CD36, a class-B scavenger receptor involved in multiple functions, including inflammatory signaling, may also contribute to ischemic brain injury through yet unidentified mechanisms. We investigated whether CD36 participates in the molecular events underlying the inflammatory reaction that accompanies cerebral ischemia and may contribute to the tissue damage. We found that activation of nuclear factor-κB, a transcription factor that coordinates postischemic gene expression, is attenuated in CD36-null mice subjected to middle cerebral artery occlusion. The infiltration of neutrophils and the glial reaction induced by cerebral ischemia were suppressed. Treatment with an inhibitor of inducible nitric oxide synthase, an enzyme that contributes to the tissue damage, reduced ischemic brain injury in wild-type mice, but not in CD36 nulls. In contrast to cerebral ischemia, the molecular and cellular inflammatory changes induced by intracerebroventricular injection of interleukin-1β were not attenuated in CD36-null mice. The findings unveil a novel role of CD36 in early molecular events leading to nuclear factor-κB activation and postischemic inflammation. Inhibition of CD36 signaling may be a valuable therapeutic approach to counteract the deleterious effects of postischemic inflammation.

Loss-of-function mutations of progranulin (PGRN) have been linked to frontotemporal dementia, but little is known about the effects of PGRN deficiency on the brain in health and disease. PGRN has been implicated in neurovascular development, inflammation, and Wnt signaling, a pathway involved in the formation of the blood–brain barrier (BBB). Because BBB alterations and inflammation contribute to ischemic brain injury, we examined the role of PGRN in the brain damage produced by ischemia-reperfusion.PGRN^+/−andPGRN^−/−mice underwent middle cerebral artery occlusion (MCAO) with monitoring of cerebral blood flow. Infarct volume and motor deficits were assessed 72 h later. Post-ischemic inflammation was examined by expression of inflammatory genes and flow cytometry. BBB structure and permeability were examined by electron microscopy (EM) and Evans blue (EB) extravasation, respectively. MCAO resulted in ∼60% larger infarcts inPGRN^+/−andPGRN^−/−mice, an effect independent of hemodynamic factors or post-ischemic inflammation. Rather, massive hemorrhages and post-ischemic BBB disruption were observed, unrelated to degradation of tight junction (TJ) proteins or matrix metalloproteinases (MMPs). By EM, TJ were 30–52% shorter, fewer, and less interlocking, suggesting a weaker seal between endothelial cells. Intracerebral injection of platelet-derived growth factor-CC (PDGF-CC), which increases BBB permeability, resulted in a more severe BBB breakdown inPGRN^+/−andPGRN^−/−than wild-type mice. We describe a previously unrecognized involvement of PGRN in the expression of key ultrastructural features of the BBB. Such a novel vasoprotective role of PGRN may contribute to brain dysfunction and damage in conditions associated with reduced PGRN function.

Protein aggregation critically affects cell viability in neurodegenerative diseases, but whether this also occurs in ischemic brain injury remains elusive. Prior studies report the post-ischemic aggregation of ubiquitin, small ubiquitin-related modifier (SUMO) and ribosomes, however whether other proteins are also affected is unknown. Here we employed a proteomic approach to identify the insoluble, aggregated proteome after cerebral ischemia. Mice underwent transient middle cerebral artery occlusion or sham-surgery. After 1-hour reperfusion, prior to apparent brain injury, mice were sacrificed and detergent-insoluble proteins were obtained and identified by nanoLC-MS/MS. Naturally existing insoluble proteins were determined in sham controls and aggregated proteins after cerebral ischemia/reperfusion were identified. Selected aggregated proteins found by proteomics were biochemically verified and aggregation propensities were studied during ischemia with or without reperfusion. We found that ischemia/reperfusion induces the aggregation of RNA-binding and heat-shock proteins, ubiquitin, SUMO and other proteins involved in cell signalling. RNA-binding proteins constitute the largest group of aggregating proteins in ischemia. These include TDP43, FUS, hnRNPA1, PSF/SFPQ and p54/NONO, all of which have been linked to neurodegeneration associated with amyotrophic lateral sclerosis and frontotemporal dementia. The aggregation of neurodegeneration-related disease proteins in cerebral ischemia unveils a previously unappreciated molecular overlap between neurodegenerative diseases and ischemic stroke.