The Influence of the Extracellular Matrix in Inflammation: Findings from the SPARC-Null Mouse

Matricellular proteins are secreted proteins that, among other functions, can contribute to extracellular matrix (ECM) assembly including modulation of cell:ECM interactions. Recent discoveries have indicated a fundamental role for the ECM in the regulation of inflammatory responses including cell extravasation and recruitment, immune cell differentiation, polarization, activation, and retention in tissues. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular collagen-binding protein implicated in fibrillar collagen assembly in the ECM of connective tissue as well as in basal lamina organization. Functions of SPARC in modulating cell adhesion events are also reported. Studies of phenotypic responses observed in SPARC-null mice to a variety of injury models have yielded interesting insight into the functional importance of SPARC production and aberrations in ECM structure that occur in the absence of SPARC that influence immune cell behavior and inflammatory pathways. In this review, we will discuss several examples from different tissues in which SPARC-null mice exhibited an inflammatory response distinct from those of SPARC expressing mice and provide insight into novel ECM-dependent mechanisms that influence these responses. Anat Rec, 2019. (c) 2019 Wiley Periodicals, Inc.