Intervertebral disc degeneration is an important contributor to chronic low back and neck pain. Although many environmental and genetic factors are known to contribute to disc degeneration, age is still the most significant risk factor. Recent studies have shown that senescence may play a role in age-related disc degeneration and matrix catabolism in humans and mouse models. Clearance of p16Ink4a-positive senescent cells reduces the degenerative phenotype in many age-associated diseases. Whether p16Ink4a plays a functional role in intervertebral disc degeneration and senescence is unknown. We first characterized the senescence status of discs in young and old mice. Quantitative histology, gene expression and a novel p16tdTom reporter mice showed an increase in p16Ink4a, p21 and IL-6, with a decrease in Ki67 with aging. Accordingly, we studied the spinal-phenotype of 18-month-old mice with conditional deletion of p16Ink4a in the disc driven by Acan-CreERT2 (cKO). The analyses of discs of cKO and age-matched control mice showed little change in cell morphology and tissue architecture. The cKO mice exhibited changes in functional attributes of aggrecan as well as in collagen composition of the intervertebral disc. While cKO discs exhibited a small decrease in TUNEL positive cells, lineage tracing experiments using ZsGreen reporter indicated that the overall changes in cell fate or numbers were minimal. The cKO mice maintained expression of NP-cell phenotypic markers CA3, Krt19 and GLUT-1. Moreover, in cKO discs, levels of p19Arf and RB were higher without alterations in Ki67, γH2AX, CDK4 and Lipofuscin deposition. Interestingly, the cKO discs showed lower levels of SASP markers, IL-1β, IL-6, MCP1 and TGF-β1. These results show that while, p16Ink4a is dispensable for induction and maintenance of senescence, conditional loss of p16Ink4a reduces apoptosis, limits the SASP phenotype and alters matrix homeostasis of disc cells.

中文翻译：

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椎间盘细胞中的 p16Ink4a 缺失会影响其基质稳态和衰老相关的分泌表型，但不会改变衰老的开始。


椎间盘退变是慢性腰背和颈部疼痛的重要原因。尽管已知许多环境和遗传因素会导致椎间盘退变，但年龄仍然是最重要的危险因素。最近的研究表明，衰老可能在人类和小鼠模型中与年龄相关的椎间盘退变和基质分解代谢中发挥作用。清除 p16Ink4a 阳性衰老细胞可减少许多与年龄相关的疾病的退行性表型。 p16Ink4a 是否在椎间盘退变和衰老中发挥功能作用尚不清楚。我们首先描述了年轻和年老小鼠椎间盘的衰老状态。定量组织学、基因表达和新型 p16tdTom 报告小鼠显示，随着衰老，p16Ink4a、p21 和 IL-6 增加，而 Ki67 减少。因此，我们研究了由 Acan-CreERT2 (cKO) 驱动的椎间盘中条件性删除 p16Ink4a 的 18 个月大小鼠的脊髓表型。对 cKO 和年龄匹配的对照小鼠的椎间盘分析显示，细胞形态和组织结构几乎没有变化。 cKO 小鼠表现出聚集蛋白聚糖功能属性以及椎间盘胶原蛋白组成的变化。虽然 cKO 圆盘中 TUNEL 阳性细胞略有减少，但使用 ZsGreen 报告基因的谱系追踪实验表明，细胞命运或数量的总体变化很小。 cKO 小鼠维持 NP 细胞表型标记 CA3、Krt19 和 GLUT-1 的表达。此外，在 cKO 椎间盘中，p19Arf 和 RB 的水平较高，而 Ki67、γH2AX、CDK4 和脂褐质沉积没有改变。有趣的是，cKO 圆盘显示出较低水平的 SASP 标记物、IL-1β、IL-6、MCP1 和 TGF-β1。 这些结果表明，虽然 p16Ink4a 对于衰老的诱导和维持是可有可无的，但 p16Ink4a 的条件性缺失会减少细胞凋亡，限制 SASP 表型并改变椎间盘细胞的基质稳态。