Thrombospondin-1 promotes matrix homeostasis by interacting with collagen and lysyl oxidase precursors and collagen cross-linking sites

Abstract

Fibrillar collagens of the extracellular matrix are critical for tissue structure and physiology; however, excessive or abnormal deposition of collagens is a defining feature of fibrosis. Regulatory mechanisms that act on collagen fibril assembly potentially offer new targets for antifibrotic treatments. Tissue weakening, altered collagen fibril morphologies, or both, are shared phenotypes of mice lacking matricellular thrombospondins. Thrombospondin-1 (TSP1) plays an indirect role in collagen homeostasis through interactions with matrix metalloproteinases and transforming growth factor-β1 (TGF-β1). We found that TSP1 also affects collagen fibril formation directly. Compared to skin from wild-type mice, skin from mice had reduced collagen cross-linking and reduced prolysyl oxidase (proLOX) abundance with increased conversion to catalytically active LOX. In vitro, TSP1 bound to both the C-propeptide domain of collagen I and the highly conserved KGHR sequences of the collagen triple-helical domain that participate in cross-linking. TSP1 also bound to proLOX and inhibited proLOX processing by bone morphogenetic protein-1. In human dermal fibroblasts (HDFs), TSP1 and collagen I colocalized in intracellular vesicles and on extracellular collagen fibrils, whereas TSP1 and proLOX colocalized only in intracellular vesicles. Inhibition of LOX-mediated collagen cross-linking did not prevent the extracellular association between collagen and TSP1; however, treatment of HDFs with KGHR-containing, TSP1-binding, triple-helical peptides disrupted the collagen-TSP1 association, perturbed the collagen extracellular matrix, and increased myofibroblastic differentiation in a manner that depended on TGF-β receptor 1. Thus, the extracellular KGHR-dependent interaction of TSP1 with fibrillar collagens contributes to fibroblast homeostasis.

Thrombospondin 1 and Its Diverse Roles as a Regulator of Extracellular Matrix in Fibrotic Disease

“…127 , 128 New data provide interesting evidence for direct TSP1-collagen interactions in regulating collagen fibril formation. 12 In this work, Rosini et al 12 identified TSP1 binding sites in the C-propeptide domain of intracellular pools of collagen and in a KGHR containing conserved sequence in crosslinking sites in the triple helical region of mature, secreted collagen. Interestingly, both COMP and thrombospondin-4 (TSP4) were shown to bind to the GXKGHR motif in collagen type II, suggesting a conservation of this interaction with fibrillar collagens among these TSP family members.…”

“…The TSP1-KGHR interaction is important in fibroblast homeostasis as peptides that disrupt this interaction increase alpha-smooth muscle actin (α-SMA)-positive myofibroblasts in a manner dependent on signaling through TGF-β receptor I. 12 These findings are intriguing and suggest that TSP1-procollagen/ collagen interactions potentially regulate collagen trafficking, processing, and fibril assembly. These data also suggest that TSP1 bound to collagen in the ECM potentially "normalizes" collagen matrix and prevents myofibroblast differentiation, thus indicating a possible antifibrotic role for collagen-bound TSP1.…”

“…10,11 In addition, there are roles for TSP1 in regulating collagen matrix assembly and crosslinking. 5,12,13 Moreover, there is an emerging appreciation that intracellular TSP1 might have roles in endoplasmic reticulum (ER) stress and calcium regulation. 14,15 In this review, we will first focus on known roles for TSP1 in fibrotic renal diseases, with an emphasis on its role in controlling latent TGF-β activation ( Fig.…”

Why Are Viscosity and Nonlinearity Bound to Make an Impact in Clinical Elastographic Diagnosis?

“…During the synthesis of collagen there is a process of hydroxylation that determines the crosslink formation, setting the adhesion of the new fibrils [14,15]. This is a critical step in the development of pathologies related to collagen [16], such as fibrosis-associated pathologies, as shown on foreskin cell cultures [17]. When several fibrils are adhered, they increase the crosslink density, creating a stiffer fiber, 1-20 µm in diameter [18], and completing the fibrillogenesis process [19][20][21][22][23].…”

Differential cleavage of lysyl oxidase by the metalloproteinases BMP1 and ADAMTS2/14 regulates collagen binding through a tyrosine sulfate domain

“…Not only are proteolytic events responsible for the removal of the propeptides, but also one of involved proteases, namely BMP1, cleaves the LOX precursor to generate the propeptide, for which biological activities have been also reported, and the fully active LOX (7)(8)(9)(10). This simple picture is, however, challenged by experimental evidence showing that different mature forms co-exist and contribute to LOX-mediated actions (11)(12)(13)(14). The molecular mechanisms leading to this behavior, which may arise not only by alternative proteolytic processing but also because of post-translational modifications (PTM), have not been established, and its study might indeed shed fresh light on the biological function of LOX.…”