NMNAT2 in cortical glutamatergic neurons exerts both cell and non-cell autonomous influences to shape cortical development and to maintain neuronal health

Here we show that deleting NMNAT2 from cortical glutamatergic neurons (NMNAT2 cKO) results in progressive axonal loss, neuroinflammation, small hippocampi and enlarged ventricles. Interestingly, dramatic neuroinflammation responses were observed around the long-range axonal tracts of NMNAT2 cKO cortical neurons. In addition to the neurodegenerative-like phenotype, we also found the absence of whisker-representation patterns "barrels" in the primary somatosensory cortex of NMNAT2 cKO mice. These observations suggest that NMNAT2 is required in developing cortical circuits and in maintaining the health of cortical neurons. Unbiased transcriptomic analysis suggests that NMNAT2 loss in cortical neurons after axonal outgrowth phase upregulates mitochondria function while greatly reducing synaptogenesis pathways. Complete loss of Sarm1 function in NMNAT2 cKO mice restores barrel map formation and axonal integrity and abolishes the inflammatory response. Interestingly, reducing Sarm1 function in NMNAT2 cKO mice by deleting only one copy of Sarm1 restores barrel map formation but did not diminish the neurodegenerative-like phenotype. Only complete loss of Sarm1 prevents neurodegeneration and inflammatory responses.