TGF-β Fibrosis Pathway Antibody Sampler Kit

Background

Transforming growth factor-β (TGF-β) superfamily members are critical regulators of cell proliferation and differentiation, developmental patterning and morphogenesis, and disease pathogenesis (1-4). In the context of fibrosis, TGF-β signaling to SMAD2/3 is one of the biggest drivers of the profibrotic program (5).

TGF-β elicits signaling through three cell surface receptors: type I (RI), type II (RII), and type III (RIII). In response to ligand binding, the type II receptors form stable heterotrimeric complexes with the type I receptors, allowing phosphorylation and activation of type I receptor kinase. Activated type I receptors associate with SMAD2/3 and phosphorylate them on a conserved carboxy terminal SSXS motif. The phosphorylated SMADs dissociate from the receptor and form a heterotrimeric complex with the co-Smad (Smad4), allowing translocation of the complex to the nucleus. Once in the nucleus, phosphorylated SMAD2/3 targets a subset of DNA binding proteins to regulate the transcriptional program (6-8).

In the context of fibrosis, SMAD2/3 activation upregulates expression of profibrotic genes such as COL1A1 and other ECM modulators that modify the extracellular matrix of the tissue. (9). TGF-β/ SMAD2/3 signaling also induces expression of α-Smooth Muscle Actin in fibroblasts, causing transformation of these cells to myofibroblasts (10). Myofibroblasts further modify the ECM, causing excessive accumulation of collagens and other ECM components. Injury to the tissue attracts macrophages and other immune cells and the fibrotic tissue soon becomes a site of inflammation (11). In this pro-fibrotic, pro-inflammatory environment, YKL-40, also known as Chitinase-3-like protein 1 (CHI3L1), is secreted. YKL-40 is a pro-inflammatory glycoprotein that also contributes to the progression of fibrosis (12). Measurement of collagen content, α-Smooth Muscle Actin, and the release of YKL-40 are predictive of fibrotic activity.