SPARC regulates collagen interaction with cardiac fibroblast cell surfaces

Abstract

Harris BS, Zhang Y, Card L, Rivera LB, Brekken RA, Bradshaw AD. SPARC regulates collagen interaction with cardiac fibroblast cell surfaces. Am J Physiol Heart Circ Physiol 301: H841-H847, 2011. First published June 10, 2011; doi:10.1152/ajpheart.01247.2010.-Cardiac tissue from mice that do not express secreted protein acidic and rich in cysteine (SPARC) have reduced amounts of insoluble collagen content at baseline and in response to pressure overload hypertrophy compared with wild-type (WT) mice. However, the cellular mechanism by which SPARC affects myocardial collagen is not clearly defined. Although expression of SPARC by cardiac myocytes has been detected in vitro, immunohistochemistry of hearts demonstrated SPARC staining primarily associated with interstitial fibroblastic cells. Primary cardiac fibroblasts isolated from SPARC-null and WT mice were assayed for collagen I synthesis by [ 3 H]proline incorporation into procollagen and by immunoblot analysis of procollagen processing. Bacterial collagenase was used to discern intracellular from extracellular forms of collagen I. Increased amounts of collagen I were found associated with SPARC-null versus WT cells, and the proportion of total collagen I detected on SPARC-null fibroblasts without propeptides [collagen-␣ 1(I)] was higher than in WT cells. In addition, the amount of total collagen sensitive to collagenase digestion (extracellular) was greater in SPARC-null cells than in WT cells, indicating an increase in cell surface-associated collagen in the absence of SPARC. Furthermore, higher levels of collagen type V, a fibrillar collagen implicated in collagen fibril initiation, were found in SPARC-null fibroblasts. The absence of SPARC did not result in significant differences in proliferation or in decreased production of procollagen I by cardiac fibroblasts. We conclude that SPARC regulates collagen in the heart by modulating procollagen processing and interactions with fibroblast cell surfaces. These results are consistent with decreased levels of interstitial collagen in the hearts of SPARC-null mice being due primarily to inefficient collagen deposition into the extracellular matrix rather than to differences in collagen production. extracellular matrix; fibrosis; matricellular; osteonectin; secreted protein acidic and rich in cysteine THE COLLAGEN CONTENT of the cardiac interstitium is tightly regulated to preserve the form and function of the heart. Collagen in the healthy heart aligns myocytes and provides structural support; however, increased collagen deposition in response to myocardial infarction or in some types of cardiac hypertrophy can impair heart function (2, 18, 31). For example, an increase in collagen concentration is associated with chronic pressure overload, such as that seen in individuals with arterial hypertension, and is frequently associated with impaired diastolic function (14). The increase in cardiac collagen has been shown to be a significant contributor to greater diastolic stiffness (31). Increases in interstitial fibrill...

Effects of the absence of procollagen C-endopeptidase enhancer-2 on myocardial collagen accumulation in chronic pressure overload

“…For in vitro studies, 12 WT and 12 PCOLCE2-null mice were used to generate three independent primary cardiac fibroblast cultures. Fibroblasts were isolated as previously described (10). Protein isolated from detergent (1% deoxycholate) extractions of cell layers grown for 2 days in the presence of ascorbate were separated by SDS-PAGE and transferred to nitrocellulose.…”

Extracellular matrix networks in bone remodeling

“…Type III collagen mice are embryonic lethal, but analysis of null cells in culture or heterozygous mice suggests that type III collagen promotes differentiation (Volk et al, 2014). The matricellular proteins SPARC (osteonectin) and thrombospondin-2 (Alford et al, 2013) have been implicated in collagen fiber assembly (Alford et al, 2013;Bornstein, 2000;Harris et al, 2011;Rentz et al, 2007;Bradshaw et al, 2003), and also modulate osteoblast lineage progression (Hankenson and Bornstein, 2002;Hankenson et al, 2000;Alford et al, 2009;Delany et al, 2003Delany et al, , 2000. Since collagen-dependent signaling induces osteoblast differentiation, one possibility is that the effects of ECM protein deficiency in these matricellular knock-out mouse models may be explained, in part, by impaired collagen-mediated signaling.…”

Asbestos-associated mesothelial cell autoantibodies promote collagen depositionin vitro

“…We examined the potential contribution of such proteinases to MCAA-associated fibrosis. The matricellular glycoprotein SPARC (secreted protein acidic and rich in cysteine) is expressed during development and tissue remodeling and repair (Sage et al, 1989a,b) and mediates pro-collagen processing and assembly into fibrils (Harris et al, 2011; Rentz et al, 2007). Additionally, SPARC has been implicated in collagen protein expression and accumulation in bleomycin-induced pulmonary fibrosis (Strandjord et al, 1999; Wang et al, 2010) and following asbestos exposure (Pershouse et al, 2009; Wang et al, 2010).…”