Pycard deficiency inhibits microRNA maturation and prevents neointima formation by promoting chaperone-mediated autophagic degradation of AGO2/argonaute 2 in adipose tissue

by Selleckchem | Jan 06 2024

PYCARD (PYD and CARD domain containing), a pivotal adaptor protein in inflammasome assembly and activation, contributes to innate immunity, and plays an essential role in the pathogenesis of atherosclerosis and restenosis. However, its roles in microRNA biogenesis remain unknown. Therefore, this study aimed to investigate the roles of PYCARD in miRNA biogenesis and neointima formation using pycard knockout (pycard-/-) mice. Deficiency of Pycard reduced circulating miRNA profile and inhibited Mir17 seed family maturation. The systemic pycard knockout also selectively reduced the expression of AGO2 (argonaute RISC catalytic subunit 2), an important enzyme in regulating miRNA biogenesis, by promoting chaperone-mediated autophagy (CMA)-mediated degradation of AGO2, specifically in adipose tissue. Mechanistically, pycard knockout increased PRMT8 (protein arginine N-methyltransferase 8) expression in adipose tissue, which enhanced AGO2 methylation, and subsequently promoted its binding to HSPA8 (heat shock protein family A (Hsp70) member 8) that targeted AGO2 for lysosome degradation through chaperone-mediated autophagy. Finally, the reduction of AGO2 and Mir17 family expression prevented vascular injury-induced neointima formation in Pycard-deficient conditions. Overexpression of AGO2 or administration of mimic of Mir106b (a major member of the Mir17 family) prevented Pycard deficiency-mediated inhibition of neointima formation in response to vascular injury. These data demonstrate that PYCARD inhibits CMA-mediated degradation of AGO2, which promotes microRNA maturation, thereby playing a critical role in regulating neointima formation in response to vascular injury independently of inflammasome activity and suggest that modulating PYCARD expression and function may represent a powerful therapeutic strategy for neointima formation.

Comments:

This study highlights an intriguing connection between PYCARD, microRNA biogenesis, and neointima formation, shedding light on PYCARD's role beyond its known functions in inflammasome assembly and innate immunity.

The findings suggest that PYCARD deficiency affects the circulating miRNA profile by inhibiting the maturation of the Mir17 seed family. This inhibition seems to be linked to the reduction of AGO2 expression, a crucial enzyme in miRNA biogenesis. The mechanism involves PYCARD's role in preventing the chaperone-mediated autophagy (CMA)-mediated degradation of AGO2, particularly in adipose tissue.

The study suggests a cascade of events: Pycard knockout increases PRMT8 expression, which enhances AGO2 methylation. This modification leads to increased binding of AGO2 to HSPA8, marking AGO2 for lysosomal degradation through chaperone-mediated autophagy. Ultimately, this reduction in AGO2 levels results in decreased Mir17 family expression, contributing to the prevention of vascular injury-induced neointima formation in Pycard-deficient conditions.

Moreover, the study implies potential therapeutic implications. Overexpression of AGO2 or administration of a mimic of Mir106b (a significant member of the Mir17 family) can counteract the inhibition of neointima formation caused by Pycard deficiency in response to vascular injury.

This research suggests a novel role for PYCARD in modulating AGO2 levels and microRNA biogenesis, influencing vascular injury-induced neointima formation independently of its known functions in inflammasome activity and innate immunity. The findings propose PYCARD as a potential therapeutic target for conditions involving neointima formation, providing a possible avenue for future treatments.