MAP2 is Differentially Phosphorylated in Schizophrenia, Altering its Function

Abstract

Schizophrenia (Sz) is a highly polygenic disorder, with common, rare, and structural variants each contributing only a small fraction of overall disease risk. Thus, there is a need to identify downstream points of convergence that can be targeted with therapeutics. Reduction of Microtubule-associated Protein 2 (MAP2) immunoreactivity (MAP2-IR) is present in individuals with Sz, despite no change in MAP2 protein levels. MAP2 is phosphorylated downstream of multiple receptors and kinases identified as Sz risk genes, altering its immunoreactivity and function. Using an unbiased phosphoproteomics approach we quantified 18 MAP2 phosphopeptides, 9 of which were significantly altered in Sz subjects. Network analysis grouped MAP2 phosphopeptides into 3 modules, each with a distinct relationship to dendritic spine loss, synaptic protein levels, and clinical function in Sz subjects. We then investigated the most hyperphosphorylated site in Sz, phosphoserine1782 (pS1782). Computational modeling predicted phosphorylation of S1782 reduces binding of MAP2 to microtubules, which was confirmed experimentally. We generated a transgenic mouse containing a phosphomimetic mutation at S1782 (S1782E) and found reductions in basilar dendritic length and complexity along with reduced spine density. Because only a limited number of MAP2 interacting proteins have been previously identified, we combined co-immunoprecipitation with mass spectrometry to characterize the MAP2 interactome in mouse brain. The MAP2 interactome was enriched for proteins involved in protein translation, including FMRP. These associations were shown to be functional as overexpression of wildtype and phosphomimetic MAP2 reduced protein synthesis in vitro. Finally, we found that Sz subjects with low MAP2-IR had reductions in the levels of synaptic proteins relative to nonpsychiatric control (NPC) subjects and to Sz subjects with normal and MAP2-IR, and this same pattern was recapitulated in S1782E mice. These findings suggest a new conceptual framework for Sz -that a large proportion of individuals have a "MAP2opathy" -in which hyperphosphorylation of MAP2 mediates impairments of neuronal structure, synaptic protein synthesis, and function. our subjects, finding no significant associations (all q>0.1, Table S2). Second, we surveyed MAP2 phosphopeptide abundance in a mouse model of increasing PMI. We detected 9 MAP2 phosphopeptides in this model. Fig 1b shows the detected MAP2 phosphopeptides, 8 of which demonstrate stable or linear changes over time (and thus readily accounted for by PMI matching in our subjects). The exception was peptide (RLS[+80]NVSS[+80]SGS[+80]INLLESPQLATLAEDVTAALAK) which had a nonlinear decay.We next applied Weighted Gene Co-Expression Network Analysis (WGCNA) 35 to the MAP2 phosphopeptide data from the Sz and NPC subjects. MAP2 phosphopeptides clustered into three modules (Fig 2a-c). We then used these three modules to compute eigenpeptide values for all subjects and tested these values for their associations with known pathological features...

Proteomic Analysis Unveils Expressional Changes in Cytoskeleton- and Synaptic Plasticity-Associated Proteins in Rat Brain Six Months after Withdrawal from Morphine

“…MAP2 protein was hyperphosphorylated at Thr1606, Ser1782 and Ser1784 on doubly phosphorylated phosphopeptide and hypophosphorylated at Ser1784 on triply phosphorylated phosphopeptide ( Table 2 ). The phosphosite Thr1606 is located in the proline-rich domain and its phosphorylation is known to reduce microtubule binding by MAP2 [ 79 , 80 ]. By comparing the MAP2 sequence (F1MAQ5) identified in our study with rat sequence of full-length MAP2 [ 81 ], we determined that the phosphosites Ser1782 and Ser1784 are located in the repeat 4a domain.…”

“…By comparing the MAP2 sequence (F1MAQ5) identified in our study with rat sequence of full-length MAP2 [ 81 ], we determined that the phosphosites Ser1782 and Ser1784 are located in the repeat 4a domain. Phosphorylation of Ser1782 may act to dissociate MAP2 from microtubules [ 79 ]. Tau protein was hyperphoshorylated at Ser436, Ser440, Thr648 and Ser661 ( Table 2 ).…”