CTSK and type 1 diabetes mellitus: Although the function of osteoclasts in T1D is controversial, the present study provided evidence to support the hyperactivity of osteoclasts in T1D, as shown by increased TRAP activity (Fig. 1), larger SZ formation (Fig. 3h, i), upregulated expression of CTSK and RANKL, and downregulated expression of OPG after HG treatment (Fig. 3e).