<p>The osteogenic capability of periodontal ligament cells in periodontitis is impaired partly due to decreased RUNX2 expression. Mass spectrometry identified TRIM21 as a protein that interacts with RUNX2 and facilitates its degradation. Pharmacological inhibition experiments revealed that blocking the lysosomal pathway significantly attenuated TRIM21-mediated RUNX2 degradation, whereas inhibition of the proteasome or macroautophagy had no such effect. Subsequent analysis revealed that the KFERQ-like motif in TRIM21 is crucial for its identification in chaperone-mediated autophagy (CMA). TRIM21 mutants lacking this motif failed to bind the chaperone protein HSC70 and could not mediate RUNX2 degradation. HSC70 identifies the KFERQ motif in TRIM21, aiding the transport of the TRIM21-RUNX2 complex to lysosomal-associated membrane protein 2A (LAMP2A) on the lysosome surface, which promotes RUNX2 degradation. In conclusion, our study demonstrated that TRIM21 mediated RUNX2 degradation through the lysosome-mediated CMA, driven by its interaction with HSC70 via the KFERQ motif. This mechanism is exacerbated in periodontitis due to elevated TRIM21 expression, leading to reduced RUNX2 levels. These findings provide new insights into the impaired osteogenic capacity in periodontitis and highlight TRIM21 as a potential therapeutic target to restore RUNX2 function and enhance bone regeneration in periodontal disease.</p> Graphical Abstract <p>1. The elevated expression of TRIM21 observed in periodontitis is related to the declined RUNX2 protein expression.</p> <p>2. TRIM21 binds to the RUNX2 in the cytoplasm and is then recognized by HSC70 via TRIM21's KFERQ motif.</p> <p>3. HSC70 transports the TRIM21-RUNX2 complex to LAMP2A in the lysosome surface, facilitating the subsequent degradation via the CMA pathway.</p> <p></p>