Glycogen synthase kinase 3 alpha/beta deletion induces precocious growth plate remodeling and cell loss in mice

Abstract

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 delayed development of some bones, whereas cartilage-specific Gsk3b KO mice are normal except for elevated levels of GSK3alpha 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 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 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 growth plates in KO mice showed progressive loss of cellular and proteoglycan components and Sox9 positive cells, with increased staining for osteocalcin and type II collagen. In addition, an increase in osteoclast recruitment and cell apoptosis was observed in growth plates. Surprisingly, changes in articular cartilage of Gsk3a/Gsk3b KO mice were mild compared to growth plates, signifying differential regulation of articular cartilage vs growth plate tissues. Taken together, these findings emphasize a crucial role of two GSK3 proteins in skeletal development, in particular in the maintenance and function of growth plates. SignificanceGrowth plate cartilage dynamics determine the rate of endochondral bone growth and thus, our final height. These processes are disturbed in many genetic and acquired diseases, but the intracellular mechanisms responsible for normal growth plate function, as well as the cessation of growth plate activity in puberty, are poorly understood. Here, we demonstrate that specific removal of both GSK3 genes (Gsk3a and Gsk3b) in postnatal cartilage of mice leads to a severe reduction of endochondral bone growth, premature remodelling of the growth plate, and early death. In contrast, articular cartilage is only mildly affected by deletion of both genes. These studies identify GSK3 signaling as a key regulator of growth plate dynamics and endochondral bone growth.