Hepatic LRP-1 plays an important role in amyloidosis in Alzheimer’s disease mice: Potential role in chronic heavy alcohol feeding

Abstract

Background: Hepatic lipoprotein receptor-related protein 1 (LRP-1) plays a central role in peripheral Aβ clearance, but its importance in Alzheimer’s disease (AD) pathology is understudied. Our previous work showed that intragastric alcohol feeding to C57BL/6Jmice reduced hepatic LRP-1 expression which correlated with significant AD-relevant changes in the brain. Herein, we examined the role of hepatic LRP-1 in AD pathogenesis in APP/PS1 AD mice using two approaches to modulate hepatic LRP-1, intragastric alcohol feeding to model chronic heavy drinking shown by us to reduce hepatic LRP-1, and hepato-specific LRP-1 silencing; both approaches have never been attempted in AD mice. Methods: Eight-month-old male APP/PS1 mice were fed ethanol or control diet intragastrically for 5 weeks (n=7-11/group). Brain and liver Aβ were assessed using immunoassays. Three important mechanisms of brain amyloidosis were investigated: hepatic LRP-1 (major peripheral Aβ regulator), blood-brain barrier (BBB) function (vascular Aβ regulator), and microglia (major brain Aβ regulator) using immunoassays. Spatial LRP-1 gene expression in the periportal versus pericentral hepatic regions was confirmed using NanoString GeoMx Digital Spatial Profiler. Further, hepatic LRP-1 was silenced by injecting LRP-1 microRNA delivered by the adeno-associated virus 8 (AAV8) and the hepato-specific thyroxine-binding globulin (TBG) promoter to 4-month-old male APP/PS1 mice (n=6). Control APP/PS1 mice received control AAV8 (n=6). Spatial memory and locomotion were assessed 12 weeks after LRP-1 silencing using Y-maze and open-field test, respectively, and brain and liver Aβ were measured. Results: Alcohol feeding reduced plaque-associated microglia in APP/PS1 mice brains and increased aggregated Aβ (p<0.05) by ELISA and 6E10-positive Aβ load by immunostaining (p<0.05). Increased brain Aβ corresponded with a significant downregulation of hepatic LRP-1 (p<0.01) at the protein and transcript level, primarily in pericentral hepatocytes (zone 3) where alcohol-induced injury occurs. Hepato-specific LRP-1 silencing significantly increased brain Aβ and locomotion hyperactivity (p<0.05) in APP/PS1 mice. Conclusion: Chronic heavy alcohol intake reduced hepatic LRP-1 expression and increased brain Aβ. The hepato-specific LRP-1 silencing similarly increased brain Aβ which was associated with behavioral deficits in APP/PS1 mice. Collectively, our results suggest that hepatic LRP-1 is a key regulator of brain amyloidosis in alcohol-dependent AD.