Raloxifene reduces sex- and age-related intervertebral disc degeneration in mice by estrogen signaling

Estrogen agonist raloxifene is an FDA-approved treatment for osteoporosis in postmenopausal women that may also be a promising prophylactic for painful intervertebral disc (IVD) degeneration. Here, we hypothesized that raloxifene would augment IVD structure and reduce neurokinin-1 (substance P) in young and old mice by stimulating estrogen signaling. 2.5 month (male and female) and 22.5 month (female) C57Bl/6J mice were subcutaneously injected with raloxifene hydrochloride (5x/week, 6week, n=7-9/grp). Next, to determine the impact of estrogen-deficiency to IVD structure and substance P, female mice were ovariectomized (OVX) at 4mo and tissues from OVX and sham-operated mice were harvested at 6mo (n=5-6/grp). First, compared to male IVD, female IVD expressed less col2 and osterix transcription, early markers of IVD degeneration. Irrespective of sex, raloxifene increased the transcriptional expression for extracellular matrix anabolism, proliferation, notochordal cells (vs chondrocyte-like cells) and estrogen signaling in young IVD. Next, we determined that biological sex and aging each induced structural features of lumbar IVD degeneration. Therapeutically, injection of raloxifene countered these features by increasing IVD height in young mice, preventing mild sex-related IVD degeneration in young female mice and partially reversing age-related IVD degeneration in old female mice. Further, estrogen agonist raloxifene upregulated er-α protein and downregulated substance P protein in young and old IVD. By contrast, estrogen-deficiency by OVX increased IVD degeneration and substance P protein in IVD cells. Similarly, substance P protein in vertebral osteocytes was upregulated in females relative to males and by estrogen-deficiency and downregulated by raloxifene. Overall, raloxifene augmented IVD structure and reduced substance P expression in young and old female murine IVD, whereas estrogen-deficiency increased substance P in the spine. These data suggest that raloxifene may potentially relieve painful IVD degeneration in postmenopausal women induced by biological sex, estrogen-deficiency and advanced age. ![Figure][1] Graphical Abstract Injection of raloxifene promotes IVD health by engaging estrogen and Wnt signaling to promote cell proliferation and IVD structure. Differential estrogen signaling by raloxifene and ovariectomy regulated nerve signaling protein substance P in the spine. Raloxifene may also bind water to collagen to promote hydration. Acan: aggrecan, AF: annulus fibrosus, NC: notochordal cell, NP: nucleus pulposus ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes