Collaborative Regulation of LRG1 by TGF-β1 and PPAR-β/δ Modulates Chronic Pressure Overload–Induced Cardiac Fibrosis

Abstract

Background: Despite its established significance in fibrotic cardiac remodeling, clinical benefits of global inhibition of TGF (transforming growth factor)-β1 signaling remain controversial. LRG1 (leucine-rich-α2 glycoprotein 1) is known to regulate endothelial TGFβ signaling. This study evaluated the role of LRG1 in cardiac fibrosis and its transcriptional regulatory network in cardiac fibroblasts. Methods: Pressure overload–induced heart failure was established by transverse aortic constriction. Western blot, quantitative reverse transcription polymerase chain reaction, immunofluorescence, and immunohistochemistry were used to evaluate the expression level and pattern of interested targets or pathology during fibrotic cardiac remodeling. Cardiac function was assessed by pressure-volume loop analysis. Results: LRG1 expression was significantly suppressed in left ventricle of mice with transverse aortic constriction–induced fibrotic cardiac remodeling (mean difference, −0.00085 [95% CI, −0.0013 to −0.00043]; P =0.005) and of patients with end-stage ischemic-dilated cardiomyopathy (mean difference, 0.13 [95% CI, 0.012–0.25]; P =0.032). More profound cardiac fibrosis (mean difference, −0.014% [95% CI, −0.029% to −0.00012%]; P =0.048 for interstitial fibrosis; mean difference, −1.3 [95% CI, −2.5 to −0.2]; P =0.016 for perivascular fibrosis), worse cardiac dysfunction (mean difference, −2.5 ms [95% CI, −4.5 to −0.4 ms]; P =0.016 for Tau-g; mean difference, 13% [95% CI, 2%–24%]; P =0.016 for ejection fraction), and hyperactive TGFβ signaling in transverse aortic constriction–operated Lrg1 -deficient mice (mean difference, −0.27 [95% CI, −0.47 to −0.07]; P <0.001), which could be reversed by cardiac-specific Lrg1 delivery mediated by adeno-associated virus 9. Mechanistically, LRG1 inhibits cardiac fibroblast activation by competing with TGFβ1 for receptor binding, while PPAR (peroxisome proliferator-activated receptor)-β/δ and TGFβ1 collaboratively regulate LRG1 expression via SMRT (silencing mediator for retinoid and thyroid hormone receptor). We further demonstrated functional interactions between LRG1 and PPARβ/δ in cardiac fibroblast activation. Conclusions: Our results established a highly complex molecular network involving LRG1, TGFβ1, PPARβ/δ, and SMRT in regulating cardiac fibroblast activation and cardiac fibrosis. Targeting LRG1 or PPARβ/δ represents a promising strategy to control pathological cardiac remodeling in response to chronic pressure overload.

A Multifunctional Role of Leucine-Rich α-2-Glycoprotein 1 in Cutaneous Wound Healing Under Normal and Diabetic Conditions

“…Akt is essential for NOX-independent NETosis ( 33 ). Furthermore, we demonstrated that LRG1-mediated NET formation is dependent on activation of the Akt pathway through TGFβ type I receptor ALK5, which is in agreement with LRG1-mediated TGFβ signaling in ECs ( 11 ), fibroblasts ( 34 ), glioma cells ( 46 ), and T-helper 17 cells ( 47 ). We further demonstrated that Lrg1 −/− mice are resistant to diabetes-induced delay in wound closure, especially during the inflammatory phase, which is likely due to its role in NETosis.…”

“…7 G ). LRG1 was previously reported to signal through TGFβ type I receptor activin-like kinase 5 (ALK5) in non-ECs ( 34 ). For elucidation of whether LRG1-induced NETosis and Akt activation are dependent on ALK5, ALK5 was inhibited by SB431542, resulting in a complete abrogation of LRG1-induced phosphorylation of Akt and H3Cit ( Fig.…”

MicroRNA‐497 elevation or LRG1 knockdown promotes osteoblast proliferation and collagen synthesis in osteoporosis via TGF‐β1/Smads signalling pathway

“…A previous study states that the reduced expression of LRG1 is connected to the increased TGF‐β1 activity during the cardiac remodelling process in response to injury 23 . Moreover, LRG1 deletion can lead to excessive activation of TGF‐β signalling pathway, leading to increased expression of TGF‐β1 and p‐Smad2/3 24 . A strong relationship between miR‐497 and Smad7 has been recorded in the literature that the expression of miR‐497 was inversely correlated with the Smad7 expression in breast cancer tissues and oral squamous cell carcinoma 25,26 …”

“…A previous study states that the reduced expression of LRG1 is connected to the increased TGF-β1 activity during the cardiac remodelling process in response to injury 23. Moreover, LRG1 deletion can lead to excessive activation of TGF-β signalling pathway, leading to increased expression of TGF-β1 and p-Smad2/3 24. A strong relationship between miR-497…”

PPARs and Tumor Microenvironment: The Emerging Roles of the Metabolic Master Regulators in Tumor Stromal–Epithelial Crosstalk and Carcinogenesis

“…This observation suggests a pro-tumorigenic role of LRG1. Surprisingly, the LRG1 promoter has two putative PPAR response elements [ 91 ]. The expression of LRG1 is increased by a PPARβ/δ agonist, GW501516, which strongly suggests that LRG1 is a direct target of PPARβ/δ [ 91 ].…”