Implication for transglutaminase 2-mediated activation of β-catenin signaling in neointimal vascular smooth muscle cells in chronic cardiac allograft rejection

Abstract

BACKGROUND Cardiac allograft vasculopathy (CAV) remains the main cause of long-term transplant rejection. It is characterized by hyperproliferation of vascular smooth muscle cells (VSMCs). Canonical β-catenin signaling is a critical regulator of VSMC proliferation in development; however, the role of this pathway and its regulation in CAV progression are obscure. We investigated the activity of β-catenin signaling and the role for a putative activating ligand, transglutaminase 2 (TG2), in chronic cardiac rejection. METHODS Hearts from Bm12 mice were transplanted into C57BL/6 mice (Class II mismatch), and allografts were harvested 8 weeks after transplantation. Accumulation and sub-cellular distribution of β-catenin protein and expression of several components of β-catenin signaling were analyzed as hallmarks of pathway activation. In vitro, PDGF treatment was used to mimic the inflammatory milieu in VSMC and organotypic heart slice cultures. RESULTS Activation of β-catenin in allografts compared to isografts or naïve hearts was evidenced by the augmented expression of β-catenin target genes, as well as the accumulation and nuclear localization of the β-catenin protein in VSMCs of the occluded allograft vessels. Expression of TG2, an activator of β-catenin signaling in VSMCs, was dramatically increased in allografts. Further, our ex vivo data demonstrate that TG2 is required for VSMC proliferation and for β-catenin activation by PDGF in cardiac tissue. CONCLUSIONS β-catenin signaling is activated in occluded vessels in murine cardiac allografts. TG2 is implicated as an endogenous activator of this signaling pathway and may therefore have a role in the pathogenesis of CAV during chronic allograft rejection.

Transglutaminase 2 Promotes PDGF-Mediated Activation of PDGFR/Akt1 and β-Catenin Signaling in Vascular Smooth Muscle Cells and Supports Neointima Formation

“…4). In agreement with previous studies, we did not detect nuclear β-catenin in wild-type TG2+/+ VSMCs in the absence of PDGF [44, 48, 50]. PDGF treatment resulted in nuclear accumulation of β-catenin protein in the majority of TG2+/+, but only in a few TG2-/- cells (fig.…”

“…Interestingly, in vitro the accumulation of nuclear β-catenin was described as a common outcome of Wnt and growth factor signaling in VSMC proliferation [59]. However, the activation of β-catenin in the occluded cardiac vessels of rejected mouse heart allografts was not accompanied by elevated levels of canonical Wnt ligands but did associate with increased levels of TG2 [48]. Hence, in the absence of canonical Wnt ligands, TG2 may function as an unconventional activator of β-catenin signaling [48, 50] to drive the phenotypic switch of VSMCs and the hyperplastic response in the blood vessel wall and may therefore also act as an essential link between β-catenin and growth factor signaling in VSMC proliferation.…”

“…Ex vivo , neointima formation was induced by PDGF in organotypic heart slice cultures [48, 55]. Briefly, 1 mm-thick transverse sections of hearts from 3-day old wild-type TG2+/+ or TG2-/- mice, sliced with a rodent heart matrix (Harvard Apparatus), were cultured on a Millicell-CM 0.4 μm membrane (Millipore) covered with a thin layer of heart medium (Dulbecco's modified Eagle's:F12 medium supplemented with 20% knockout serum replacement, 1% nonessential amino acids, 2 mM L-glutamine, 0.1% β-mercaptoethanol, and 0.1% penicillin/streptomycin) in the presence or absence of 0.5 nM recombinant mouse PDGF-BB (ProSpec, East Brunswick, NJ).…”

Transglutaminase Inhibitors Attenuate Vascular Calcification in a Preclinical Model

“…Noteworthy, increase in MHC gene expression did not translate into a noticeable increase in protein (Supplemental Figure VC). This finding, combined with the lack of significant quercetin effects on the VSMC proliferation 37 and apoptosis (Supplemental Fig. IB), and similar arterial wall thickness (Fig.…”

Attenuation of Chondrogenic Transformation in Vascular Smooth Muscle by Dietary Quercetin in the MGP-Deficient Mouse Model

“…In adult vessels, the β-catenin pathway is usually dormant but activates in disease [35]. In particular, a critical role for β-catenin signaling has been shown in warfarin-induced calcification [36,37]. Further, Wnt/β-catenin signaling has also been implicated in BMP2-induced aortic mineralization in the diabetic LDLR-/- mice [38] and in calcification of heart valves [39].…”