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Role of spleen-derived monocytes/macrophages in acute ischemic brain injury.

ABSTRACT: Monocytes/macrophages (MMs), mononuclear phagocytes, have been implicated in stroke-induced inflammation and injury. However, the presence of pro-inflammatory Ly-6C(high) and antiinflammatory Ly-6C(low) monocyte subsets raises uncertainty regarding their role in stroke pathologic assessment. With recent identification of the spleen as an immediate reservoir of MMs, this current study addresses whether the spleen-derived MMs are required for stroke pathologic assessment. We observed that the spleen was contracted in poststroke animals and the contraction was accompanied by decreased number of Ly-6C(high) and Ly-6C(low) subsets in the spleen. The deployment of these subsets from the spleen temporally coincided with respective increases in the ischemic brain. Compared to mice with the spleen, mice receiving a splenectomy just before the stroke displayed less accumulation of Ly-6C(high) and Ly-6C(low) MMs in the brain. Despite the reduced accumulation of both subsets, infarct size and swelling were not reduced in the asplenic mice. The dissociative findings of infarct size and extent of MM infiltration in the postischemic brain indicate minimal involvement of spleen-derived total MMs in acute infarct development. Selective Ly-6C(high) or Ly-6C(low) MM targeting is suggested to address the contribution of the individual subset to acute stroke pathologic assessment.

SUBMITTER: Kim E

PROVIDER: S-EPMC4126087 | biostudies-other | 2014 Aug

REPOSITORIES: biostudies-other

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Role of spleen-derived monocytes/macrophages in acute ischemic brain injury.

Kim Eunhee E Yang Jiwon J Beltran Cesar D CD Cho Sunghee S

Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism 20140528 8

Monocytes/macrophages (MMs), mononuclear phagocytes, have been implicated in stroke-induced inflammation and injury. However, the presence of pro-inflammatory Ly-6C(high) and antiinflammatory Ly-6C(low) monocyte subsets raises uncertainty regarding their role in stroke pathologic assessment. With recent identification of the spleen as an immediate reservoir of MMs, this current study addresses whether the spleen-derived MMs are required for stroke pathologic assessment. We observed that the sple ...[more]

PMID: 24865998

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Project description:Exposure to low-dose lipopolysaccharide (LPS) before cerebral ischemia is neuroprotective in stroke models, a phenomenon termed preconditioning (PC). Although it is well established that LPS-PC induces central and peripheral immune responses, the cellular mechanisms modulating ischemic injury remain unclear. Here, we investigated the role of immune cells in the brain protection afforded by PC and tested whether monocytes may be reprogrammed by ex vivo LPS exposure, thus modulating inflammatory injury after cerebral ischemia in male mice. We found that systemic injection of low-dose LPS induces a Ly6Chi monocyte response that protects the brain after transient middle cerebral artery occlusion (MCAO) in mice. Remarkably, adoptive transfer of monocytes isolated from preconditioned mice into naive mice 7 h after transient MCAO reduced brain injury. Gene expression and functional studies showed that IL-10, inducible nitric oxide synthase, and CCR2 in monocytes are essential for neuroprotection. This protective activity was elicited even if mouse or human monocytes were exposed ex vivo to LPS and then injected into male mice after stroke. Cell-tracking studies showed that protective monocytes are mobilized from the spleen and reach the brain and meninges, where they suppress postischemic inflammation and neutrophil influx into the brain parenchyma. Our findings unveil a previously unrecognized subpopulation of splenic monocytes capable of protecting the brain with an extended therapeutic window and provide the rationale for cell therapies based on the delivery of autologous or allogeneic protective monocytes in patients after ischemic stroke.SIGNIFICANCE STATEMENT Inflammation is a key component of the pathophysiology of the brain in stroke, a leading cause of death and disability with limited therapeutic options. Here, we investigate endogenous mechanisms of protection against cerebral ischemia. Using lipopolysaccharide (LPS) preconditioning (PC) as an approach to induce ischemic tolerance in mice, we found generation of neuroprotective monocytes within the spleen, from which they traffic to the brain and meninges, suppressing postischemic inflammation. Importantly, systemic LPS-PC can be mimicked by adoptive transfer of in vitro-preconditioned mouse or human monocytes at translational relevant time points after stroke. This model of neuroprotection may facilitate clinical efforts to increase the efficacy of BM mononuclear cell treatments in acute neurological diseases such as cerebral ischemia.

Dataset Information

Role of spleen-derived monocytes/macrophages in acute ischemic brain injury.

Publications

Role of spleen-derived monocytes/macrophages in acute ischemic brain injury.

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