Appearance of tissue transglutaminase in astrocytes in multiple sclerosis lesions: a role in cell adhesion and migration?

Multiple Sclerosis (MS) is a neuroinflammatory disease mainly affecting young adults. A major pathological hallmark of MS is the presence of demyelinated lesions in the central nervous system. In the active phase of the disease, astrocytes become activated, migrate and contribute to local tissue remodeling that ultimately can result in an astroglial scar. This process is facilitated by extracellular matrix proteins, including fibronectin. Tissue Transglutaminase (TG2) is a multifunctional enzyme with a ubiquitous tissue distribution and it has been shown that inflammatory cytokines can induce TG2 activity. In addition, TG2 is known to mediate cell adhesion and migration. We therefore hypothesized that TG2 is present in MS lesions and plays a role in cell adhesion and/or migration. Our studies showed that TG2 immunoreactivity appeared in astrocytes in active and chronic active MS lesions. These TG2 positive astrocytes partly co-localized with fibronectin. Additional in vitro studies showed that TG2 mediated astrocytoma adhesion to and migration on the extracellular matrix protein fibronectin. We therefore speculate that TG2 mediates the enhanced interaction of astrocytes with fibronectin in the extracellular matrix of MS lesions, thereby contributing to astrocyte adhesion and migration, and thus in tissue remodeling and possibly glial scarring.