TTC26 scaffolds MINDY3-mediated RACK1 deubiquitination to drive osteoclastogenesis and pathological bone resorption

Osteoclast overactivation is a central driver of bone metabolic disorders such as osteoporosis, and novel drug targets for these diseases continue to be actively explored. Scaffold proteins, which enhance the specificity of deubiquitinase (DUB)-substrate interactions, have emerged as promising therapeutic targets for the sustained management of chronic diseases. Intraflagellar transport (IFT) proteins, recognized for their scaffolding roles in cellular signaling, are increasingly implicated in bone remodeling. However, their therapeutic potential for bone metabolic disorders remains to be fully elucidated.

We systematically investigated the function of the core IFT protein, tetratricopeptide repeat protein 26 (TTC26), in osteoclastogenesis through clinical correlation analysis and mouse models (Ttc26 ^flox/flox , Lysm-Cre). Furthermore, through an integrated approach combining RNA sequencing, Western blotting, co-immunoprecipitation, in vitro osteoclast differentiation assays, and protein structural analysis, we elucidated the mechanistic role of TTC26 in regulating osteoclast differentiation. Ultimately, by osteoclast-targeted inhibition of Ttc26 (shTtc26) in ovariectomized (OVX) mice, we validated its therapeutic potential as a novel target for osteoporosis intervention.

We identified TTC26 as a previously unrecognized regulator of osteoclast differentiation. Acting as a scaffold protein, TTC26 recruits the DUB ubiquitin carboxyl-terminal hydrolase-3 (MINDY3) to promote K48-linked deubiquitination of receptor for activated kinase C-1 (RACK1), thereby stabilizing RACK1 and activating nuclear factor of activated T cells 1 (NFATc1), the master transcription factor of osteoclastogenesis. Furthermore, structural analysis reveals that six critical TTC26 residues (N533, T534, E537, R541, K545, and K548) are essential for this scaffold activity. Notably, osteoclast-targeted inhibition of Ttc26 successfully alleviates trabecular bone loss in ovariectomized (OVX) mice.

Our findings uncover a novel role for TTC26 in bone homeostasis and elucidate its molecular mechanism in driving osteoclastogenesis by scaffolding MINDY3-mediated deubiquitination of RACK1.

This study holds clear clinical translational prospects: 1) TTC26 may serve as a novel biomarker for osteoporosis diagnosis; 2) Its functional residues provide precise targets for developing small-molecule inhibitors; 3) The scaffold protein regulatory paradigm offers a new model that can be referenced for treating other bone metabolic diseases.