Bhadouria Neharika, Berman Alycia G, Wallace Joseph M, Holguin Nilsson
School of Mechanical Engineering, Purdue University, West Lafayette, IN, United States.
Department of Mechanical and Energy Engineering, Indiana University-Purdue University Indianapolis, Indianapolis, IN, United States.
Front Bioeng Biotechnol. 2022 Aug 11;10:924918. doi: 10.3389/fbioe.2022.924918. eCollection 2022.
Estrogen agonist raloxifene is an FDA-approved treatment of osteoporosis in postmenopausal women, which may also be a promising prophylactic for painful intervertebral disc (IVD) degeneration. Here, we hypothesized that 1) aging and biological sex contribute to IVD degeneration by reducing estrogen signaling and that 2) raloxifene stimulates estrogen signaling to protect against age- and sex-related IVD degeneration in mice. 2.5-month-old (male and female) and 22.5-month-old (female) C57Bl/6J mice were subcutaneously injected with raloxifene hydrochloride 5x/week for 6 weeks ( = 7-9/grp). Next, female mice were ovariectomized (OVX) or sham operated at 4 months of age and tissues harvested at 6 months ( = 5-6/grp). Advanced aging and OVX increased IVD degeneration score, weakened IVD strength, reduced estrogen receptor-α (ER-α) protein expression, and increased neurotransmitter substance P (SP) expression. Similar to aging and compared with male IVDs, female IVDs were more degenerated, mechanically less viscoelastic, and expressed less ER-α protein, but unlike the effect induced by aging or OVX, IVD mechanical force was greater in females than in males. Therapeutically, systemic injection of raloxifene promoted ER-α protein to quell these dysregulations by enlarging IVD height, alleviating IVD degeneration score, increasing the strength and viscoelastic properties of the IVD, and reducing IVD cell expression of SP in young-adult and old female mice. Transcriptionally, injection of raloxifene upregulated the gene expression of and extracellular matrix-related anabolism in young-adult and old IVD. In vertebra, advanced aging and OVX reduced trabecular BV/TV, whereas injection of raloxifene increased trabecular BV/TV in young-adult and old female mice, but not in young-adult male mice. In vertebra, advanced aging, OVX, and biological sex (females > males) increased the number of SP-expressing osteocytes, whereas injection of raloxifene reduced the number of SP-expressing osteocytes in young-adult female and male mice and old female mice. Overall, injection of estrogen agonist raloxifene in mice normalized dysregulation of IVD structure, IVD mechanics, and pain-related SP expression in IVD cells and osteocytes induced by aging and biological sex. These data suggest that, in addition to bone loss, raloxifene may relieve painful IVD degeneration in postmenopausal women induced by advanced age, biological sex, and estrogen depletion.
雌激素激动剂雷洛昔芬是一种经美国食品药品监督管理局（FDA）批准用于治疗绝经后女性骨质疏松症的药物，它也可能是一种有前景的预防疼痛性椎间盘退变的药物。在此，我们提出假说：1）衰老和生物性别通过降低雌激素信号传导导致椎间盘退变；2）雷洛昔芬刺激雌激素信号传导以预防小鼠与年龄和性别相关的椎间盘退变。将2.5月龄（雄性和雌性）和22.5月龄（雌性）的C57Bl/6J小鼠每周皮下注射盐酸雷洛昔芬5次，持续6周（每组n = 7 - 9）。接下来，雌性小鼠在4月龄时进行卵巢切除术（OVX）或假手术，并在6月龄时采集组织（每组n = 5 - 6）。衰老加剧和卵巢切除增加了椎间盘退变评分，削弱了椎间盘强度，降低了雌激素受体-α（ER-α）蛋白表达，并增加了神经递质P物质（SP）的表达。与衰老情况相似，与雄性椎间盘相比，雌性椎间盘退变更严重，力学上黏弹性更低，且ER-α蛋白表达更少，但与衰老或卵巢切除所诱导的效应不同，雌性的椎间盘机械力大于雄性。在治疗方面，全身注射雷洛昔芬通过增加椎间盘高度、减轻椎间盘退变评分、提高椎间盘的强度和黏弹性特性以及降低年轻成年和老年雌性小鼠椎间盘细胞中SP的表达，促进ER-α蛋白以平息这些失调。在转录水平上，注射雷洛昔芬上调了年轻成年和老年椎间盘与细胞外基质相关的合成代谢基因的表达。在椎骨中，衰老加剧和卵巢切除降低了小梁骨体积分数（BV/TV），而注射雷洛昔芬增加了年轻成年和老年雌性小鼠的小梁骨BV/TV，但在年轻成年雄性小鼠中未增加。在椎骨中，衰老加剧、卵巢切除以及生物性别（雌性>雄性）增加了表达SP的骨细胞数量，而注射雷洛昔芬减少了年轻成年雌性和雄性小鼠以及老年雌性小鼠中表达SP的骨细胞数量。总体而言，在小鼠中注射雌激素激动剂雷洛昔芬可使衰老和生物性别所诱导的椎间盘结构、椎间盘力学以及椎间盘细胞和骨细胞中与疼痛相关的SP表达的失调恢复正常。这些数据表明，除了骨质流失外，雷洛昔芬可能缓解绝经后女性因年龄增长、生物性别和雌激素缺乏所导致的疼痛性椎间盘退变。
