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Zheng et al. Neuroimmunol Neuroinflammation 2019;6:1 Neuroimmunology and
DOI: 10.20517/2347-8659.2018.52 Neuroinflammation

Review Open Access

Microglial activation and polarization after
subarachnoid hemorrhage

Zhiyuan Vera Zheng, Kwok Chu George Wong

Division of Neurosurgery, Department of Surgery, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong, China.
Correspondence to: Dr. Kwok Chu George Wong, Division of Neurosurgery, Department of Surgery, Prince of Wales Hospital, The
Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China. E-mail: georgewong@surgery.cuhk.edu.hk
How to cite this article: Zheng ZV, Wong GKC. Microglial activation and polarization after subarachnoid hemorrhage.
Neuroimmunol Neuroinflammation 2019;6:1. http://dx.doi.org/10.20517/2347-8659.2018.52

Received: 31 Aug 2018 First Decision: 20 Sep 2018 Revised: 15 Oct 2018 Accepted: 30 Nov 2018 Published: 14 Jan 2019

Science Editor: Athanassios P. Kyritsis Copy Editor: Cui Yu Production Editor: Huan-Liang Wu

Abstract
Subarachnoid hemorrhage (SAH) is a devastating stroke type, with high mortality and morbidity. The
neuroinflammatory response evolves over time from early brain injury to delayed cerebral deterioration. Microglia,
the resident immune cells of the central nervous system, respond to the acute brain injury through activation and
polarization. Microglia are able to polarize along two pathways, classic M1 and alternative M2, towards tissue
injury and tissue repair respectively. The modulation of microglial activation has gained appreciation as a means to
prevent the detrimental effects. In this review, we describe the progression of microglial polarization after SAH and
summarize the key studies on mediators of microglial activation, including M1 and M2 specific microglial markers,
transcription factors and key signaling pathways. Interactions between microglia and other cells are critical in
modulating microglial activation and function, which are discussed as well. The preclinical application of microglia-
dependent treatments is presented, aiming for a better understanding of modulating microglial function and
suggesting future investigation for therapeutic approaches.

Keywords: Microglia, polarization, inflammation, mediator

INTRODUCTION
[1]
Subarachnoid hemorrhage (SAH) is a devastating condition accounting for 5% of the stroke population .
The mortality rate is as high as 30%-40% and approximately 50% of the survivors remain permanently
[2,3]
disabled . Primary brain damage develops within the first few hours to days after SAH as a result of
extravasate blood or intracranial circulatory arrest. The increased intracerebral pressure and mass effect
result in the sudden herniation and death. Recently, more attention has been focused on early brain injury
[4]
(EBI) which appear to contribute to subsequent adverse cerebral events . Current treatment for SAH mainly
© The Author(s) 2019. Open Access This article is licensed under a Creative Commons Attribution 4.0
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