P2Y6 receptor inhibition aggravates ischemic brain injury by reducing microglial phagocytosis

Abstract

Background Clearance of damaged cells is beneficial for the functional recovery after brain injury. Phagocytosis of tissue and cell debris is an important function of microglia during the development and pathological diseases. However, which specific phagocytic receptor mediates microglial phagocytosis after ischemic stroke is obscure. Methods ICR mice (n=59) underwent 90 minutes transient middle cerebral artery occlusion. P2Y6R, Iba1, GFAP and Tuj-1 double immunostainings were performed to determine P2Y6 receptor location. MRS2578 was injected into mice to inhibit P2Y6 receptor activity. Iba1 and TUNEL staining were performed to examine microglia phagocytosis. Modified neurological severity scores and Grid walking test were used to evaluate the neurological function after ischemic stoke. The expression of IL-1 α, IL-1 β, IL-6, IL-10, TNF-α, TGF-β and MPO was used to examine the inflammation response in the brain. Results The expression of P2Y6 receptor in microglia increased within three days after transient middle cerebral artery occlusion. Inhibition of microglial phagocytosis by the selective inhibitor MRS2578 enlarged the brain atrophy and edema volume after ischemic stroke, subsequently aggravated neurological function using modified neurological severity scores and Grid walking test. MRS2578 treatment had no effect on the expression of IL-1α, IL-1β, IL-6, IL-10, TNF-α, TGF-β and MPO after ischemic stroke, which suggested that it had no effect on the inflammation in the brain. Finally, we found that the expression of myosin light chain kinase decreased after microglial phagocytosis inhibition in ischemic mice, which suggested that myosin light chain kinase was involved in P2Y6 receptor mediated phagocytosis. Conclusion Our results indicated that the P2Y6 receptor mediated microglial phagocytosis played an important role during the acute stage of ischemic stroke, which was a potential target for ischemic stroke treatment.

Microglial/Macrophage polarization and function in brain injury and repair after stroke

“…Under pathological conditions, microglia are a critical component of the innate immune sentinel network and serve as the first line of defense in the CNS. Phagocytosis is an established microglial function designed for removal of cellular debris or dead cells, without necessarily initiating an inflammatory response 31,32 . Microglia quickly detect pathogens, including bacteria, fungi, and viruses that enter the brain parenchyma and respond by producing pro‐ and/or anti‐inflammatory cytokines, chemokines, and complement proteins.…”

DHA modulates MANF and TREM2 abundance, enhances neurogenesis, reduces infarct size, and improves neurological function after experimental ischemic stroke

“…Microglial activation is a neural defense against damage triggered by brain ischemia 9 . Ischemic stroke perturbs endogenous inhibitory signaling and triggers microglial activation 10 that either aggravates ischemic injury or induces repair and regeneration, depending on the different signals received by microglial receptors 10,11 . TREM2 abundance on the microglia cell surface is 300 times higher than on astrocytes 12 .…”

Neurovascular Unit: A critical role in ischemic stroke

“…Microglia also display both pro‐ and anti‐inflammatory phenotypes (named M1 and M2, respectively) and respond rapidly to ischemia during IS 53,54 . Within one day after IS, the proliferation and activation of microglia induced a strong inflammatory response (upregulation of TNF, IL‐1β, and IL‐6), causing severe damage to the CNS 51,55 .…”