Estrogen modulates adiposity and protects against obesity-associated inflammation, oxidative stress, and insulin resistance

Abstract

Obesity is associated with numerous co-morbidities, such as chronic low-grade inflammation, oxidative stress, insulin resistance, cardiovascular disease, and some cancers. However, the role of estrogen in the susceptibility to obesity and its co-morbidities is not clear. To determine the role of estrogen in the above morbidities, we used C57BL/6J mice (15/group): 1)males 2)nonovariectomized females (novx) 3)ovariectomized females (ovx) and 4) ovariectomized females supplemented with estrogen (ovx-E), which were randomized to receive a 30% calorie-restricted, low-fat or high-fat diet. Our results showed that male and ovx-female mice were more susceptible to obesity compared to novx-female and ovx-female+E mice. Specifically, we observed that estrogen protected novx-female and ovx-female+E mice from adiposity and glucose intolerance by decreasing adipocyte size and key adipogenic and lipogenic mRNA expression levels. Further experimentation established that estrogen decreased abdominal adiposity by decreasing the number of large adipocytes. Our findings implied that estrogen stimulated lipolysis in novx-female and ovx-female+E mice. Additionally, the enlarged adipocytes observed in the male and ovx-female mice were accompanied with crown-like structures surrounding necrotic adipocytes and F480+ macrophages and elevated mRNA expression levels of CD68, IL6, and TNF[alpha]. Lastly, male and ovx-female mice exhibited liver steatosis, elevated serum ALT levels, and increased insulin resistance. To determine if there were sex differences in oxidative stress, we showed that estrogen protected the novx-female and ovx-female+E mice from adipose tissue oxidative stress as evidenced by fewer γH2AX stained nuclei and lower iNOS, P47x, GP90x, but higher catalase mRNA levels. In order to further understand the role of estrogen in adipocyte inflammation, we differentiated 3t3L1 pre-adipocytes in charcoal-stripped FBS +/- 1nM estrogen. Our findings mimicked our in vivo results; the presence of estrogen significantly decreased adipogenesis and down regulated IL6, TNF[alpha], and GP90x in 3t3L1 adipocytes. Additionally, using 4-hydroxytamoxifen, we demonstrated that the protective effects of estrogen on IL6 and TNF[alpha] mRNA expression were blocked; suggesting that estrogen could mediate its anti-inflammatory effects through ERα. In conclusion, this dissertation demonstrates that estrogen protects female mice from obesity-associated inflammation, oxidative stress, and insulin resistance by altering adipocyte morphology possibly through ER[alpha].