Metabotropic glutamate receptor subtype 5 is altered in LPS-induced murine neuroinflammation model and in the brains of AD and ALS patients

PurposeThe aim of the present study was to determine the expression levels of mGluR5 in different mouse strains after induction of neuroinflammation by lipopolysaccharide (LPS) challenge and in the brains of patients with Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS) post mortem to investigate mGluR5 expression in human neurodegenerative diseases.MethodsC57BL/6 and CD1 mice were injected intraperitoneally with either 10mg/kg LPS or saline. mGluR5 and TSPO mRNA levels were measured after 1 and 5days by qPCR, and mGluR5 protein levels were determined by PET imaging with the mGluR5-specific radiotracer [F-18]PSS232. mGluR5 expression was evaluated in the post-mortem brain slices from AD and ALS patients using in vitro autoradiography.ResultsmGluR5 and TSPO mRNA levels were increased in brains of C57BL/6 and CD1 mice 1day after LPS treatment and remained significantly increased after 5days in C57BL/6 mice but not in CD1 mice. Brain PET imaging with [F-18]PSS232 confirmed increased mGluR5 levels in the brains of both mouse strains 1day after LPS treatment. After 5days, mGluR5 levels in CD1 mice declined to the levels in vehicle-treated mice but remained high in C57BL/6 mice. Autoradiograms revealed a severalfold higher binding of [F-18]PSS232 in post-mortem brain slices from AD and ALS patients compared with the binding in control brains.ConclusionLPS-induced neuroinflammation increased mGluR5 levels in mouse brain and is dependent on the mouse strain and time after LPS treatment. mGluR5 levels were also increased in human AD and ALS brains in vitro. PET imaging of mGluR5 levels could potentially be used to diagnose and monitor therapy outcomes in patients with AD and ALS.