Complex sentence: The heavy proliferation of astrocytes also modifies the extracellular matrix surrounding the damaged region by secreting many molecules including laminin, fibronectin, tenascin C, and proteoglycans.
Split into simpler sentences: The heavy proliferation of astrocytes also modifies the extracellular matrix surrounding the damaged region by secreting many molecules. Such molecules include laminin, fibronectin, tenascin C, and proteoglycans.