Macrophage AXL receptor tyrosine kinase inflames the heart after reperfused myocardial infarction.

Tyro3, AXL, and MerTK (TAM) receptors are activated in macrophages in response to tissue injury and as such have been proposed as therapeutic targets to promote inflammation resolution during sterile wound healing, including myocardial infarction. Although the role of MerTK in cardioprotection is well characterized, the unique role of the other structurally similar TAMs, and particularly AXL, in clinically relevant models of myocardial ischemia/reperfusion infarction (IRI) is comparatively unknown. Utilizing complementary approaches, validated by flow cytometric analysis of human and murine macrophage subsets and conditional genetic loss and gain of function, we uncover a maladaptive role for myeloid AXL during IRI in the heart. Cross signaling between AXL and TLR4 in cardiac macrophages directed a switch to glycolytic metabolism and secretion of proinflammatory IL-1ß, leading to increased intramyocardial inflammation, adverse ventricular remodeling, and impaired contractile function. AXL functioned independently of cardioprotective MerTK to reduce the efficacy of cardiac repair, but like MerTK, was proteolytically cleaved. Administration of a selective small molecule AXL inhibitor alone improved cardiac healing, which was further enhanced in combination with blockade of MerTK cleavage. These data support further exploration of macrophage TAM receptors as therapeutic targets for myocardial infarction.

Embryonic Microglia Interact with Hypothalamic Radial Glia during Development and Upregulate the TAM Receptors MERTK and AXL following an Insult.

Despite a growing appreciation for microglial influences on the developing brain, the responsiveness of microglia to insults during gestation remains less well characterized, especially in the embryo when microglia themselves are still maturing. Here, we asked if fetal microglia could coordinate an innate immune response to an exogenous insult. Using time-lapse imaging, we showed that hypothalamic microglia actively surveyed their environment by near-constant "touching" of radial glia projections. However, following an insult (i.e., IUE or AAV transduction), this seemingly passive touching became more intimate and long lasting, ultimately resulting in the retraction of radial glial projections and degeneration into small pieces. Mechanistically, the TAM receptors MERTK and AXL were upregulated in microglia following the insult, and Annexin V treatment inhibited radial glia breakage and engulfment by microglia. These data demonstrate a remarkable responsiveness of embryonic microglia to insults during gestation, a critical window for neurodevelopment.

M2C Polarization by Baicalin Enhances Efferocytosis via Upregulation of MERTK Receptor.

Baicalin is the main active ingredient primary isolated from the Chinese herb, Scutellaria baicalensis Georgi. Although baicalin can induce M2 macrophage polarization, we still do not know the subtype of macrophages polarized by baicalin. In this study, we characterized that murine bone marrow derived macrophages induced by M-CSF can be further polarized into M2C phenotype by baicalin. The signatures of M2C macrophages for mRNA expression like interferon regulatory factor 4 (IRF4), interleukin-10 (IL-10), MERTK and PTX3 were up-regulated. Moreover, we observed the concomitantly decreasing of tumor necrosis factor alpha (TNF- α ), interferon regulatory factor 5 (IRF5), IL-6. In contrast, M2 macrophages polarized by IL-4 increased gene transcript of arginase-1 (Arg-1) and surface marker of CD206 indicates that their identity as M2A rather than M2C subtypes. Interestingly, the phagocytosis as well as efferocytosis activity were significantly enhanced in M2C macrophage polarized by baicalin and these capacities were associated with the expression of MERTK receptor. Finally, we conclude that baicalin induced M2C macrophages polarization with both elevations of efferocytosis and anti-inflammatory activity.

Self-Organized Cerebral Organoids with Human-Specific Features Predict Effective Drugs to Combat Zika Virus Infection.

The human cerebral cortex possesses distinct structural and functional features that are not found in the lower species traditionally used to model brain development and disease. Accordingly, considerable attention has been placed on the development of methods to direct pluripotent stem cells to form human brain-like structures termed organoids. However, many organoid differentiation protocols are inefficient and display marked variability in their ability to recapitulate the three-dimensional architecture and course of neurogenesis in the developing human brain. Here, we describe optimized organoid culture methods that efficiently and reliably produce cortical and basal ganglia structures similar to those in the human fetal brain in vivo. Neurons within the organoids are functional and exhibit network-like activities. We further demonstrate the utility of this organoid system for modeling the teratogenic effects of Zika virus on the developing brain and identifying more susceptibility receptors and therapeutic compounds that can mitigate its destructive actions.