Background The ApoE4 genotype is the strongest genetic risk factor for developing AD. However, themechanisms that underlie this link between ApoE4 genotype and SAD are not well understood.Objective/Hypothesis The objectives are to understand the molecular underpinnings of the associationbetween ApoE4-specific changes in miRNA profile and ApoE4-induced brain phospholipid dysregulation whichleads to ApoE4 increased susceptibility to develop SAD. Our recent findings demonstrate that ApoE proteinsare critical determinants of brain phospholipid homeostasis and that the ApoE4 isoform is dysfunctional in thisprocess. We have found that the levels of PIP2 are reduced in human and mouse brains of ApoE4 carriers, andin primary neurons expressing ApoE4 alleles when compared to those levels in ApoE3 counterparts. Thesechanges are secondary to increased expression of a PIP2 degrading enzyme, the phosphoinositol phosphatasesynaptojanin 1 (synj1), in ApoE4 carriers. Genetic reduction of synj1 in ApoE4 mice restores PIP2 levels andmore importantly, rescues AD-related cognitive deficits. These findings are the first to link synj1 and PIP2homeostasis to the pathogenic effects of ApoE4 in sporadic AD. Further studies suggest that ApoE4 behaveslike the ApoE null conditions, which fails to degrade synj1 mRNA efficiently unlike ApoE3 does. We have alsofound that the levels of miR195 and miR374 are significantly lowered in ApoE4 mouse (9-12 months of age)and human brains (MCI and early AD subjects) compared to those in non-ApoE4 counterparts. Over-expression of miR195 but not miR374 in ApoE4 treated neurons reduces synj1 protein expression. Moreover,we have found that disruption of ApoE binding to its receptors LRP1 or genetic knockdown of LRP1 abolishesApoE-induced changes in miR195/synj1 pathways. Therefore, we hypothesize that ApoE3 binds to LRP1 toup-regulate miR195 expression which subsequently modulates synj1 mRNA degradation rate and synj1expression levels in the brain. In ApoE4 neurons and brains, decreased levels of miR195 may contribute to thereduced degradation rate of synj1 mRNA, thereby increasing synj1 protein expression and reduce brain PIP2levels. These changes may contribute to ApoE4-associated synaptic and cognitive dysfunction.Rationale/Experimental Design In this application, we will study the effects of specific miRNA changes onApoE4-associated phospholipid dyshomeostasis, synaptic dysfunction as well as cognitive dysfunction (aim 1).We will determine if elevating miR195 (which are low in ApoE4 mouse brains when compared to ApoE3counterparts) by intraventricular injection of viral-containing miRNAs, can correct phospholipiddyshomeostasis, and rescue synaptic and cognitive deficits in ApoE4 mice without and with AD transgenicbackground in vivo. We will also determine if inhibiting miR195 by antagomirs in ApoE3 mouse brains withoutAD transgenic background can result in phospholipid dysregulation and subsequent synaptic and cognitivedeficits, similarly to what we observed in ApoE4 mice. We propose to deliver miRNA-containing viral packagesor miRNA antagomirs to hippocampal regions of 3-month old mice, and to determine their cognitive function at6-9 months of age, as well as spine morphology and brain PIP2 homeostasis at 9-month of age. In aim 2, wepropose to determine the signaling pathways that link ApoE isoforms to LRP1 leading to changes in miR195and synj1 which contribute to ApoE4-related deficits. We propose to determine effects of miR195 on synj1transcript by luciferase assays, to identify binding motifs of synj1 3’-UTR regions for miR195, to determine thedownstream signal pathways from ApoE receptors to changes in miRNA and synj1 expression, and to identifykey drives and candidate genes important in regulating brain phospholipid homeostasis and cognitive functionafter miRNA manipulations in ApoE mouse brains using NGS data assembly and network prediction analysis.Relevance/Impact The studies proposed in this application could help us design therapeutic interventions forthe treatment of AD targeting at brain lipid homeostasis and ApoE4 through microRNA regulation.
|Effective start/end date||1/07/17 → 30/06/21|
- U.S. Department of Veterans Affairs: $150,000.00