Differences between astrocytes and fibroblasts in the effects of TGFβ on fibronectin matrix assembly.

Fibrillar fibronectin (FN) matrix is the predominant extracellular matrix (ECM) in most tissues but in neural tissues it is limited to sites of tissue damage and disease. We investigated ECM assembly by neural cells and here we show that primary cortical astrocytes produce FN and assemble it into fibrils through a process similar to fibroblasts. Assembly is enhanced by a FN or laminin-rich substrate, but not other substrates, indicating requirement for a supportive microenvironment. FN matrix assembly was significantly increased when cells were provided with excess FN, as would happen with blood leakage into brain. Comparison of RNA-sequencing profiles of astrocytes with human and rat fibroblasts identified 63 core matrisome genes in common, including Fn1, and another 28 and 34 core matrisome genes uniquely expressed by fibroblasts and astrocytes, respectively. When fibroblasts were stimulated with TGFβ, we found 19 core matrisome genes significantly increased in both human and rat fibroblasts, including 10 genes that encode FN-binding proteins. Astrocytes up-regulate only one gene in common with fibroblasts (Tnc) of the 6 core matrisome genes that were increased by TGFβ. Surprisingly, FN expression and assembly by astrocytes were not altered by TGFβ but tenascin-C incorporation into their FN matrix was increased. Apparently the availability of an exogenous supply of plasma FN has a greater role in determining astrocyte FN matrix levels than stimulation by TGFβ. Together, our analyses show similarities in the core matrisomes of astrocytes and fibroblasts, but differences in their abilities to up-regulate core matrisome genes in response to TGFβ.