OBJECTIVE
We showed that 17β-estradiol (E
2) favors pancreatic β-cell survival via the estrogen receptor-α (ERα) in mice. E
2 activates nuclear estrogen receptors via an estrogen response element (ERE). E
2 also activates nongenomic signals via an extranuclear form of ERα and the G protein–coupled estrogen receptor (GPER). We studied the contribution of estrogen receptors to islet survival.
RESEARCH DESIGN AND METHODS
We used mice and islets deficient in estrogen receptor-α (αERKO
−/−), estrogen receptor-β (βERKO
−/−), estrogen receptor-α and estrogen receptor-β (αβERKO
−/−), and GPER (GPERKO
−/−); a mouse lacking ERα binding to the ERE; and human islets. These mice and islets were studied in combination with receptor-specific pharmacological probes.
RESULTS
We show that ERα protection of islet survival is ERE independent and that E
2 favors islet survival through extranuclear and membrane estrogen receptor signaling. We show that ERβ plays a minor cytoprotective role compared to ERα. Accordingly, βERKO
−/− mice are mildly predisposed to streptozotocin-induced islet apoptosis. However, combined elimination of ERα and ERβ in mice does not synergize to provoke islet apoptosis. In αβERKO
−/− mice and their islets, E
2 partially prevents apoptosis suggesting that an alternative pathway compensates for ERα/ERβ deficiency. We find that E
2 protection of islet survival is reproduced by a membrane-impermeant E
2 formulation and a selective GPER agonist. Accordingly, GPERKO
−/− mice are susceptible to streptozotocin-induced insulin deficiency.
CONCLUSIONS
E
2 protects β-cell survival through ERα and ERβ via ERE-independent, extra-nuclear mechanisms, as well as GPER-dependent mechanisms. The present study adds a novel dimension to estrogen biology in β-cells and identifies GPER as a target to protect islet survival.Preserving insulin secretion by the pancreatic β-cells is critical in both type 1 and the late stages of type 2 diabetes. In type 1 diabetes, the death of insulin-producing β-cells of the pancreas by apoptosis leads to insulin dependence. Insulin replacement therapy by pancreatic islet transplantation is a treatment that most closely replicates normal physiological conditions for treatment of type 1 diabetes (
1), but its effectiveness is reduced by the loss of functional islet mass from apoptosis, impairing the survival of islet grafts. Similarly, in the late stages of type 2 diabetes, evidence of β-cell apoptosis is documented in animal models (
2,
3) and in humans (
4). Thus, in the absence of novel immunotherapy and antiapoptotic drugs, novel strategies to protect insulin-producing cells in vivo represent a major opportunity for therapeutic intervention. One promising approach to protect β-cells from apoptosis involves the cytoprotective actions of estrogens. In addition to its reproductive functions, the female sex steroid 17β-estradiol (E
2) is a neuroprotective hormone against multiple oxidative and proapoptotic insults in vivo and in vitro, acting via classic estrogen receptors (rev. in
5). Recently, we reported that E
2 protects β-cells from streptozotocin (STZ)-induced apoptosis in mice of both sexes via the estrogen receptor (ER)-α (
6). In cultured mouse and human islets, E
2 has potent antiapoptotic properties against proinflammatory cytokines and reactive oxygen species (
6,
7). E
2 acts via classic estrogen receptors, ERα and ERβ (
8). In ERα-deficient female mice, E
2 still partially protects β-cell survival via an alternative pathway (
6), suggesting that ERβ may mediate the effects of E
2 in the absence of ERα.The G protein–coupled estrogen receptor (GPER), also known as GPR30, has been recognized as a membrane receptor for estrogens that mediates nongenomic signals (
9). GPER is expressed in islets and has recently been suggested to mediate the estrogenic effect on islet insulin release (
10). We analyzed the contribution of ERα, ERβ, and GPER to islet survival. We used mice individually deficient in ERα, ERβ, ERα and ERβ, and GPER; a mouse lacking ERα binding to the ERE; and human islets. These mutant mice and islets were exposed to oxidative stress using STZ or hydrogen peroxide, respectively, in combination with the use of specific pharmacological probes.
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