Probes for CX3CL1

With the rise of e-cigarette use, teen nicotine exposure is becoming more widespread. Findings from clinical and preclinical studies show that the adolescent brain is particularly sensitive to nicotine. Animal studies have demonstrated that adolescent nicotine exposure increases reinforcement for cocaine and other drugs. However, the mechanisms that underlie these behaviors are poorly understood. Here, we report reactive microglia are critical regulators of nicotine-induced increases in adolescent cocaine self-administration. Nicotine has dichotomous, age-dependent effects on microglial morphology and immune transcript profiles. A multistep signaling mechanism involving D2 receptors and CX3CL1 mediates nicotine-induced increases in cocaine self-administration and microglial activation. Moreover, nicotine depletes presynaptic markers in a manner that is microglia-, D2- and CX3CL1-dependent. Taken together, we demonstrate that adolescent microglia are uniquely susceptible to perturbations by nicotine, necessary for nicotine-induced increases in cocaine-seeking, and that D2 receptors and CX3CL1 play a mechanistic role in these phenomena

Maturation of the definitive adrenal cortex occurs between 3 and 6 weeks post-partum and involves onset of CYP11B2 expression and establishment of the laminin-encased 3D structure of glomeruli that contain rosettes of 10 to 15 zona glomerulosa (zG) cells that work in coordination to produce optimal amounts of aldosterone. Although this process is dependent on canonical WNT/b-catenin signaling, cellular sources of WNT ligands remain elusive and the mechanisms involved in the extensive extra-cellular matrix remodeling associated with rosette/glomeruli morphogenesis are unknown. Beyond their role in innate immunity, macrophages are involved in extra-cellular matrix remodeling under a wide variety of pathophysiological conditions and have the capacity to produce WNT ligands. This, together with the presence of macrophages within the zG cells, strongly suggest that macrophages may play a role in zG morphogenesis and differentiation. Supporting this idea, a recent publication has shown that intra-tissular aldosterone concentration was reduced in the absence of macrophages under stress conditions. However, whether macrophages play a direct role in controlling aldosterone secretion or an indirect role by remodelling the postnatal zG is unknown. The presence of tissue resident macrophages in a specific zone is dependent on the production of trophic factors such as IL34, CSF1, CSF2 or CX3CL1 by nearby, tissue resident ‘niche’ cells. In return, macrophages are thought to provide positive ‘feedback’ signals to their niche, generating mutually beneficial circuits between the niche and its macrophages. To gain insight into the role of macrophages in zG morphogenesis and homeostasis, we used single cell sequencing and RNAscope analyses to show expression of CX3CL1 in the zG and of CX3CR1 in macrophages. Interestingly, CX3CL1 expression in the zG was downstream of WNT signalling, suggesting existence of a bi-directional interaction between macrophages and zG. To further study the role of macrophages during the maturation of the zG, we pharmacologically depleted macrophages by the small molecule inhibitor Pexidartinib at different time points between 3- and 12-weeks post-partum, when maturation of the zG occurs. Short-term depletion of macrophages resulted in a more disorganized and elongated zG, suggesting a delay in maturation. However, long-term depletion of macrophages resulted in exacerbated maturation of the rosettes, suggesting that the short-term zG defect was followed by establishment of a compensatory mechanism to allow formation of rosettes even in the absence of macrophages. Whether these perturbations of the zG are correlated with an altered production of aldosterone is still under study.

Valvular inflammation triggered by hyperlipidemia has been considered as an important initial process of aortic valve disease; however, cellular and molecular evidence remains unclear. Here, we assess the relationship between plasma lipids and valvular inflammation, and identify association of low-density lipoprotein with increased valvular lipid and macrophage accumulation. Single-cell RNA sequencing analysis reveals the cellular heterogeneity of leukocytes, valvular interstitial cells, and valvular endothelial cells, and their phenotypic changes during hyperlipidemia leading to recruitment of monocyte-derived MHC-IIhi macrophages. Interestingly, we find activated PPARγ pathway in Cd36+ valvular endothelial cells increased in hyperlipidemic mice, and the conservation of PPARγ activation in non-calcified human aortic valves. While the PPARγ inhibition promotes inflammation, PPARγ activation using pioglitazone reduces valvular inflammation in hyperlipidemic mice. These results show that low-density lipoprotein is the main lipoprotein accumulated in the aortic valve during hyperlipidemia, leading to early-stage aortic valve disease, and PPARγ activation protects the aortic valve against inflammation.

Emerging insights from numerous laboratories have revealed important roles for non-neoplastic cells in the development and progression of brain tumors. One of these non-neoplastic cellular constituents, glioma-associated microglia (GAM), represents a unique population of brain monocytes within the tumor microenvironment that have been reported to both promote and inhibit glioma proliferation. To elucidate the role of GAM in the setting of low-grade glioma (LGG), we leveraged RNA sequencing meta-analysis, genetically engineered mouse strains, and human biospecimens. Publically available disease-associated microglia (DAM) RNA-seq datasets were used, followed by immunohistochemistry and RNAScope validation. CD11a-deficient mouse microglia were used for in vitro functional studies, while LGG growth in mice was assessed using anti-CD11a neutralizing antibody treatment of Nf1 optic glioma mice in vivo. We identified Itgal/CD11a enrichment in GAM relative to other DAM populations, which was confirmed in several independently generated murine models of Neurofibromatosis type 1 (Nf1) optic glioma. Moreover, ITGAL/CD11A expression was similarly increased in human LGG (pilocytic astrocytoma) specimens from several different datasets, specifically in microglia from these tumors. Using CD11a-knockout mice, CD11a expression was shown to be critical for murine microglia CX3CL1 receptor (Cx3cr1) expression and CX3CL1-directed motility, as well as glioma mitogen (Ccl5) production. Consistent with an instructive role for CD11a + microglia in stromal control of LGG growth, antibody-mediated CD11a inhibition reduced mouse Nf1 LGG growth in vivo. Collectively, these findings establish ITGAL/CD11A as a critical microglia regulator of LGG biology relevant to future stroma-targeted brain tumor treatment strategies.