Amyloid Beta Oligomers Prevents Lysosomal Targeting of miRNP to Stop Its Recycling and Target Cytokine Repression in Glial Cells

mRNAs encoding inflammatory cytokines are targeted by miRNAs and remain repressed in neuroglial cells. On exposure to amyloid beta 1-42 oligomers, glial cells start expressing proinflammatory cytokines although there has been increase in repressive miRNAs levels as well. Exploring the mechanism of this potential immunity of target cytokine mRNAs against repressive miRNAs in amyloid beta exposed glial cells, we have identified differential compartmentalization of repressive miRNAs in glial cells to explain this aberrant miRNA function. While the target mRNAs were found to be associated with polysomes attached to endoplasmic reticulum, the miRNPs found to be present predominantly with endosomes that failed to recycle to endoplasmic reticulum attached polysomes to repress mRNA targets in treated cells. Amyloid beta oligomers, by masking the Rab7 proteins on endosomal surface, affects Rab7 interaction with Rab Interacting Lysosomal Protein (RILP) on lysosomes to restrict endosomal maturation and its lysosomal targeting. This causes retarded miRNP targeting to lysosomes and recycling. Similar defects in miRNP retrieval has been observed in endosome maturation defective cells depleted for RILP or treated with Bafilomycin. RNA processing body localization of the miRNPs was also noted in treated cells that happens as a consequence of enhanced endosomal retention of miRNPs. Interestingly, depletion of P-body partly rescues the miRNA function in glial cells exposed to amyloid beta and restricts the excess cytokine expression there. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=71 SRC="FIGDIR/small/424324v1_ufig1.gif" ALT="Figure 1"> View larger version (17K): org.highwire.dtl.DTLVardef@1d9453dorg.highwire.dtl.DTLVardef@150a9c4org.highwire.dtl.DTLVardef@b99a1aorg.highwire.dtl.DTLVardef@1342676_HPS_FORMAT_FIGEXP M_FIG C_FIG Key PointsO_LIAmyloid beta exposure causes accumulation of inactive miR-146 miRNP to cause elevated proinflammatory cytokine production in glial cells. C_LIO_LIAmyloid beta masks Rab7-RILP interaction to reduce endosome lysosome interaction. C_LIO_LIAccumulated miRNPs failed to get targeted to lysosomes in amyloid exposed cells due to loss of endosome lysosome interaction C_LIO_LILysosomal compartmentalization of miRNPs is required for its recycling and repression of de novo targets C_LIO_LIAccumulated miRNPs are stored in P-Bodies and depletion of P-Bodies rescues miRNA function in amyloid exposed glial cells. C_LI