Triad3A-Mediated K48-Linked ubiquitination and degradation of TLR9 impairs mitochondrial bioenergetics and exacerbates diabetic cardiomyopathy.

Triad3A elevation induced by STZ or HG stimulation leads to degradation of TLR9 K48-linked proteasomal ubiquitination, which impairs mitochondrial function and reduces the AMP/ATP ratio and inhibits the activation of AMPK and PGC-1, which in turn leads to oxidative stress, apoptosis and fibrosis and other pathological changes. STZ: Streptozotocin; HG: High glucose; TLR9: Toll-like receptor 9; AMP: Adenosine monophosphate; ATP: Adenosine triphosphate; AMPK: Adenosine 5'-monophosphate (AMP)-activated protein kinase; PGC-1α: Peroxisome-proliferator-activated receptorγcoactivator-1α. [Display omitted] • Cardiac-specific TLR9 overexpression in diabetic mice relieved cardiac dysfunction, and remodeling. • TLR9 modulated energy metabolism in diabetes heart, but not canonical inflammatory signaling. • Triad3A can interact with TLR9 and promote its proteasomal degradation by catalyzing K48-linked ubiquitination. • PGC-1 and AMPK mediated TLR9's defense against diabetic cardiac damage and dysfunction. Targeted protein degradation represents a promising therapeutic approach, while diabetic cardiomyopathy (DCM) arises as a consequence of aberrant insulin secretion and impaired glucose and lipid metabolism in the heart.. Considering that the Toll-like receptor 9 (TLR9) signaling pathway plays a pivotal role in regulating energy metabolism, safeguarding cardiomyocytes, and influencing glucose uptake, the primary objective of this study was to investigate the impact of TLR9 on diabetic cardiomyopathy (DCM) and elucidate its underlying mechanism. Mouse model of DCM was established using intraperitoneal injection of STZ, and mice were transfected with adeno-associated virus serotype 9-TLR9 (AAV9-TLR9) to assess the role of TLR9 in DCM. To explore the mechanism of TLR9 in regulating DCM disease progression, we conducted interactome analysis and employed multiple molecular approaches. Our study revealed a significant correlation between TLR9 expression and mouse DCM. TLR9 overexpression markedly mitigated cardiac dysfunction, myocardial fibrosis, oxidative stress, and apoptosis in DCM, while inflammation levels remained relatively unaffected. Mechanistically, TLR9 overexpression positively modulated mitochondrial bioenergetics and activated the AMPK-PGC1a signaling pathway. Furthermore, we identified Triad3A as an interacting protein that facilitated TLR9′s proteasomal degradation through K48-linked ubiquitination. Inhibiting Triad3A expression improved cardiac function and pathological changes in DCM by enhancing TLR9 activity. The findings of this study highlight the critical role of TLR9 in maintaining cardiac function and mitigating pathological alterations in diabetic cardiomyopathy. Triad3A-mediated regulation of TLR9 expression and function has significant implications for understanding the pathogenesis of DCM. Targeting TLR9 and its interactions with Triad3A may hold promise for the development of novel therapeutic strategies for diabetic cardiomyopathy. Further research is warranted to fully explore the therapeutic potential of TLR9 modulation in the context of cardiovascular diseases. [ABSTRACT FROM AUTHOR]