Trim21 Alleviates Renal Tubulointerstitial Fibrosis by Mediating Loxl2 Ubiquitination Modification and Degradation

Background: Extracellular matrix (ECM) accumulation is closely associated with renal interstitial fibrosis. However, its mechanisms is largely unknown．Tripartite motif 21 (Trim21), as a member of the TRIM family, has been demonstrated to be an E3 ubiquitin ligase. The involvement of Trim21 in immunity, inflammation, antiviral response and tumorigenesis has been documented. However, whether Trim21 involved the occurrence and development of renal interstitial fibrosis is unclear. This study aimed to investigate the role and mechanism of Trim21 in renal tubulointerstitial fibrosis. Methods: Renal tubule-specific knockout Trim21 mice were constructed, and unilateral ureteral obstruction (UUO) and ischemic reperfusion injury (IRI) were conducted to induce renal interstitial fibrosis. In vitro Trim21 overexpression plasmid or siRNA were used to disrupt Trim21 expression in cultured primary renal tubular epithelial cells, and then treated with transforming growth factor β1 (TGFβ1) for induce ECM production. Results: We first found that Trim21 mRNA and protein levels were elevated in kidney of CKD patients and UUO and IRI-induced renal interstitial fibrosis model. Moreover, knockout of Trim21 in tubular cell significantly exacerbated renal interstitial fibrosis induced by UUO and IRI. In primary renal tubular epithelial cells, silencing Trim21 upregulated lysyl oxidase-like protein 2 (Loxl2) and extracellular matrix deposition by inhibiting ubiquitination modification and degradation of Loxl2, while overexpression was the opposite. Immunoprecipitation experiments showed that PRY/SPRY domain of Trim21 interacted with amino-terminal of Loxl2. Conclusion: In summary, Trim21 directly interacts with Loxl2 through the PRY/SPRY domain, promotes ubiquitination modification and degradation of Loxl2, inhibits extracellular matrix production and attenuates renal fibrosis. Therefore, Trim21 plays an essential role in Loxl2 regulated ECM deposition and may be a viable target for treating chronic kidney diseases. Funding: Government Support – Non-U.S.