Buyang Huanwu decoction promotes gray and white matter remyelination by inhibiting Notch signaling activation in the astrocyte and microglia after ischemic stroke

Abstract

Ethnopharmacological relevance

Ischemic stroke causes damages to both gray and white matter, resulting in long-term motor impairments. Myelin repair is a promising strategy for poststroke motor rehabilitation. Buyang Huanwu Decoction (BHD) is a classical traditional Chinese medicine formula for managing the sequelae of ischemic stroke. Whether BHD benefits gray and white matter remyelination following stroke remains to be elucidated.

Aim of the study

The present study aimed to investigate the effects of BHD on the gray and white matter remyelination following ischemic stroke and further explore the underlying mechanisms by combining magnetic resonance imaging (MRI) and histological experiments.

Materials and methods

The ischemic stroke model was established in male Sprague-Dawley rats by permanently occluding the middle cerebral artery (MCAO). BHD (16.6 g/kg and 8.3 g/kg) was intragastrically administered to rats for 30 days. The motor function was assessed by an automated Digi gait system. The structural integrity of the motor cortex and external capsule was monitored by MRI, including T2 mapping and diffusion tensor imaging (DTI). The remyelination was examined by Olig2/Ki67, 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNPase)/Ki67 double immunofluorescence staining and Luxol fast blue (LFB) staining. Subsequently, the Notch signaling activation in astrocytes and microglia was assessed by double immunofluorescence staining with JAG1/Notch1/Notch intracellular domain (NICD) and glial fibrillary acidic protein (GFAP)/ionized calcium binding adaptor molecule 1 (Iba1).

Results

BHD treatments remarkably improved motor function of the MCAO rats by reducing steps, swing time and ataxia coefficient of the left forelimb. The MRI examinations found that BHD treatments significantly reduced infarct volume and preserved the motor cortex and external capsule integrity, as reflected by decreased T2 values, RD, and increased FA. Notably, the gait parameters of the left forelimb were correlated to the MRI index obtained from the perilesional motor cortex and external capsule to varying degrees. Furthermore, BHD treatments enhanced gray and matter remyelination by elevating the numbers of Olig2⁺/Ki67⁺, CNPase⁺/Ki67⁺ cells, and the integrated optical density of LFB. Finally, BHD effectively inhibited the activation of Notch signaling in the astrocytes and microglia of the corresponding gray and white matter, as evidenced by decreased numbers of cells co-expressing JAG1/Notch1/NICD and GFAP/Iba1.

Conclusion

This study demonstrated that BHD treatment could promote poststroke motor recovery by preserving the structural integrity of the gray and white matter and facilitating their remyelination. Notably, the pro-remyelination effects of BHD treatment might be attributed to suppressed activation of Notch signaling within the reactive astrocytes and microglia.