Balancing Anti-Inflammation and Neurorepair: The Role of Mineralocorticoid Receptor in Regulating Microglial Phenotype Switching After Traumatic Brain Injury

Background

As potent anti-inflammatory agents, glucocorticoids (GCs) have been widely used in the treatment of traumatic brain injury (TBI). However, their use remains controversial. Our previous study indicated that although dexamethasone (DEX) exerted anti-inflammatory effects and protected the blood–brain barrier (BBB) by activating the glucocorticoid receptor (GR) after TBI, it also impeded tissue repair processes due to excessive anti-inflammation. Conversely, fludrocortisone, acting as a specific mineralocorticoid receptor (MR) agonist, has shown potential in controlling neuroinflammation and promoting neurorepair, but the underlying mechanisms need further exploration.

Objective

This study aimed to explore the impact of the MR agonist fludrocortisone on microglia polarization, angiogenesis, functional rehabilitation, and associated mechanisms after TBI.

Methods

We established a mice controlled cortical impact model, and then immunofluorescence staining, western blot, rt-PCR, and MRI were performed to investigate microglia polarization, angiogenesis, and brain edema in the ipsilateral hemisphere after TBI and fludrocortisone treatment. Subsequently, functional tests including morris water maze, sucrose preference test, and forced swimming test were conducted to evaluate the effects of fludrocortisone treatment on neurofunction after TBI.

Results

Our results revealed that fludrocortisone suppressed neuroinflammation, enhanced angiogenesis and neuronal survival, and promoted functional rehabilitation by inducing a shift in microglia phenotype from M1 to M2 via the JAK/STAT6/PPARγ pathway. Additionally, the PI3K/Akt/HIF-1α pathway was involved in VEGF expression and in the process of angiogenesis.

Conclusion

Fludrocortisone, the specific MR agonist, exerted anti-neuroinflammatory and neuroprotective effects by regulating phenotypic switching of microglia from M1 to M2 rather than suppressing all types of microglia. Our study provided a theoretical basis for the therapeutic strategy of GCs targeting neuroinflammation after TBI.