Neuroinflammatory mediators play a crucial role in the pathophysiology of brain ischemia, exerting either deleterious effects on the progression of tissue damage or beneficial roles during recovery and repair. Within hours after the ischemic insult, increased levels of cytokines and chemokines enhance the expression of adhesion molecules on cerebral endothelial cells, facilitating the adhesion and transendothelial migration of circulating neutrophils and monocytes. These cells may accumulate in the capillaries, further impairing cerebral blood flow, or extravasate into the brain parenchyma. Infiltrating leukocytes, as well as resident brain cells, including neurons and glia, may release pro‐inflammatory mediators, such as cytokines, chemokines and oxygen/nitrogen free radicals that contribute to the evolution of tissue damage. Moreover, recent studies have highlighted the involvement of matrix metalloproteinases in the propagation and regulation of neuroinflammatory responses to ischemic brain injury. These enzymes cleave protein components of the extracellular matrix such as collagen, proteoglycan and laminin, but also process a number of cell‐surface and soluble proteins, including receptors and cytokines such as interleukin‐1β. The present work reviewed the role of neuroinflammatory mediators in the pathophysiology of ischemic brain damage and their potential exploitation as drug targets for the treatment of cerebral ischemia.

The innate immune system plays a dualistic role in the evolution of ischemic brain damage and has also been implicated in ischemic tolerance produced by different conditioning stimuli. Early after ischemia, perivascular astrocytes release cytokines and activate metalloproteases (MMPs) that contribute to blood–brain barrier (BBB) disruption and vasogenic oedema; whereas at later stages, they provide extracellular glutamate uptake, BBB regeneration and neurotrophic factors release. Similarly, early activation of microglia contributes to ischemic brain injury via the production of inflammatory cytokines, including tumor necrosis factor (TNF) and interleukin (IL)-1, reactive oxygen and nitrogen species and proteases. Nevertheless, microglia also contributes to the resolution of inflammation, by releasing IL-10 and tumor growth factor (TGF)-β, and to the late reparative processes by phagocytic activity and growth factors production. Indeed, after ischemia, microglia/macrophages differentiate toward several phenotypes: the M1 pro-inflammatory phenotype is classically activated via toll-like receptors or interferon-γ, whereas M2 phenotypes are alternatively activated by regulatory mediators, such as ILs 4, 10, 13, or TGF-β. Thus, immune cells exert a dualistic role on the evolution of ischemic brain damage, since the classic phenotypes promote injury, whereas alternatively activated M2 macrophages or N2 neutrophils prompt tissue remodeling and repair. Moreover, a subdued activation of the immune system has been involved in ischemic tolerance, since different preconditioning stimuli act via modulation of inflammatory mediators, including toll-like receptors and cytokine signaling pathways. This further underscores that the immuno-modulatory approach for the treatment of ischemic stroke should be aimed at blocking the detrimental effects, while promoting the beneficial responses of the immune reaction.

Autophagy is the major intracellular degradation pathway that regulates long-lived proteins and organelles turnover. This process occurs at basal levels in all cells but it is rapidly upregulated in response to starvation and cellular stress. Although being recently implicated in neurodegeneration, it remains still unclear whether autophagy has a detrimental or protective role. In this study, we investigated the dynamics of the autophagic process in retinal tissue that has undergone transient ischemia, an experimental model that recapitulates features of ocular pathologies, including glaucoma, anterior ischemic optic neuropathy and retinal vessels occlusion. Retinal ischemia, induced in adult rats by increasing the intraocular pressure, was characterized by a reduction in the phosphatidylethanolamine-modified form of LC3 (LC3II) and by a significant decrease in Beclin-1. The latter event was associated with a proteolytic cleavage of Beclin-1, leading to the accumulation of a 50-kDa fragment. This event was prevented by intravitreal treatment with the non-competitive N-methyl-D-aspartate antagonist MK801 and calpain inhibitors or by calpain knockdown. Blockade of autophagy by pharmacological inhibition or Beclin-1 silencing in RGC-5 increased cell death, suggesting a pro-survival role of the autophagic process in this neuronal cell type. Altogether, our results provide original evidence for calpain-mediated cleavage of Beclin-1 and deregulation of basal autophagy in the rat retina that has undergone ocular ischemia/reperfusion injury.