Bekki H, Duffy T, Okubo N, Olmer M, Alvarez-Garcia O, Lamia K, Kay S, Lotz M
Department of Molecular Medicine, Scripps Research, La Jolla, CA, USA.
Keck School of Medicine, University of Southern California, Los Angeles, CA, 90089, USA.
Osteoarthritis Cartilage. 2020 Jul;28(7):966-976. doi: 10.1016/j.joca.2020.04.004. Epub 2020 Apr 24.
Abnormal chondrocyte gene expression promotes osteoarthritis (OA) pathogenesis. A previous RNA-sequencing study revealed that circadian rhythm pathway and expression of core clock gene cryptochrome 2 (CRY2) are dysregulated in human OA cartilage. Here we determined expression patterns and function CRY1 and CRY2.
CRY mRNA and protein expression was analyzed in normal and OA human and mouse cartilage. Mice with deletion of Cry1 or Cry2 were analyzed for severity of experimental OA and to determine genes and pathways that are regulated by Cry.
In human OA cartilage, CRY2 but not CRY1 staining and mRNA expression was significantly decreased. Cry2 was also suppressed in mice with aging-related OA. Cry2 knock out (KO) but not Cry1 KO mice with experimental OA showed significantly increased severity of histopathological changes in cartilage, subchondral bone and synovium. In OA chondrocytes, the levels of CRY1 and CRY2 and the amplitude of circadian fluctuation were significantly lower. RNA-seq on knee articular cartilage of wild-type and Cry2 KO mice identified 53 differentially expressed genes, including known Cry2 target circadian genes Nr1d1, Nr1d2, Dbp and Tef. Pathway analysis that circadian rhythm and extracellular matrix remodeling were dysregulated in Cry2 KO mice.
These results show an active role of the circadian clock in general, and of CRY2 in particular, in maintaining extracellular matrix (ECM) homeostasis in cartilage. This cell autonomous network of circadian rhythm genes is disrupted in OA chondrocytes. Targeting CRY2 has potential to correct abnormal gene expression patterns and reduce the severity of OA.
软骨细胞基因表达异常促进骨关节炎（OA）的发病机制。先前的一项RNA测序研究表明，昼夜节律通路以及核心生物钟基因隐花色素2（CRY2）的表达在人类OA软骨中失调。在此，我们确定了CRY1和CRY2的表达模式及功能。
分析正常和OA人类及小鼠软骨中CRY mRNA和蛋白的表达。对Cry1或Cry2缺失的小鼠进行实验性OA严重程度分析，并确定受Cry调控的基因和通路。
在人类OA软骨中，CRY2而非CRY1的染色及mRNA表达显著降低。在与衰老相关的OA小鼠中，Cry2也受到抑制。实验性OA的Cry2基因敲除（KO）小鼠而非Cry1 KO小鼠，其软骨、软骨下骨和滑膜的组织病理学变化严重程度显著增加。在OA软骨细胞中，CRY1和CRY2的水平以及昼夜波动幅度显著降低。对野生型和Cry2 KO小鼠膝关节软骨进行RNA测序，鉴定出53个差异表达基因，包括已知的Cry2靶标昼夜节律基因Nr1d1、Nr1d2、Dbp和Tef。通路分析表明，Cry2 KO小鼠的昼夜节律和细胞外基质重塑失调。
这些结果表明，昼夜节律时钟，特别是CRY2，在维持软骨细胞外基质（ECM）稳态中发挥着积极作用。这种昼夜节律基因的细胞自主网络在OA软骨细胞中被破坏。靶向CRY2有可能纠正异常基因表达模式并降低OA的严重程度。
