Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, Western University, London, ON, N6A 5C1, Canada.
Western Bone and Joint Institute, Western University, London, ON, N6A 5C1, Canada.
J Mol Med (Berl). 2021 Jun;99(6):831-844. doi: 10.1007/s00109-021-02049-3. Epub 2021 Feb 20.
Glycogen synthase kinase (GSK) 3 acts to negatively regulate multiple signaling pathways, including canonical Wnt signaling. The two mammalian GSK3 proteins (alpha and beta) are at least partially redundant. While Gsk3a KO mice are viable and display a metabolic phenotype, abnormal neuronal development, and accelerated aging, Gsk3b KO animals die late in embryogenesis or at birth. Selective Gsk3b KO in bone delays development of some bones, whereas cartilage-specific Gsk3b KO mice are normal except for elevated levels of GSK3A protein. However, the collective role of these two GSK3 proteins in cartilage was not evaluated. To address this, we generated tamoxifen-inducible, cartilage-specific Gsk3a/Gsk3b KO (described as "cDKO") in juvenile mice and investigated their skeletal phenotypes. We found that cartilage-specific Gsk3a/Gsk3b deletion in young, skeletally immature mice causes precocious growth plate (GP) remodeling, culminating in shorter long bones and hence, growth retardation. These mice exhibit inefficient breathing patterns at later stages and fail to survive. The disrupted GP in cDKO mice showed progressive loss of cellular and proteoglycan components, and immunostaining for SOX9, while BGLAP (osteocalcin) and COL2A1 increased. In addition, we observed increased osteoclast recruitment and cell apoptosis. Surprisingly, changes in articular cartilage of cDKO mice were mild compared with the GP, signifying differential regulation of articular cartilage vs GP tissues. Taken together, these findings emphasize a crucial role of two GSK3 proteins in skeletal development, in particular in the maintenance and function of GP. KEY MESSAGES: • Both GSK3 genes, together, are crucial regulators of growth plate remodeling. • Cartilage-specific deletion of both GSK3 genes causes skeletal growth retardation. • Deletion of both GSK3 genes decreases Sox9 levels and promotes chondrocyte apoptosis. • Cartilage-specific GSK3 deletion in juvenile mice culminates in premature lethality. • GSK3 deletion exhibits mild effects on articular cartilage compared to growth plate.
糖原合酶激酶 (GSK) 3 可负调控多种信号通路，包括经典 Wnt 信号通路。两种哺乳动物 GSK3 蛋白（α和β）至少部分冗余。虽然 Gsk3a KO 小鼠具有活力，表现出代谢表型、神经元发育异常和加速衰老，但 Gsk3b KO 动物在胚胎晚期或出生时死亡。骨组织中选择性 Gsk3b KO 会延迟一些骨骼的发育，而软骨特异性 Gsk3b KO 小鼠除 GSK3A 蛋白水平升高外均正常。然而，尚未评估这两种 GSK3 蛋白在软骨中的共同作用。为解决这一问题，我们在幼年小鼠中生成了可诱导型、软骨特异性 Gsk3a/Gsk3b KO（称为“cDKO”），并研究了其骨骼表型。我们发现，幼年、骨骼未成熟的小鼠中软骨特异性 Gsk3a/Gsk3b 缺失会导致生长板（GP）过早重塑，最终导致长骨变短，从而出现生长迟缓。这些小鼠在后期表现出低效的呼吸模式，无法存活。cDKO 小鼠的 GP 出现进行性细胞和蛋白聚糖成分丧失，SOX9 免疫染色减弱，而 BGLAP（骨钙素）和 COL2A1 增加。此外，我们观察到破骨细胞募集和细胞凋亡增加。出乎意料的是，与 GP 相比，cDKO 小鼠的关节软骨变化较轻微，表明关节软骨与 GP 组织的调控存在差异。综上所述，这些发现强调了两种 GSK3 蛋白在骨骼发育中的关键作用，特别是在 GP 维持和功能方面。关键信息：• 两种 GSK3 基因共同调控生长板重塑。• 软骨特异性敲除两种 GSK3 基因导致骨骼生长迟缓。• 两种 GSK3 基因缺失降低 Sox9 水平并促进软骨细胞凋亡。• 幼年小鼠中软骨特异性 GSK3 缺失最终导致早发性死亡。• 与生长板相比，GSK3 缺失对关节软骨的影响较小。
