Prion protein N1 cleavage peptides stimulate microglial interaction with surrounding cells

J A Carroll,C L Haigh,B R Groveman,B Race,R Moore,K Williams

doi:10.1038/s41598-020-63472-z

Abstract

Microglia act as the protective immune cell of the brain. By surveying the tissue to identify and rectify problems, they function to maintain the health of brain cells. The prion protein N-terminal cleavage fragment, N1, has demonstrated neuroprotective activities in vitro and in vivo. This study aimed to elucidate whether N1 could modulate microglial function and, if so, determine the consequences for the surrounding tissue. Using a mixed neuronal lineage and microglia co-culture system, we showed that N1 stimulation changed overall morphology and metabolism, suggesting enhanced cellular viability. Furthermore, N1 induced an increase in Cxcl10 secretion in the co-cultures. Recombinant Cxcl10, administered exogenously, mediated the changes in the mixed neuronal lineage culture morphology and metabolism in the absence of microglia, but no effect of Cxcl10 was observed on microglia cultured on their own. Direct cell-to-cell contact was required for N1 to influence microglia in the co-cultures, and this was linked with restructuring of microglial membrane composition to include a higher GM1 content at interaction sites with surrounding cells. Our findings show that N1 can play a regulatory role in microglial function in the context of an inter-connected network of cells by changing both cellular interaction sites and cytokine secretion.

Highlights

Microglia act as the protective immune cell of the brain
Despite no consensus regarding the function of prion protein (PrP), numerous studies have linked it with neuroprotection
We devised a co-culture system to investigate the influence of the PrP N-terminal cleavage fragment, N1, on microglia function and the consequences for other brain cell types

Summary

Introduction

Microglia act as the protective immune cell of the brain. By surveying the tissue to identify and rectify problems, they function to maintain the health of brain cells. When subjected to an insult, for example ischemic infarct, PrP knock-out mice suffer greater damage and when PrP is over-expressed damage is reduced compared with wild type mice[16,17] Both the α- and β-cleavages have been linked with neuroprotection[18] and the N1 and N2 N-terminal secretory fragments exhibit their own neuroprotective activities[11,19,20,21]. N1, N2 or both peptides have shown the capacity to modulate intracellular reactive oxygen species (ROS), signal transduction through MEK1 and p53, changes in plasma membrane lipids and mitochondrial fission[11,19,21,22] Several of these factors are activators of MG23–25, the N1 and N2. The neuroprotection conferred by N1 in AD is thought to be due to direct binding and this aspect of N1 biology is currently under investigation as a potential therapeutic avenue[26,27,28,29]

Objectives

Methods

Results

Conclusion