IL-1α, IL-1β, IL-6, and TNF-α Steady-State mRNA Levels Analyzed by Reverse Transcription-Competitive PCR in Bone Marrow of Gonadectomized Mice

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Abstract
Loss of gonadal function in both females and males is associated with increased rates of bone loss by a yet unidentified mechanism. There is ample evidence that cytokines that are produced in the bone microenvironment and stimulate the activity and/or formation of osteoclasts are involved. In the present study, we examined whether gonadectomy increases cytokine production via increased transcription in the bone marrow of mice. For this, the in vivo steady-state mRNA levels of multiple cytokines were determined in the central bone marrow compartment of mice at different time points following ovariectomy or orchidectomy by reverse transcription-competitive polymerase chain reaction. The limit of detectable differences in mRNA expression was approximately 2-fold. Bone marrow mRNA levels of the cytokines interleukin-1alpha (IL-1alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) were elevated up to 30-fold after treatment of mice with lipopolysaccharide. Following gonadectomy, there were no differences in the mRNA expression of these cytokines in bone marrow of female and male mice 4, 7, and 14 days after surgery. Gender steroid deficiency does not, therefore, increase steady-state mRNA levels of IL-1alpha, IL-1beta, IL-6, and TNF-alpha in cells of the central bone marrow compartment in mice. If changes have occurred these should have been less than 2-fold or in a small cell population. These results do not preclude an important role of these cytokines in the induction of bone loss after gonadectomy. For example, bone marrow cells situated close to the bone surface or bone cells may be responsible for increased cytokine synthesis. Alternatively, the loss of gender steroids may alter post-transcriptional events in cytokine synthesis and activity or may modify the responsiveness of target cells.