Background and Purpose: The immune system responds rapidly following ischemic brain injury and can contribute to the final extent of brain damage. microRNA are differentially expressed in leukocytes following ischemic stroke and may regulate the immune response to ischemic brain injury. In this study we evaluate microRNA let7i-5p in ischemic stroke and its regulation of leukocytes.
Methods: A total of 212 patients were studied; 106 with acute ischemic stroke and 106 risk factor matched controls. . RNA from circulating leukocytes was isolated from blood collected in PaxGene tubes. Let7i-5p miRNA expression was assessed by Taqman qRT-PCR. Given microRNAs act to destabilize and degrade their target mRNA, mRNA that inversely correlated with let7i were identified. To demonstrate let7i post-transcriptional regulation of target genes, a 3’UTR luciferase assay was performed. Target protein expression was assessed by ELISA.
Results: Let7i was decreased in patients with acute ischemic stroke (fold change -1.70, p<0.00001). A modest inverse correlation between let7i and NIH Stroke Scale at admission (r= -0.32, p=0.02), infarct volume (r= -0.21, p=0.04) and plasma MMP9 (r= -0.46, p=0.01) was identified. The decrease in let7i was associated with increased expression of several of its messenger RNA targets including CD86, CXCL8 and HMGB1. In vitro studies confirm let7i post-transcriptional regulation of target genes CD86, CXCL8 and HMGB1. Functional analysis predicted let7i regulates pathways involved in leukocyte activation, recruitment, and proliferation including canonical pathways CD86 signaling in T helper cells, HMGB1 signaling, and CXCL8 signaling.
Conclusions: Let7i is decreased in circulating leukocytes of patients with acute ischemic stroke. Mechanisms by which let7i regulates inflammatory response post-stroke include targeting CD86, CXCL8 and HMGB1.