Targeting miR‐155 restores abnormal microglia and attenuates disease in SOD1 mice

Abstract

OBJECTIVE To investigate miR-155 in the SOD1 mouse model and human sporadic and familial amyotrophic lateral sclerosis (ALS). METHODS Nanostring microRNA, microglia and immune gene profiles, protein mass spectrometry and RNA-seq analyses were measured in spinal cord microglia, splenic monocytes and spinal cord tissue from SOD1 mice and in spinal cord tissue of familial and sporadic ALS. miR-155 was targeted by genetic ablation or by peripheral or centrally administered anti-miR-155 inhibitor in SOD1 mice. RESULTS In SOD1 mice we found loss of the molecular signature that characterizes microglia and increased expression of miR-155. There was loss of the microglial molecules P2ry12, Tmem119, Olfml3, transcription factors Egr1, Atf3, Jun, Fos, Mafb and the upstream regulators Csf1r, Tgfb1 and Tgfbr1 which are essential for microglial survival. Microglia biological functions were suppressed including phagocytosis. Genetic ablation of miR-155 increased survival in SOD1 mice by 51d in females and 27d in males and restored the abnormal microglia and monocyte molecular signatures. Disease severity in SOD1 males was associated with early upregulation of inflammatory genes including Apoe in microglia. Treatment of adult microglia with APOE suppressed the M0-unique microglia signature and induced a M1-like phenotype. miR-155 expression was increased in the spinal cord of both familial and sporadic ALS. Dysregulated proteins that we identified in human ALS spinal cord were restored in SOD1G93A/miR-155−/− mice. Intraventricular anti-miR-155 treatment derepressed microglial miR-155 targeted genes and peripheral anti-miR-155 treatment prolonged survival. INERPRETATION We found overexpression of miR-155 in the SOD1 mouse and in both sporadic and familial human ALS. Targeting miR-155 in SOD1 mice restores dysfunctional microglia and ameliorates disease. These findings identify miR-155 as a therapeutic target for the treatment of ALS.

Serotonin 2B receptor slows disease progression and prevents degeneration of spinal cord mononuclear phagocytes in amyotrophic lateral sclerosis

“…Such loss of homeostatic microglial gene expression in whole tissue could be due to cell loss, leading to decreased proportion of microglial mRNAs. Alternatively, disease progression could also affect microglial phenotype, and a recent study performed on isolated microglia of mutant SOD1 mice observed that mutant SOD1 microglia lost their typical expression patterns with disease progression [7]. However, our in vitro experiments provide an initial proof of concept that microglial survival could be influenced by serotonergic stimulation of the 5-HT 2B R. Further work is required to determine the relative contributions of microglial cell death and altered microglial phenotypes in the observed degenerative phenotype in vivo as well as the importance of monocyte degeneration.…”

“…5c), suggesting that the loss of Htr2b was associated with degeneration of mononuclear phagocytes in end stage SOD1(G86R) mice. To determine whether this degeneration of mononuclear phagocytes affected microglia and/or monocytes, we measured expression levels of genes known to be part of the homeostatic microglial signature [12,8,9,7], in particular Cx3cr1, Hexb, Tmem119, P2ry12, Olflm3 and SiglecH. All these genes displayed lower expression in SOD1(G86R) mice lacking the Htr2b gene than in SOD1(G86R) mice with the Htr2b gene (Fig.…”

“…Recently, genome-wide characterization of microglial and monocyte expression patterns led to the identification of a molecular signature of homeostatic microglia. Specifically, microglia express genes not expressed in circulating monocytes or other resident tissue macrophages such as P2ry12, Hexb, Olfml3, SiglecH, Tgfbr1 or Tmem119 [8,48,31,12,7]. Contrastingly, monocytes express surface markers not present on microglia, such as Ly6c1 [9].…”

“…Contrastingly, monocytes express surface markers not present on microglia, such as Ly6c1 [9]. Importantly, microglia lose the expression of their homeostatic signature during disease progression [12,7], and develop unique expression patterns during experimental ALS distinct from inflammation-induced alteration [12,7]. This loss of typical microglial expression patterns could be directly correlated with degeneration of CNS macrophages, documented in different neurodegenerative diseases [58,57,69] including a transgenic model of ALS [24,58].…”

RNA-targeted Therapeutics for ALS

“…An ASO generated against miR-155 was then shown to prolong survival (by 7%) and prolong disease duration (by 38%) when injected intraventricularly after disease onset [41]. Similar slowing of disease in SOD1G93A mice and prolongation of survival (by 8%) was achieved by a second group inhibiting miR-155 [42].…”