FUNCTIONAL CHARACTERIZATION OF A RARE GENETIC VARIANT IN PHOSPHOLIPASE Cγ2 WHICH IS ASSOCIATED WITH A BENEFICIAL EFFECT ON THE PROGRESSION OF ALZHEIMER’S DISEASE

Abstract

PLCG2 is an important modulator of T- and B –lymphocyte mediated immune response and plays a crucial role in signal transmission by cleavage of 1-phosphatidylinositol-4,5-bisphosphate to diacylglycerol and inositol-3 phosphate, which further activates various PKC mediated signaling cascades. Receptor mediated activation of PLCG2 is controlled by receptor tyrosine kinases like BTK, LYN, GAB2, and TREM2, which makes of PLCG2 a good downstream modulator of signal cascades related to Alzheimer's disease (AD). Here, we functionally characterize a mutPLCG2 variant by cell biological and biochemical approaches. We also explore the effect of this variant on AD-relevant cerebrospinal fluid (CSF) biomarkers. Effect of mutPLCG2 construct was explored in transient transfected COS cell. Activation of PLCG2 variants were analyzed by both transfections with Btk or Rac2-G12V, or treatment with recombinant epidermal growth factor and a subsequent measurement of inositol phosphate level. In order to reduce clonal artefacts and ensure equal expression levels, stably PLCG2 WT and Mut expressing Hek FlpIn cells were generated for cell biological and biochemical experiments. Variant on PLCG2 was genotyped in a cohort of 1000 individuals with values for amyloid-beta 42, Tau and pTau levels on CSF. COS cells expressing transiently either PLCG2 WT or mutPLCG2 showed significant differences in inositol phosphate formation when transfected with bruton's tyrosine kinase or the constitutively active Rho GTPase, Rac2-G12V. Similar results were observed when PLCG2 activation was induced by EGF. Following experiments in stable HEK FlpIn cells showed no difference in protein expression level or migration between WT and mutPLCG2under control conditions. Further analysis of the PKCθ/NFκB pathway showed also no effects under control conditions. Next, we analyses the effect of this genetic variant on CSF levels of different biomarkers relevant for AD. We observed that carriers of the rare variant showed lower levels of pTau compared to non-carriers. Interestingly, this difference in pTau was stronger in mild cognitive impartments than in AD patients. Here we functionally characterized a rare variant in PLCG2 providing a potential link to the protective effect seen in AD. Additional experiments are currently underway and will be presented at the AAIC in London.