Macrophage activation and migration in the microenvironment of spinal cord injury

• Main Authors: Chuan-Wen Chiu, 邱詮文
• Other Authors: Henrich Cheng
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/6jjc26

博士 === 國立陽明大學 === 藥理學研究所 === 105 === Spinal cord injury (SCI) can lead to severe disability, sensory disorder, neurological deficits and even death. Patients with SCI can be seriously disabling and lose their living ability, thus leading to financial problems to the family and country. Following SCI, the damaged tissue elicits chemokines and attracts immune cells, predominantly macrophages, to the injured sites. As we know, post-injury central nervous system (CNS) wound healing occurs via the balance of two major populations of macrophages: the classically activated macrophages (M1) and the alternatively activated macrophages (M2). M1 macrophages leading to further devastating neuronal cell death and the loss of neurons, oligodendrocytes and myelin (Secondary damage). In contrast, M2 macrophages promote angiogenesis, tissue repair, and axonal growth during acute inflammation. Our previous study demonstrated that a repair model of a peripheral nerve graft and acidic fibroblast growth factor (FGF-1) increased the numbers of M2 macrophages recruitment into the grafted area and improved functional recovery. Therefore, we hypothesized that macrophage activation and migration in the microenvironment of SCI would determine whether infiltrating macrophages aggravate secondary injury or promote repair. Decoy receptor 3 (DcR3) is a pleiotropic immunomodulator capable of inducing macrophage differentiation into the M2 phenotype and enhancing angiogenesis. Hence, the aim in the first part of this dissertation, we asked whether the administration of recombinant DcR3 (DcR3.Fc) is able to increase population of M2 macrophage, promote tissue repair and the recovery after contusive SCI. Moreover, because of migration in macrophage is matrix metalloproteinases (MMPs)-dependent. In the second part of this dissertation, we used general MMPs inhibitor (GM6001) to block the migration of macrophages in our repair model. To discuss the potential dilemmas of MMPs inhibitor which to applied in the M2-dominated microenvironment at the lesion site of repaired rat. In the first study, the results have shown that DcR3.Fc can modulate the macrophage response in SCI to facilitate tissue sparing and functional recovery. Compared with the control group, DcR3.Fc-treated rats had increased vascularization at the injury epicenter along with higher levels of interleukin (IL)-4 and IL-10, and lower level of IL-1β. Moreover, higher levels of arginase I (Arg I) and CD206 (M2 macrophage markers), and RECA-1 (endothelial marker) were observed in the epicenter by immunofluorescence staining on DcR3.Fc-treated rats. Thus, DcR3.Fc may become a promising therapeutic agent for SCI patients in the future. On top of that, in present of the second part, we demonstrated that levels of MMP-9 were upregulated in the graft area of repaired rats compared to transected rats. Furthermore, the MMP-2 and MMP-9 were expressed by astrocytes and macrophages, respectively. Local application of MMPs inhibitor resulted in a reduction of M2/M1 ratio, which is demonstrated by differential levels of Arg I and inducible nitric oxide synthase (iNOS), while as impairing of brain-derived neurotrophin (BDNF) expression and functional recovery after operation. These results suggest that MMP-9 is one of the possible factors for M2 macrophage migration to graft, thereby creating a more permissive environment for functional recovery in our repaired model. Several strategies, including cell therapy, molecular therapy, and combinatorial treatment, have been developed in SCI animal models. However, only a few approaches can be applied in clinical trials. In this dissertation, we may be able to provide an optimal therapeutic agent of DcR3.Fc in the SCI and advise using MMPs inhibitor should be considered with caution if the co-administered treatment involved M2 macrophage recruitment. Keywords: Spinal cord injury, DcR3, Classically activated macrophage (M1), Alternatively activated macrophage (M2), MMP