|Ronis, Martin -|
Submitted to: Alcoholism: Clinical and Experimental
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2009
Publication Date: June 15, 2009
Citation: Ronis, M.J. 2009. The ERK-STAT3 signaling cascade as a target for ethanol-estradiol cross-talk in osteoblasts [abstract]. Alcoholism: Clinical and Experimental Research. 33(S1):291A. Program No. S099. Technical Abstract: The skeleton is a well-established target of ethanol (EtOH)-mediated toxicity, and alcohol consumption is a known risk factor for both bone loss and development of osteoporosis. We have previously demonstrated in a female rat model of EtOH exposure using total enteral nutrition that EtOH produces bone loss by two different mechanisms: inhibition of bone formation and stimulation of bone resorption. Which mechanism predominates is dependent on estrogenic status. In pregnant and estrogen (E2)-supplemented female rats, EtOH-associated bone loss is smaller and is associated with inhibited formation relative to cycling females where EtOH stimulates bone resorption and increased osteoclastogenesis. In EtOH-exposed cycling females increased osteoclast (OC) numbers are associated with increased expression of the TNF family member RANKL which signals through its receptor RANK on the surface of OC precursors to increase OC differentiation. This action of EtOH is replicated in co-cultures of differentiated primary osteoblasts (OBs) and OC precursors derived from bone marrow and is the result of increased RANKL expression in EtOH-exposed OBs. We have shown that EtOH-induction of RANKL is associated with increased phosphorylation of ERK and its downstream target STAT3 and translocation of ERK into the nucleus of OBs. The ERK inhibitor PD9858, the STAT3 inhibitor AG490, treatment with E2 and with the antioxidant N-acetylcysteine (NAC) all prevented EtOH induction of RANKL in OBs and both E2 and NAC inhibited ERK phosphorylation suggesting the involvement of a ROS- ERK-STAT3 cascade in EtOH induction of RANKL and cross-talk with E2 receptor-mediated pathways. Interestingly, phosphorylation of ERK and STAT3 required a minimum of 2-3 h of EtOH treatment in vitro and was sustained over a 48-h period. Moreover EtOH-induction of RANKL was inhibited by co-treatment with cycloheximide suggesting a requirement for protein synthesis. We have demonstrated induction of a novel and constitutively active member of the NADPH-oxidase family, NOX4, in EtOH-treated OBs. The NOX inhibitor DPI prevented EtOH induction of RANKL in OBs and reversed EtOH-induced bone loss in cycling female rats in vivo. These data suggest that EtOH increases bone resorption as a result of ROS production mediated via induction of NOX4 in OBs and activation of a downstream MAP kinase pathway through ERK-STAT3 and RANKL and that inhibitory cross-talk with this cascade is responsible for E2 protection against EtOH-induced bone resorption.