Vitamin D promotes neurological recovery via enhancing haematoma clearance in experimental intracerebral haemorrhage

Abstract

Intracerebral haemorrhage is one of the most devastating types of stroke with high mortality and morbidities. Haematoma triggers a cascade of reactions resulting in primary and secondary brain injuries, making haematoma clearance the primary goal in ICH treatment. Surgical removal of haematoma is an option in specific cases, but its efficiency remains controversial. Herein, pharmacological agents that alleviate the haematoma burden are in need. Upon ICH, rapidly recruited macrophage/microglia (Mφ) could uptake erythrocyte via erythrophagocytosis. Erythrophagocytosis can reduce erythrocyte lysis and the release of toxic lysis products. Mechanistically, nuclear factor peroxisome proliferator-activated receptor gamma (PPAR γ) in Mφ orchestrates erythrophagocytosis via transcriptionally upregulating scavenger receptor (e.g.,CD36). Mφ encompasses resident microglia and infiltrating monocyte-derived macrophage. In stroke, the circulating monocytes fuel the macrophage pool after undergoing in-situs differentiation. Furthermore, the reparative phenotype (M2) Mφ facilitates haematoma resolution and functional recovery, Collectively, boosting the erythrophagocytosis ability of microglia/macrophage and/or increasing the M2 Mφ may serve as therapeutic approaches to enhance haematoma resolution in ICH. Vitamin D (VitD), a fat-soluble hormone, has gained increasing research interests in its functions with the central nervous system and immune system. In observational studies, VitD status was noticed to negatively correlate with stroke severity. The roles of VitD on the immune system were mainly found on Mφ. On one hand, VitD added to the innate immunity by enhancing phagocytosis of Mφ. On the other hand, the bioactive form of VitD served as the endogenous inducer of macrophage maturation during monocytes differentiation. Therein, VitD could boost the phagocytosis and the pool of Mφ in the lesion site. However, no study of the effect of VitD supplementation on ICH has been reported to date. In this study, VitD, for the first time, was proved to restore neurological function in mice after ICH. VitD significantly reduced haematoma volume on day 3, day 5, and day 7. This indicated VitD treatment resulted in faster haematoma clearance. This candidate also observed similar results in middle-aged mice. To interrogate the underlying mechanism, this study investigated the effect of VitD on Mφ mediated-erythrophagocytosis. Western blot of lesion tissues showed that VitD treatment elevated the expression levels of PPAR γ and downstream effector CD36. However, both in vivo and primary culture studies found that VitD insignificantly affected the CD36 expression and phagocytosis of Mφ. Instead, VitD increased monocyte differentiation toward macrophage in ICH. An in-vitro study proved VitD primed bone marrow cells differentiation into M2 macrophage, the essential Mφ directing erythrophagocytosis. Importantly, this candidate found macrophages were the major cell type performing erythrophagocytosis together with high CD36 expression. Thus, the increased number of macrophages might account for the increased PPAR γ/CD36 axis and haematoma clearance in vivo. In this proof-of-concept study, this candidate demonstrated that VitD accelerated haematoma clearance and reserved neurobehavior function in the animal models after ICH. This study provided a highly translational therapeutic option using a clinically feasible treatment time window. Further studies are needed to determine VitD supplementation as a clinically viable strategy to treat ICH.