CX3CR1-CCR2-dependent monocyte-microglial signaling modulates neurovascular leakage and acute injury in a mouse model of childhood stroke

Abstract

Stroke is among the top 10 causes of death in children. The developmental stage of the brain is central to stroke pathophysiology. The incidence of childhood arterial ischemic stroke (CAIS) is lower than of perinatal arterial ischemic stroke but the rate of recurrence is strikingly high. Vascular inflammation is seen as major contributor to CAIS but the mechanisms that govern structural-functional basis of vascular abnormalities remain poorly understood. To identify the contribution of immune-neurovascular interactions to CAIS, we established stroke model in postnatal day 21 (P21) mice. We demonstrate acute functional deficits and histological injury and chronic MRI-identifiable injury, brain atrophy and marked derangements in the vascular network. In contrast to negligible albumin leakage and neutrophil infiltration following acute perinatal stroke, CAIS leads to significantly increased albumin leakage and neutrophil infiltration in injured regions of wild type mice and mice with functional CX3CR1-CCR2 receptors. In mice with dysfunctional CX3CR1-CCR2 signaling, extravascular albumin leakage is significantly attenuated, infiltration of injurious Ccr2+-monocytes essentially aborted, accumulation of Ly6G+ neutrophils reduced and acute injury attenuated. Unique identifiers of microglia and monocytes revealed phenotypic changes in each cell subtype of the monocyte lineage after CAIS. Taken together, CX3CR1-CCR2-dependent microglia-monocyte signaling contributes to cerebrovascular leakage, inflammation and CAIS injury.

Mesenchymal stem cell therapy alleviates the neuroinflammation associated with acquired brain injury

“…Activated microglia and astrocytes prolong inflammation into the chronic phase via continued secretion of cytokines, chemokines, and CAMs, thus attracting more peripheral macrophages and neutrophils through the leaky BBB and other novel deleterious microglial and downstream signaling pathways. [21][22][23] Neuronal loss and cerebral edema may result from this progressive inflammation, compromising brain structure and function. 9,[19][20][21] Similar to stroke, the CNS following TBI undergoes a brief, neuroprotective phase during the acute inflammatory response following initial insult, yet this prosurvival stage is inadequate to provide neuroprotection for lasting inflammation.…”

“…[21][22][23] Neuronal loss and cerebral edema may result from this progressive inflammation, compromising brain structure and function. 9,[19][20][21] Similar to stroke, the CNS following TBI undergoes a brief, neuroprotective phase during the acute inflammatory response following initial insult, yet this prosurvival stage is inadequate to provide neuroprotection for lasting inflammation. 12 The principal injury induced by TBI is physical, involving damage to neurons and disturbances of the BBB.…”

“…Moreover, significant attenuation of both subacute and chronic inflammation may be achievable through cell-based therapy ( Figure 1). 4,[19][20][21] Subacute administration of cells aims to enable neuroprotection and preclude secondary cell death by ameliorating inflammation, apoptosis, mitochondrial dysfunction, and oxidative stress, while chronic delivery is intended to promote neuroregeneration by way of synaptogenesis, neurogenesis, angiogenesis, and vasculogenesis. Stimulation of these regenerative processes can mitigate inflammation and repair the BBB and other cerebral infrastructure.…”

Potential microglia‐based interventions for stroke

“…Dead/dying cells may also release a repertoire of signaling molecules such as purines, which are decrypted as “find me” and “eat me” signals by surrounding cells, including microglia, triggering subsequent microglia‐mediated phagocytosis and neuroprotection . Additionally, stroke‐exposed/stressed neurons can release “help‐me” signals comprised of a group of molecular determinants, including chemokines and cytokines such as CX3CL1, lipocalin‐2 (LCN2), fibroblast growth factor 2 (FGF2), IL‐34, and IgG . In a subarachnoid hemorrhage (SAH) model, FGF‐2 was determined to be a promising therapy to reduce neuronal apoptosis, acting as a “help‐me” signal through the activation of the FGFR3/PI3k/Akt signaling pathway …”

“…61 Additionally, stroke-exposed/ stressed neurons can release "help-me" signals 62 comprised of a group of molecular determinants, including chemokines and cytokines such as CX3CL1, lipocalin-2 (LCN2), fibroblast growth factor 2 (FGF2), IL-34, and IgG. 63 In a subarachnoid hemorrhage (SAH) model, FGF-2 was determined to be a promising therapy to reduce neuronal apoptosis, acting as a "help-me" signal through the activation of the FGFR3/ PI3k/Akt signaling pathway. 64 Moreover, other extracellular signals derived from microglia are linked.…”