Functional Effects of Schizophrenia-Associated MAP2 Phosphorylation Events

Microtubules (MTs) support myriad aspects of neuromorphological development, which is thought to be altered in schizophrenia (SZ). Microtubule-associated protein 2 (MAP2) is a prominent regulator of neuronal MT assembly and organization. Diminished immunoreactivity (IR) of this protein has been repeatedly described in post-mortem brain tissue from individuals with SZ, and recent evidence has further established that its phosphorylation state is altered in disorder, with consequence for protein function. This dissertation describes a collection of studies intended to further illuminate the scope of SZ-associated MAP2 pathology and its potential downstream consequences. Chapter 2 details an immunohistochemical experiment using postmortem brain tissue from a matched cohort of SZ and non-psychiatric comparison subjects (N = 20 pairs), examining MAP2-IR in multiple cortical regions distributed across the rostral-caudal axis. This experiment reveals that MAP2-IR deficits are conserved across cortex within-subject, bearing implications for future study and treatment of MAP2 pathology. Chapter 3, using phosphomimetic MAP2C constructs, demonstrates that a subset of SZ-associated MAP2 phosphorylation events can influence MT- and actin-binding affinity as well as MT assembly kinetics in a domain-specific manner; mutants of the proline-rich domain show suppressed MT assembly and actin-binding while maintaining MT-binding, while C-terminal domain mutants additionally have reduced MT-binding capacity. Further, the C-terminal domain mutant S426E- but not the proline-rich domain mutant T293E- has a reduced capacity for process formation upon overexpression in heterologous cells relative to wild-type protein. Finally, Chapter 4 examines the effects of phosphomimetic MAP2B mutations on MT organization/stability in heterologous HEK293T cells as well as dendritic morphology of cultured cortical neurons. I find that C-terminal domain mutants S1782E and S1799D surprisingly confer increased resistance to katanin-mediated MT severing, while the proline-rich domain mutant T1649E augments basilar dendritic arborization in mature neurons. Together, these findings indicate that SZ-associated MAP2 dysregulation is a global phenomenon within-subject, and that phosphorylation of SZ-associated sites in the proline-rich or C-terminal domains of MAP2 differentially regulate its function, with distinct consequences for cellular morphogenesis.