Published online Jul 26, 2020. doi: 10.4252/wjsc.v12.i7.633
Peer-review started: January 20, 2020
First decision: March 24, 2020
Revised: April 4, 2020
Accepted: May 15, 2020
Article in press: May 15, 2020
Published online: July 26, 2020
Bone marrow mesenchymal stem cells (BMSCs) have been widely studied for their applications in stem-cell-based stroke therapy. Although anti-inﬂammatory and paracrine effects of grafted BMSCs have been shown, the precise mechanism underlying BMSCs-induced M2 microglia polarization remains unclear. Mesencephalic astrocyte-derived neurotrophic factor (MANF) is a new member of the neurotrophic factor families, which is upregulated during endoplasmic reticulum (ER) stress and protects several cell populations from ER-stress-induced cell death in vivo or in vitro.
MANF and platelet-derived growth factor (PDGF)-AA/MANF signaling have been shown to have an immunoregulatory effect on M1/M2 macrophage differentiation to promote damage repair and neuroprotective effect.
In the present study, the aim was to detect whether MANF paracrine signaling mediated BMSCs-induced M2 polarization and to determine the molecular mechanism underlying the PDGF-AA/MANF signaling pathway.
We first identified the secretion of MANF by BMSCs and developed genetically modified BMSCs that downregulated MANF expression. BMSCs were injected into the right striatum 24 h before cerebral ischemia/reperfusion injury. Using a rat middle cerebral artery occlusion (MCAO) model and BMSCs/microglia Transwell coculture system, the effect of BMSCs-mediated MANF paracrine signaling on M1/M2 polarization in vivo and in vitro was determined by Western blot, quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and immunofluo-rescence. The transgenic microglia were used to assess the effect of miR-30a* on PDGF-AA/miR-30a*/X-box binding protein (XBP) 1/MANF signaling pathway. Western blot and qRT-PCR were conducted to examine the expression of ER stress-related markers.
In vivo or in vitro, BMSCs induced functional recovery and increased M2 marker expression, as well as decreased expression of M1 marker, which were inhibited by MANF siRNA treatment. As another soluble factor secreted by BMSCs, PDGF-AA upregulated XBP1 and MANF expression via downregulating miR-30a* in the activated microglia.
BMSCs promote M2 phenotype polarization through MANF secretion, which might partially contribute to the functional outcomes in stroke rats. Besides MANF paracrine signaling, the PDGF-AA/miR-30a*/XBP1/MANF signaling pathway influences BMSCs-mediated M2 polarization.
These findings will be beneficial in development of an approach with high efficiency to regulate BMSCs-induced M2 polarization, and strengthen the potential of cell therapeutics to enhance the reversal of behavioral deficits caused by ischemic stroke.