INPP5D

INPP5D (commonly known as SHIP1) is a powerful lipid phosphatase that serves as the central "off-switch" for the microglial PI3K pathway. It sits exactly downstream of major microglial receptors—including TREM2 and CSF1R—where its physiological job is to convert PIP3 into PIP2, thereby terminating survival and activation signals.

GWAS meta-analyses firmly established INPP5D as a late-onset Alzheimer’s disease risk locus. Pathologically, elevated INPP5D activity is frequently found in human AD brains, particularly in microglia clustering around amyloid plaques. Because INPP5D directly depletes the PIP3 pool, it completely neutralizes the PI3K-AKT signaling that microglia desperately need to maintain phagocytosis and cell survival.

When INPP5D levels are too high, microglia undergo apoptosis or become trapped in a stalled, dysfunctional state—unable to finish engulfing plaque debris. Inhibition of INPP5D is currently one of the most exciting theoretical routes for restoring microglial competence, as shutting down this enzyme mathematically forces an increase in PIP3, artificially driving the cell into a hyper-phagocytic, hyper-resilient state.