Role of miR-19a-3p and miR-19b-3p in microglia activation and neuroinflammation

Abstract

Background: Neuropathic pain induced by spinal cord injury (SCI) is a severe secondary health issue affecting up to 60% of individuals with SCI. Following SCI, activation of microglia, the immune cells of the central nervous system, triggers neuroinflammation through the production of pro-inflammatory cytokines, contributing to neuropathic pain. The relationship between inflammation and pain is well-established, and the neuroinflammatory effects of SCI are key to the chronic and intense pain experienced by many with SCI. MicroRNAs (miRNAs) have emerged as significant regulators of neuroinflammation. Previous research from our lab identified elevated levels of circulating miR-19a and miR-19b in individuals with SCI who suffer from neuropathic pain compared to those without pain. Purpose and Approach: This study aims to investigate the impact of miR-19a and miR-19b on microglia activation and neuroinflammation. The specific objectives are: 1) To determine the role of miR-19a-3p and miR-19b-3p in microglia activation, neuroinflammation, and the NF-κB and JAK-STAT signaling pathways following microglia activation. 2) To analyze the transcriptomic profiling of primary microglia and the effects of miR-19a-3p and miR-19b-3p on microglia activation and neuroinflammation. 3) To examine the impact of miR-19a-3p and miR-19b-3p on the expression of the neuroprotective genes Nurr1 (Nr4a2) and Nur77 (Nr4a1) following microglia activation and SCI. Results: Findings from Aim 1 revealed that mimics of miR-19a or miR-19b enhanced microglia activation, indicated by increased pro-inflammatory cytokine expression and decreased SOCS1 and SOCS3 expression. Additionally, miR-19a and miR-19b were found to enhance signaling through the NF-κB and JAK-STAT pathways. Aim 2 results showed that miR-19a and miR-19b modulate diverse gene expression patterns, regulate inflammation, and induce inflammatory responses in microglia as per RNA sequencing analysis. Aim 3 findings indicated that miR-19a and miR-19b decreased the expression of the neuroprotective genes Nurr1 and Nur77, with lower levels observed in the brains of SCI-rats. Summary: Findings from Aim 1 demonstrate that miR-19a or miR-19b treatment of microglia inhibits SOCS1 and SOCS3 expression, leading to increased pro-inflammatory cytokine expression and activation of NF-κB and JAK-STAT pathways. These results suggest that miR-19a and miR-19b activate microglia and elevate neuroinflammation. Evidence from Aim 2 shows that miR-19a and miR-19b induce distinct gene expression patterns and inflammatory profiles in microglia. This study highlights the importance of these miRNAs in microglia activation and neuroinflammation by examining their effects on gene and transcription factor expression in microglia. Aim 3 findings suggest that overexpression of miR-19a and miR-19b leads to reduced levels of Nurr1 and Nur77, correlating with enhanced inflammatory responses post-SCI. These results indicate that increased miR-19a and miR-19b following SCI may reduce Nurr1 and Nur77, thereby increasing the inflammatory response in microglia. Insights from this study may pave the way for developing miRNA-targeted therapies to modulate neuroinflammation and alleviate neuropathic pain in individuals with SCI.