,256 (CL), a selective β3 adrenergic agonist, or vehicle control (CTRL), creating eight groups: WT-CTRL, WT-CL, KO-CTRL, and KO-CL on HFD or NC; n = 4–10/group.Results: ERαKO demonstrated exacerbated HFD-induced adiposity gain (P < 0.001) and insulin resistance (P = 0.006). CL treatment improved insulin sensitivity (P < 0.05) and normalized ERαKO-induced adiposity increase (P < 0.05). In both genotypes, CL increased resting energy expenditure (P < 0.05) and induced WAT beiging indicated by increased UCP1 protein in both perigonadal (PGAT) and subcutaneous (SQAT) depots. These effects were attenuated under HFD conditions (P < 0.05). In KO, CL reduced HFD energy consumption compared to CTRL (P < 0.05). Remarkably, CL increased WAT ERβ protein levels of both WT and KO (P < 0.001), revealing CL-mediated changes in estrogen signaling may have protective metabolic effects.Conclusion: CL completely restored metabolic dysfunction in ERαKO mice. Thus, UCP1 may be a therapeutic target for treating metabolic dysfunction following loss of estrogen receptor signaling

Loss of Nlrp3 Does Not Protect Mice from Western Diet-Induced Adipose Tissue Inflammation and Glucose Intolerance.

We tested the hypothesis that loss of Nlrp3 would protect mice from Western diet-induced adipose tissue (AT) inflammation and associated glucose intolerance and cardiovascular complications. Five-week old C57BL6J wild-type (WT) and Nlrp3 knockout (Nlrp3-/-) mice were randomized to either a control diet (10% kcal from fat) or Western diet (45% kcal from fat and 1% cholesterol) for 24 weeks (n = 8/group). Contrary to our hypothesis that obesity-mediated white AT inflammation is Nlrp3-dependent, we found that Western diet-induced expression of AT inflammatory markers (i.e., Cd68, Cd11c, Emr1, Itgam, Lgals, Il18, Mcp1, Tnf, Ccr2, Ccl5 mRNAs, and Mac-2 protein) were not accompanied by increased caspase-1 cleavage, a hallmark feature of NLRP3 inflammasome activation. Furthermore, Nlrp3 null mice were not protected from Western diet-induced white or brown AT inflammation. Although Western diet promoted glucose intolerance in both WT and Nlrp3-/- mice, Nlrp3-/- mice were protected from Western diet-induced aortic stiffening. Additionally, Nlrp3-/- mice exhibited smaller cardiomyocytes and reduced cardiac fibrosis, independent of diet. Collectively, these findings suggest that presence of the Nlrp3 gene is not required for Western diet-induced AT inflammation and/or glucose intolerance; yet Nlrp3 appears to play a role in potentiating arterial stiffening, cardiac hypertrophy and fibrosis

Visceral white AT characterization in WT and <i>Nlrp3</i>^-/- mice fed a control diet versus Western diet.

<p>(A) Representative immunohistochemical 10X images of retroperitoneal white AT stained for Mac-2; (B) gene expression in stromal vascular cells isolated from epididymal white AT; (C) average adipocyte size in retroperitoneal white AT; (D) Mac-2 positive immunostained area in retroperitoneal white AT; (E) protein content of Mac-2 via Western blotting in retroperitoneal white AT; (F) protein content of pro-caspase-1 via Western blotting in retroperitoneal white AT; (G) protein content of p10 caspase-1 (cleavage) via Western blotting in retroperitoneal white AT; (H) representative Western blot bans. Data are expressed as means ± SE. WT, wild-type; KO, <i>Nlrp3</i> knockout, CD, control diet; WD, Western diet; D, main effect of diet; G, main effect of genotype; DxG, diet by genotype interaction. Significant p values (<0.05) are highlighted in bold. *denotes p<0.05 in panel B.</p

Animal characteristics.

<p>Animal characteristics.</p

Aortic stiffness and cardiac characterization in WT and <i>Nlrp3</i>^-/- mice fed a control diet versus Western diet.

<p>(A) Aortic pulse wave velocity; (B) representative histological cardiac 10X images stained for trichrome blue (arrows point to trichrome blue positive-stained regions); (C) cardiomyocyte diameter; (D) cardiac fibrosis (quantification of trichrome blue positive-stained area). Data are expressed as means ± SE. WT, wild-type; KO, <i>Nlrp3</i> knockout, CD, control diet; WD, Western diet; D, main effect of diet; G, main effect of genotype; DxG, diet by genotype interaction. Significant p values (<0.05) are highlighted in bold.</p

Liver characterization in WT and <i>Nlrp3</i>^-/- mice fed a control diet versus Western diet.

<p>(A) Liver weight; (B) liver triglycerides (TG); representative histological 20X images stained for H&E. Data are expressed as means ± SE. WT, wild-type; KO, <i>Nlrp3</i> knockout, CD, control diet; WD, Western diet; D, main effect of diet; G, main effect of genotype; DxG, diet by genotype interaction. Significant p values (<0.05) are highlighted in bold.</p

Glucose tolerance testing (GTT) in WT and <i>Nlrp3</i>^-/- mice fed a control diet versus Western diet at 15 and 25 weeks of age.

<p>(A) Glucose levels after glucose injection; (B) glucose area under the curve (AUC) during GTT. Data are expressed as means ± SE. WT, wild-type; KO, <i>Nlrp3</i> knockout, CD, control diet; WD, Western diet; D, main effect of diet; G, main effect of genotype; DxG, diet by genotype interaction. Significant p values (<0.05) are highlighted in bold.</p

Body weight and composition in WT and <i>Nlrp3</i>^-/- mice fed a control diet versus Western diet.

<p>(A) Weekly body weights; (B) final body weight; (C) final % body fat. Data are expressed as means ± SE. WT, wild-type; KO, <i>Nlrp3</i> knockout, CD, control diet; WD, Western diet; D, main effect of diet; G, main effect of genotype; DxG, diet by genotype interaction. Significant p values (<0.05) are highlighted in bold.</p

AT gene expression in WT and <i>Nlrp3</i>^-/- mice fed a control diet versus Western diet.

<p>(A) Visceral white (i.e., retroperitoneal) AT; (B) brown (i.e., interscapular) AT. Data are expressed as means ± SE. WT, wild-type; KO, <i>Nlrp3</i> knockout, CD, control diet; WD, Western diet; D, main effect of diet (p<0.05); G, main effect of genotype (p<0.05). No significant interactions were found.</p