Distinct spatial distribution of microglia and macrophages following mesenchymal stem cell implantation in mouse brain

Abstract

Although implantation of cellular material in the central nervous system (CNS) is a key direction in CNS regenerative medicine, this approach is currently limited by the occurrence of strong endogenous immune cell responses. In a model of mesenchymal stem cell (MSC) grafting in the CNS of immune-competent mice, we previously described that MSC grafts become highly surrounded and invaded by Iba1 þ myeloid cells (microglia and/or macrophages). Here, following grafting of blue fluorescent protein (BFP)-expressing MSC in the CNS of CX 3 CR1 þ / À and CX 3 CR1 À/ À mice, our results indicate: (1) that the observed inflammatory response is independent of the fractalkine signalling axis, and (2) that a significant spatial distribution of Iba1 þ inflammatory cells occurs, in which Iba1 þ CX 3 CR1 þ myeloid cells mainly surround the MSC graft and Iba1 þ CX 3 CR1 À myeloid cells mainly invade the graft at 10 days post transplantation. Although Iba1 þ CX 3 CR1 þ myeloid cells are considered to be of resident microglial origin, Iba1 þ CX 3 CR1 À myeloid cells are most likely of peripheral monocyte/macrophage origin. In order to confirm the latter, we performed MSC-BFP grafting experiments in the CNS of eGFP þ bone marrow chimeric C57BL/6 mice. Analysis of MSC-BFP grafts in the CNS of these mice confirmed our observation that peripheral monocytes/macrophages invade the MSC graft and that resident microglia surround the MSC graft site. Furthermore, analysis of major histocompatibility complex class II (MHCII) expression revealed that mainly macrophages, but not microglia, express this M1 pro-inflammatory marker in the context of MSC grafting in the CNS. These results again highlight the complexity of cell implantation immunology in the CNS.

Dynamic Modulation of Microglia/Macrophage Polarization by miR-124 after Focal Cerebral Ischemia

“…Interestingly, however, the early injection of negative control of miR at day 2 after ischemia only gave rise to a smaller M1 marker expression by Iba-1 + cells in comparison to the stroke only group. In support of our observation, Le Blon and colleagues observed fewer MHCII + expressions by Iba-1 + cells, as M1 associated marker, in sham implanted group in a mouse model of mesenchymal stem cell implantation (Le Blon et al 2014). …”

Intracerebral transplantation of interleukin 13-producing mesenchymal stem cells limits microgliosis, oligodendrocyte loss and demyelination in the cuprizone mouse model

“…In this study, we used a previously established and characterised C57BL/6 mouse BM-derived MSC line (further named as parental MSC) [20] and a derivative thereof, genetically engineered to express the blue fluorescent protein (further named as blue fluorescent protein (BFP)-MSC) [13]. For expansion, both MSC lines were cultured in standard cell culture plasticware (well plates and/or culture flasks) in ‘complete expansion medium’ (CEM) [21] consisting of Iscove’s modified Dulbecco’s medium (IMDM; Lonza) supplemented with 8% fetal bovine serum (FBS; Invitrogen), 8% horse serum (HS; Invitrogen), 200U/ml + 100 μg/ml penicillin/streptomycin (Invitrogen) and 1 μg/ml amphotericin B (Invitrogen).…”

“…MSC cultures were split 1:5 twice a week using 0.05% trypsin-EDTA (Invitrogen) for cell detachment. Both the parental MSC line and the BFP-MSC line were transduced with the pCHMWS-IL13-IRES-Pac LVv, according to previously optimised procedures [13, 21]. Following puromycin selection, the resulting engineered MSC lines were further named as IL13-MSC and IL13/BFP-MSC.…”

“…In order to discriminate between microglia and macrophages, eGFP + BM chimaeric mice were generated as previously described [13]. Briefly, wild-type C57BL/6 mice received 10Gy total body irradiation using an XRAD320 small animal irradiation device (Precision X-Ray).…”

Anti-inflammatory effect of stem cells against spinal cord injury via regulating macrophage polarization

“…74,75 Recently, it has become clear that MSCs also regulate the function and activation of macrophages. [76][77][78][79] There is a large body of evidence demonstrating that the effects of MSCs on macrophages are critical for inflammatory response and tissue repair after SCI. [80][81][82][83][84] Nakajima et al observed that BM-MSCs altered macrophages into anti-inflammatory M2 and beneficially modulated the immune system.…”