EGFR and osteoporosis: Together with our previous reports that activation of EGFR signaling stimulates the proliferation of mesenchymal progenitors but inhibits their differentiation, and our in vivo finding that the skeleton of EGFR-deficient mice does not respond to PTH injections, we propose that EGFR signaling plays an important role in mediating the anabolic response of bone to PTH treatment and therefore, it represents a new target for anabolic osteoporosis therapy.