Emerging roles of IL-34 in health and disease

Tumor-associated macrophages: potential therapeutic strategies and future prospects in cancer

Macrophages are the most important phagocytes in vivo. However, the tumor microenvironment can affect the function and polarization of macrophages and form tumor-associated macrophages (TAMs). Usually, the abundance of TAMs in tumors is closely associated with poor prognosis. Preclinical studies have identified important pathways regulating the infiltration and polarization of TAMs during tumor progression. Furthermore, potential therapeutic strategies targeting TAMs in tumors have been studied, including inhibition of macrophage recruitment to tumors, functional repolarization of TAMs toward an antitumor phenotype, and other therapeutic strategies that elicit macrophage-mediated extracellular phagocytosis and intracellular destruction of cancer cells. Therefore, with the increasing impact of tumor immunotherapy, new antitumor strategies to target TAMs are now being discussed.

Conditional genetic deletion of CSF1 receptor in microglia ameliorates the physiopathology of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia in the world. Microglia are the innate immune cells of CNS; their proliferation, activation, and survival in pathologic and healthy brain have previously been shown to be highly dependent on CSF1R.

METHODS

Here, we investigate the impact of such receptor on AD etiology and microglia. We deleted CSF1R using Cre/Lox system; the knockout (KO) is restricted to microglia in the APP/PS1 mouse model. We induced the knockout at 3 months old, before plaque formation, and evaluated both 6- and 8-month-old groups of mice.

RESULTS

Our findings demonstrated that CSF1R KO did not impair microglial survival and proliferation at 6 and 8 months of age in APP cKO compared to their littermate-control groups APPSwe/PS1. We have also shown that cognitive decline is delayed in CSF1R-deleted mice. Ameliorations of AD etiology are associated with a decrease in plaque volume in the cortex and hippocampus area. A compensating system seems to take place following the knockout, since TREM2/β-Catenin and IL-34 expression are significantly increased. Such a compensatory mechanism may promote microglial survival and phagocytosis of Aβ in the brain.

CONCLUSIONS

Our results provide new insights on the role of CSF1R in microglia and how it interacts with the TREM2/β-Catenin and IL-34 system to clear Aβ and ameliorates the physiopathology of AD.

Effect of IL-34 on T helper 17 cell proliferation and IL-17 secretion by peripheral blood mononuclear cells from rheumatoid arthritis patients

Interleukin (IL)-34 is a new pro-inflammatory cytokine with elevated expression in rheumatoid arthritis (RA) patients. Our previous study showed that the frequency of T helper 17 (Th17) cells was also elevated in RA patients. Our study aimed to determine the effects of IL-34 on the proliferation, transcription factor expression and cytokine secretion of different subgroups of CD4 + T cells [Th1, Th2, Th17 and regulatory T (Treg) cells] in RA patients. Peripheral blood mononuclear cells (PBMCs) were isolated from the peripheral blood of 10 RA patients and stimulated with different concentrations of recombinant human (rh) IL-34 (0, 25, 50 and 100 ng/ml). Flow cytometry was used to determine the frequencies of the 4 subgroups of CD4 + T cells. Reverse transcription-PCR, western blotting and enzyme-linked immunosorbent assays were used to determine the mRNA and protein expression levels of transcription factors and cytokines. As a result, the frequency of Th17 cells was obviously increased under IL-34 stimulation. Moreover, the expression of the transcription factor retinoic acid-related orphan receptor (ROR-γt) and secretion of IL-17 by PBMCs were increased by stimulation with IL-34. However, there were no effects of IL-34 on transcription factors or cytokine secretion in Th1, Th2 and Treg cells. In conclusion, IL-34 can improve the proliferation of Th17 cells and expression of IL-17 in RA patients.

Microglial ontogeny, diversity and neurodevelopmental functions

Microglia are instrumental to the development, function, homeostasis and pathologies of the central nervous system. These brain-resident macrophages arise early in embryogenesis and seed the developing brain, where they differentiate in response to cues provided by their neural niche. Throughout life, microglia regulate the neural tissue through a variety of cellular functions influenced by intrinsic and extrinsic factors. Despite their importance, we are only starting to uncover how microglia colonize the brain, adopt distinct functional states during development and the long-term impact of early alteration of their functions. This review highlights the latest knowledge on the ontogeny of microglia, their developmental trajectory and emerging roles. Characterizing these processes will be critical for our understanding of both brain physiology and pathologies.