MicroRNA-23a-3p improves neurological function in mice with traumatic brain injury by regulating microglial polarization

Abstract

BACKGROUND: Previous studies have demonstrated neuroprotective potential of microRNA-23a-3p in traumatic brain injury. However, direct evidence is still lacking regarding whether this protective effect stems from its precise regulation of the M1/M2 polarization balance of microglia. OBJECTIVE: To clarify the expression changes of microRNA-23a-3p in mouse brain tissue after traumatic brain injury and to explore the specific mechanism by which it affects neurological function through regulating microglial polarization. METHODS: Eighty C57BL/6J mice were randomly assigned to four groups: a sham operation group, a traumatic brain injury group, a traumatic brain injury + agomir-NC group, and a traumatic brain injury + agomir-MicroRNA-23a-3p group. The traumatic brain injury model was established using the cortical impact method. The sham group did not receive cortical impact. The intervention groups received intracerebroventricular injection of agomir-NC or agomir-MicroRNA-23a-3p after modeling. Six mice from the sham and traumatic brain injury groups were analyzed at 1, 3, 7, and 14 days post-injury, and six mice from the other two groups were analyzed at 14 days post-injury. Neurological deficits were assessed using the modified neurological severity score (mNSS). Hematoxylin-eosin staining and Nissl staining were used to observe pathological changes in brain tissue and neurons. qRT-PCR and western blot were used to detect the expression levels of MicroRNA-23a-3p, M1 markers (CD16, CD86), M2 markers (CD206, arginase-1), and inflammatory cytokines (tumor necrosis factor-α and interleukin-10). Immunohistochemistry was used to evaluate microglial M1/M2 polarization and the aggregation of F4/80-positive cells in the injured area. RESULTS AND CONCLUSION: Compared with the sham group, the expression of MicroRNA-23a-3p in the traumatic brain injury group showed a "V"-shaped curve, with downregulation in the early phase and upregulation starting at 7 days post-injury. Upregulation of MicroRNA-23a-3p reduced the mNSS score in traumatic brain injury mice. Morphological results showed that upregulation of MicroRNA-23a-3p alleviated brain edema and neuronal damage. Molecular biology results showed that upregulation of MicroRNA-23a-3p promoted microglial polarization from M1 to M2 phenotype. These findings indicate that MicroRNA-23a-3p can promote neurological function recovery after traumatic brain injury in mice by regulating microglial polarization.

1. Introduction

Traumatic brain injury (TBI) is caused by external mechanical forces leading to brain tissue damage. Depending on the mechanism and severity, it can range from mild concussion to severe neurological dysfunction and even death. TBI not only causes direct damage to the nervous system but also affects patients' physical and mental health, often resulting in long-term neurological deficits. Extensive research has revealed the mechanisms of secondary injury following TBI, including neuroinflammation, blood-brain barrier disruption, mitochondrial dysfunction, excitotoxicity, and apoptosis. Various therapeutic strategies have been explored, such as targeting microglia, inhibiting endoplasmic reticulum stress, modulating extracellular signal-regulated kinase signaling pathways, and applying novel nanomaterials. However, effective clinical interventions that precisely target these key processes and significantly improve patient outcomes remain lacking. Therefore, a deeper understanding of the molecular and cellular mechanisms underlying secondary brain injury is crucial for identifying new reliable diagnostic and therapeutic targets and ultimately improving patient prognosis.

The injury caused by TBI includes primary mechanical damage and a cascade of pathological events leading to secondary injury. In secondary injury, inflammation plays a pivotal role, with microglial activation and polarization being key factors in regulating immune responses and tissue repair. Microglia are the resident immune cells of the central nervous system, responsible for continuously monitoring the brain microenvironment, clearing pathological products, and maintaining tissue homeostasis. During TBI, microglia exhibit both M1 and M2 polarization, which have distinct functions: M1 microglia promote inflammation and exacerbate tissue damage, while M2 microglia are involved in anti-inflammatory responses and tissue repair. The balance between M1 and M2 polarization is critical for determining the outcome of injury and repair. Thus, modulating microglial polarization represents a promising therapeutic strategy for TBI.