Identification of a unique TGF-ß-dependent molecular and functional signature in microglia.

Microglia are myeloid cells of the CNS that participate both in normal CNS function and in disease. We investigated the molecular signature of microglia and identified 239 genes and 8 microRNAs that were uniquely or highly expressed in microglia versus myeloid and other immune cells. Of the 239 genes, 106 were enriched in microglia as compared with astrocytes, oligodendrocytes and neurons. This microglia signature was not observed in microglial lines or in monocytes recruited to the CNS, and was also observed in human microglia. We found that TGF-ß was required for the in vitro development of microglia that express the microglial molecular signature characteristic of adult microglia and that microglia were absent in the CNS of TGF-ß1-deficient mice. Our results identify a unique microglial signature that is dependent on TGF-ß signaling and provide insights into microglial biology and the possibility of targeting microglia for the treatment of CNS disease.

Modulating inflammatory monocytes with a unique microRNA gene signature ameliorates murine ALS.

Amyotrophic lateral sclerosis (ALS) is a progressive disease associated with neuronal cell death that is thought to involve aberrant immune responses. Here we investigated the role of innate immunity in a mouse model of ALS. We found that inflammatory monocytes were activated and that their progressive recruitment to the spinal cord, but not brain, correlated with neuronal loss. We also found a decrease in resident microglia in the spinal cord with disease progression. Prior to disease onset, splenic Ly6Chi monocytes expressed a polarized macrophage phenotype (M1 signature), which included increased levels of chemokine receptor CCR2. As disease onset neared, microglia expressed increased CCL2 and other chemotaxis-associated molecules, which led to the recruitment of monocytes to the CNS by spinal cord-derived microglia. Treatment with anti-Ly6C mAb modulated the Ly6Chi monocyte cytokine profile, reduced monocyte recruitment to the spinal cord, diminished neuronal loss, and extended survival. In humans with ALS, the analogous monocytes (CD14+CD16-) exhibited an ALS-specific microRNA inflammatory signature similar to that observed in the ALS mouse model, linking the animal model and the human disease. Thus, the profile of monocytes in ALS patients may serve as a biomarker for disease stage or progression. Our results suggest that recruitment of inflammatory monocytes plays an important role in disease progression and that modulation of these cells is a potential therapeutic approach.

Activation of the aryl hydrocarbon receptor induces human type 1 regulatory T cell-like and Foxp3(+) regulatory T cells.

The aryl hydrocarbon receptor (AhR) participates in the differentiation of mouse regulatory T cells (T(reg) cells) and interleukin 17 (IL-17)-producing helper T cells (T(H)17 cells), but its role in human T cell differentiation is unknown. We investigated the role of AhR in the differentiation of human induced T(reg) cells (iT(reg) cells). We found that AhR activation promoted the differentiation of CD4(+)Foxp3(-) T cells, which produce IL-10 and control responder T cells through granzyme B. However, activation of AhR in the presence of transforming growth factor-beta1 induced Foxp3(+) iT(reg) cells, which suppress responder T cells through the ectonucleoside triphosphate diphosphohydrolase CD39. The induction of functional Foxp3(+) iT(reg) cells required coordinated action of the transcriptional regulators Smad1 and Aiolos. Thus, AhR is a potential target through which functional iT(reg) cells could be induced in human autoimmune disorders.