Involvement of Different Second Messengers in Parathyroid Hormone– and Interleukin‐1–Induced Interleukin‐6 and Interleukin‐11 Production in Human Bone Marrow Stromal Cells

Previous studies have suggested that increased secretion of bone active cytokines, such as interleukin‐6 (IL‐6) and interleukin‐11 (IL‐11), from osteoblasts and stromal cells play a pivotal role in the activation of osteoclasts and the genesis of osteoporosis. Various systemic and local factors can stimulate IL‐6/IL‐11 production, but the intracellular mechanism for such stimulation is largely unknown. In this study, we characterized the second messenger signaling in parathyroid hormone (PTH)‐ and IL‐1–induced production of IL‐6/IL‐11 and studied the possible modulating effects of estrogen. rhPTH(1–34) and rhIL‐1α dose‐dependently stimulated IL‐6 and IL‐11 production from human bone marrow stromal cells (hBMSCs). Agonists for protein kinase A (PKA) (forskolin), and protein kinase C (PKC) (phorbol 12‐myristate 13‐acetate; PMA) also stimulated IL‐6/IL‐11 production. Rp‐diastereoisomer of adenosine cyclic 3′,5′‐phosphorothioate (Rp‐cAMPS) and H‐8, inhibitors of PKA, significantly inhibited PTH‐stimulated IL‐6/IL‐11 production, but did not inhibit IL‐1–stimulated IL‐6/IL‐11 production. In contrast, staurosporine and calphostin C, inhibitors of PKC, suppressed IL‐1–stimulated, but not PTH‐stimulated, IL‐6/IL‐11 production. Pretreatment of cells with 17β‐estradiol (17β‐E 2 ) antagonized IL‐1–stimulated IL‐6 production. However, PTH‐stimulated IL‐6 production and IL‐1– and PTH‐stimulated IL‐11 production were not affected by 17β‐E 2 . Similarly, 17β‐E 2 inhibited PMA‐stimulated IL‐6 production, whereas neither forskolin‐stimulated IL‐6/IL‐11 production nor PMA‐stimulated IL‐11 production was affected by 17β‐E 2 . These results indicate that different second messengers are involved in PTH‐ and IL‐1–induced IL‐6 and IL‐11 production by hBMSCs: PTH and IL‐1 stimulate IL‐6/IL‐11 production via a PKA‐dependent and PKC‐dependent pathway, respectively. Furthermore, our results suggest that regulation of cytokine production by estrogen in hBMSCs is selective; only the IL‐1–induced IL‐6 production, which is mediated by PKC pathway, is inhibited, but PTH‐induced IL‐6 production and PTH/IL‐1–induced IL‐11 production are not inhibited by estrogen.