Sex Hormones Attenuate Pro-Inflammatory Gene Expression in Nucleus Pulposus and Annulus Fibrosus Cells in a Cell-Type Specific Manner.

Background: Intervertebral disc (IVD) degeneration is a major contributor to back pain and disability. The cause of IVD degeneration is multifactorial, with no disease-modifying treatments. Sex steroids, primarily testosterone and its derivatives, are becoming increasingly common in the clinic for the treatment of low back pain and continue to be used as ergogenic aids in sport. While outcomes at the level of pain and athletic performance are promising, little research has investigated the effects of these hormones on the biology of the IVD and how sex hormones may directly influence joint health and homeostasis. Methods: Primary bovine nucleus pulposus (NP) and annulus fibrosus (AF) cells were isolated from 18-month-old female bovine caudal IVDs for primary cell culture. These cells were subjected to sex hormone stimulation (5α-dihydrotestosterone or 17β-estradiol) at increasing doses (0, 25, 50, 75, 100, 125 nM) with or without a pro-inflammatory stimulus (IL-1β; 10 ng/mL or TNFα; 25 ng/mL) to model healthy and pro-inflammatory environments, respectively. Cells were harvested for analysis of gene expression, cytokine secretion, and to assess NF-κB signaling. Results: In both NP and AF cells (dihydro)testosterone and 17β-estradiol decreased proinflammatory gene expression and cytokine release. Changes induced by sex hormones were cell-type dependent and specific to the inflammatory stimulus used. NP cells displayed a robust inflammatory response to IL-1β compared to TNFα, while AF cells responded to TNFα only, but only at the level of gene expression. Attenuation of inflammatory gene expression by sex hormone exposure was not associated with changes in p65 phosphorylation or NF-κB pathway associated gene expression. Conclusion: Sex hormones such as dihydrotestosterone and estrogen play an important role mediating inflammatory signaling in cells of the IVD, finding which could lead to novel therapeutics for IVD degeneration.