Microglia Polarization with M1/M2 Phenotype Changes in rd1 Mouse Model of Retinal Degeneration

Abstract

Microglia activation is recognized as the hallmark of neuroinflammation. However, the activation profile and phenotype changes of microglia during the process of retinal degeneration are poorly understood. This study aimed to elucidate the time-spatial pattern of microglia distribution and characterize the polarized phenotype of activated microglia during retinal neuroinflammation and degeneration in rd1 (Pde6βrd1/rd1) mice, the classic model of inherited retinal degeneration. Retinae of rd1 mice at different postnatal days (P7, P14, P21, P28, P56, and P180) were prepared for further analysis. We found most CD11b+ or IBA1+ microglia expressed Ki-67 and CD68 in rd1 mice and these cells migrated toward the layer of degenerative photoreceptors at the rapid rods degeneration phase from P14 to P28. These microglia exhibited typical ameboid activated shape with round bodies and scarce dendrites, while at late phase at P180, they displayed resting ramified morphology with elongated dendrites. Flow cytometry revealed that the percentage of CD86+CD206- M1 microglia increased markedly in rd1 retinae, however, no significant change was observed in CD206+CD86- M2 microglia. Interestingly, CD86+CD206+ microglia, an intermediate state between the two extremes of M1 and M2, increased markedly at the rapid rods degeneration phase. The immunofluorescence images revealed that microglia in rd1 mice highly expressed M1 markers including CD16/32, CD86, and CD40. In addition, increased expression of pro-inflammatory cytokines (TNF-α, IL-6, and CCL2) was observed in rd1 mice. Our findings unfolded a panorama for the first time that microglia conducted distinctive behaviors with the progression of retinal degeneration in rd1 mice. Microglia is activated and particularly polarized to a pro-inflammatory M1 phenotype at the rapid rods degenerative phase, suggesting that the involvement of M1 microglia in the retinal neuroinflammation and degeneration. Most microglia adopted an intermediate polarization “M1½” state in rd1, revealing that microglia orchestrated a complicated continuous spectrum in degenerative retina.

Evaluation of Microglia/Macrophage Cells from Rat Striatum and Prefrontal Cortex Reveals Differential Expression of Inflammatory-Related mRNA after Methamphetamine

“…In broad terms, M1-polarization is characterized as activated microglia which produce and release inflammatory mediators themselves, whereas, M2-polarization is associated with activated microglia producing and releasing mediators which act in a neuroprotective role. Table 8 compares RNAseq data from our 2 h post-METH STR and PFC to 47 genes cited in literature reviews as indicating M1 or M2 polarization of microglia [35][36][37][38][39]. Of these 47 genes, we found 12 genes were significantly changed by binge METH in the same direction as reported in the literature (shaded in green).…”

“…These findings add to a growing body of literature that microglial activation can be further differentiated beyond M1 and M2 that depend on the type of insult [44,45]. More specifically, microglial activation states also differ in rodent models of aging [34], retinal degeneration [38], ischemia [37,46], Alzheimer's disease [47], Parkinson's disease [48,49], and binge alcohol consumption [39].…”

Evaluation of Chitotriosidase and CC-Chemokine Ligand 18 as Biomarkers of Microglia Activation in Amyotrophic Lateral Sclerosis

“…The macrophage/microglia polarization describes the capacity of differentiated macrophages to respond to external stimuli by changing their phenotype and functions. The M1-like microglia phenotype produces proinflammatory cytokines (TNF-alpha, IL-1beta, IL-6, IL-12 and an array of cytotoxic molecules) [46,47]. We could assume an M2-like microglia phenotype that would produce, just like macrophages, anti-inflammatory cytokines (IL-10, IL-4, TGF-beta, other neurotrophic factors, and chemokines CCL17 and CCL18) [23,42,[48][49][50].…”

Modulators of microglia activation and polarization in ischemic stroke (Review)

“…in addition, c-c motif chemokine ligand 2 (ccl2) generated by microglia was observed to recruit cd8 + γδ T cells to the ischemic brain, which was identified to be the primary factor aggravating brain infarction (32,33). in fact, besides ischemic stroke, M1 microglia activation occurs in multiple other neurological diseases; for example, in an RD1 mouse model of retinal degeneration, flow cytometry analysis revealed that the percentage of T-lymphocyte activation antigen cd86 (cd86) + M1 microglia was markedly increased in the rapid degeneration phase (34); paraquat stimulation was revealed to activate M1 microglia, which subsequently activated the toll-like receptor-4 (Tlr4)-mediated nF-κB signaling pathway and resulted in the release of proinflammatory cytokines (35); and the number of low affinity immunoglobulin gamma Fc region receptor iii-a/b (cd16/32) + M1 microglia was significantly increased in the brains of subarachnoid hemorrhage model mice through the activation of the myeloid differentiation primary response protein Myd88 (Myd88)/mitogen-activated protein kinase pathway, whereas decreasing the percentage of M1 microglia significantly improved the neurological deficits (36). other results from the literature have indicated that M1 microglia activation can also aggravate brain damage in other types of neurological disease (34)(35)(36).…”