Identification of Multipotent Stem Cells in Human Brain Tissue Following Stroke

Perivascular regions of the brain harbor multipotent stem cells. We previously demonstrated that brain pericytes near blood vessels also develop multipotency following experimental ischemia in mice and these ischemia-induced multipotent stem cells (iSCs) can contribute to neurogenesis. However, it is essential to understand the traits of iSCs in the poststroke human brain for possible applications in stem cell-based therapies for stroke patients. In this study, we report for the first time that iSCs can be isolated from the poststroke human brain. Putative iSCs were derived from poststroke brain tissue obtained from elderly stroke patients requiring decompressive craniectomy and partial lobectomy for diffuse cerebral infarction. Immunohistochemistry showed that these iSCs were localized near blood vessels within poststroke areas containing apoptotic/necrotic neurons and expressed both the stem cell marker nestin and several pericytic markers. Isolated iSCs expressed these same markers and demonstrated high proliferative potential without loss of stemness. Furthermore, isolated iSCs expressed other stem cell markers, such as Sox2, c-myc, and Klf4, and differentiated into multiple cells in vitro, including neurons. These results show that iSCs, which are likely brain pericyte derivatives, are present within the poststroke human brain. This study suggests that iSCs can contribute to neural repair in patients with stroke.

Introduction
Ischemic stroke often results in severe and irreversible central nervous system (CNS) dysfunction. While increasing numbers of stroke patients now benefit from treatments such as neuroendovascular intervention and thrombolytic therapy [1,2], many still suffer from permanent sequela due to the limited time window for these therapies and frequent unsuccessful recanalization.

Stem cell-based therapies have emerged as a promising alternative therapeutic option for patients with ischemic stroke. Among several types of stem cells, neural stem/progenitor cells (NSPCs) are a strong therapeutic candidate because they can differentiate into various neural cell types, including neurons. Accumulating evidence indicates that NSPCs are present not only in the rodent [3–7] but also in the human CNS [8–10]. Previous rodent experiments have also demonstrated that many cell types in the healthy mature brain, such as astrocytes in the subventricular zone (SVZ) [3,4], ependymal cells [7], oligodendrocyte precursor cells [5], and resident glia [11], are potential sources of NSPCs.

Although the precise origin of NSPCs under pathological conditions remains unclear, using a mouse model of cerebral infarction, we previously reported that brain pericytes near blood vessels developed multipotent stem cell activity in response to ischemia/hypoxia and differentiated into various neural lineages [12,13]. These results indicate that ischemia-induced multipotent stem cells (iSCs) originating from pericytes (iPCs) function as NSPCs in mice and may contribute to neural regeneration [12–14].

However, it remains unclear if pericytes can also transition to multipotency in human brain following stroke. Moreover, it is essential to understand the regulation of human iSC proliferation and differentiation for possible applications in stem cell-based stroke therapy. Although our previous study identified nestin+ cells presumably containing iSC populations in poststroke human autopsied brains [15], there is still no direct evidence that iSCs are present or induced within the poststroke human brain.

In this study, using brain samples obtained from stroke patients who needed partial lobectomy as well as decompressive craniectomy for diffuse cerebral infarction, we investigated whether iSCs can be isolated from the poststroke human brain. We then examined the localization, gene expression patterns, proliferative potential, and multipotency of human iSCs.