Primary Human M2 Macrophage Subtypes Are Distinguishable by Aqueous Metabolite Profiles

The complexity of macrophage (MΦ) plasticity and polarization states, which include classically activated pro-inflammatory (M1) and alternatively activated anti-inflammatory (M2) MΦ phenotypes, is becoming increasingly appreciated. Within the M2 MΦ polarization state, M2a, M2b, M2c, and M2d MΦ subcategories have been defined based on their expression of specific cell surface receptors, secreted cytokines, and specialized immune effector functions. The importance of immunometabolic networks in mediating the function and regulation of MΦ immune responses is also being increasingly recognized, although the exact mechanisms and extent of metabolic modulation of MΦ subtype phenotypes and functions remain incompletely understood. In this study, proton (1H) nuclear magnetic resonance (NMR) metabolomics was employed to determine the polar metabolomes of M2 MΦ subtypes and to investigate the relationship between aqueous metabolite profiles and M2 MΦ functional phenotypes. Results from this study demonstrate that M2a MΦs are most distinct from M2b, M2c, and M2d MΦ subtypes, and that M2b MΦs display several metabolic traits associated with an M1-like MΦ phenotype. The significance of metabolome differences for metabolites implicated in glycolysis, the tricarboxylic acid (TCA) cycle, phospholipid metabolism, and creatine-phosphocreatine cycling is discussed. Altogether, this study provides biochemical insights into the role of metabolism in mediating the specialized effector functions of distinct M2 MΦ subtypes and supports the concept of a continuum of macrophage activation states rather than two well-separated and functionally distinct M1/M2 MΦ classes, as originally proposed within a classical M1/M2 MΦ framework.

The effects of the M2a macrophage-induced axonal regeneration of neurons by arginase 1

BACKGROUND

Spinal cord injury (SCI) is a challenge worldwide, but there are no effective treatments or therapeutic methods in the clinic. Recent studies have shown that type I arginase (Arginase1, Arg1) is closely associated with the treatment of SCI. The classical treatment for SCI involves filling the local area of SCI with activated M2a macrophages to allow the repair and regeneration of some synapses, but the specific mechanism of action of Arg1 is not clear.

METHOD

In the present study, we first induced the polarization of RAW264.7 macrophages to M2a-type cells using IL-4 and constructed an Arg1 knockout cell line through the use of shRNA; we used these cells to treat a rat model of SCI. Finally, the present study explored the mechanism and pathway by which Arginase 1 regulates spinal repair by immunoblotting and immunohistochemistry.

RESULT

Suspended M2a (Arg1-/+) macrophages were transplanted into the injury site in a rat model of contusion SCI. Compared with the model group and the shArg1 group, the shScramble (shSc) group exhibited higher Basso, Beattie, Bresnahan motor function scores, more compact structures and more Nissl bodies. Immunohistochemical results showed that the shSc group expressed higher levels of NeuN (a neuronal marker) and tau (an axonal marker), as well as the up-regulation of Cdc42, N-WASP, Arp2/3 and tau, as determined by Western blot.

CONCLUSION

The study found that the polarization of M2a macrophages promoted the expression of Arginase 1, which restored axonal regeneration, promoted axonal regeneration, and promoted the structural and functional recovery of the contused spinal cord.

Dynamic macrophage polarization-specific miRNA patterns reveal increased soluble VEGF receptor 1 by miR-125a-5p inhibition

Dynamic, epigenetic mechanisms can regulate macrophage phenotypes following exposure to different stimulating conditions and environments. However, temporal patterns of microRNAs (miRNAs or miRs) across multiple macrophage polarization phenotypes have not been defined. We determined miRNA expression in bone marrow-derived murine macrophages over multiple time points (0.5, 1, 3, 24 h) following exposure to cytokines and/or LPS. We hypothesized that dynamic changes in miRNAs regulate macrophage phenotypes. Changes in macrophage polarization markers were detected as early as 0.5 and as late as 24 h; however, robust responses for most markers occurred within 3 h. In parallel, many polarization-specific miRNAs were also changed by 3 h and expressed divergent patterns between M1 and M2a conditions, with increased expression in M1 (miR-155, 199a-3p, 214-3p, 455-3p, and 125a) or M2a (miR-511 and 449a). Specifically, miR-125a-5p exhibited divergent patterns: increased at 12-24 h in M1 macrophages and decreasing trend in M2a. VEGF in the culture media of macrophages was dependent upon the polarization state, with greatly diminished VEGF in M2a compared with M1 macrophage culture media despite similar VEGF in cell lysates. Inhibition of miR-125a-5p in media-only controls (MO) and M1 macrophages greatly increased expression and secretion of soluble VEGF receptor-1 (sVEGFR1) leading to diminished VEGF in the culture media, partially converting MO and M1 into an M2a phenotype. Thus, the divergent expression patterns of polarization-specific miRNAs led to the identification and demonstrated the regulation of a specific macrophage polarization phenotype, sVEGFR1 by inhibition of miR-125a-5p.

IL-4 signaling drives a unique arginase+/IL-1β+ microglia phenotype and recruits macrophages to the inflammatory CNS: consequences of age-related deficits in IL-4Rα after traumatic spinal cord injury

Alternative activation of microglia/macrophages (M2a) by interleukin (IL)-4 is purported to support intrinsic growth and repair processes after CNS injury. Nonetheless, alternative activation of microglia is poorly understood in vivo, particularly in the context of inflammation, injury, and aging. Here, we show that aged mice (18-19 months) had reduced functional recovery after spinal cord injury (SCI) associated with impaired induction of IL-4 receptor α (IL-4Rα) on microglia. The failure to successfully promote an IL-4/IL-4Rα response in aged mice resulted in attenuated arginase (M2a associated), IL-1β, and chemokine ligand 2 (CCL2) expression, and diminished recruitment of IL-4Rα(+) macrophages to the injured spinal cord. Furthermore, the link between reduced IL-4Rα expression and reduced arginase, IL-1β, and CCL2 expression was confirmed using adult IL-4Rα knock-out (IL-4Rα(KO)) mice. To better understand IL-4Rα-mediated regulation of active microglia, a series of studies was completed in mice that were peripherally injected with lipopolysaccharide and later provided IL-4 by intracerebroventricular infusion. These immune-based studies demonstrate that inflammatory-induced IL-4Rα upregulation on microglia was required for the induction of arginase by IL-4. In addition, IL-4-mediated reprogramming of active microglia enhanced neurite growth ex vivo and increased inflammatory gene expression (i.e., IL-1β and CCL2) and the corresponding recruitment of CCR2(+)/IL-4Rα(+)/arginase(+) myeloid cells in vivo. IL-4 reprogrammed active microglia to a unique and previously unreported phenotype (arginase(+)/IL-1β(+)) that augmented neurite growth and enhanced recruitment of peripheral IL-4Rα(+) myeloid cells to the CNS. Moreover, this key signaling cascade was impaired with age corresponding with reduced functional recovery after SCI.

Phylogenetic analysis and positive-selection site detecting of vascular endothelial growth factor family in vertebrates

Vascular endothelial growth factor (VEGF), known to play an important role in vascular homeostasis, vascular integrity and angiogenesis, is little known about the evolutionary relationship of its five members especially the role of gene duplication and natural selection in the evolution of the VEGF family. In this study, seventy-five full-length cDNA sequences from 33 vertebrate species were extracted from the NCBI's GenBank, UniProt protein database and the Ensembl database. By phylogenetic analyses, we investigated the origin, conservation, and evolution of the VEGFs. Five VEGF family members in vertebrates might be formed by gene duplication. The inferred evolutionary transitions that separate members which belong to different gene clusters correlated with changes in functional properties. Selection analysis and protein structure analysis were combined to explain the relationship of the site-specific evolution in the vertebrate VEGF family. Eleven positive selection sites, one transmembrane region and the active sites were detected in this process.

Macrophage phenotypes during tissue repair

Mp are crucial for tissue repair and regeneration but can also contribute to tissue damage and fibrosis. Mp can adopt a variety of functional phenotypes in response to different stimuli; two of the best-characterized in vitro phenotypes are a proinflammatory "M1" phenotype, produced by exposure to IFN-γ and TNF-α, and an anti-inflammatory "M2a" phenotype, produced by IL-4 or IL-13. M2a Mp are frequently termed "wound healing" Mp, as they express factors that are important for tissue repair. This review will summarize current knowledge of Mp phenotypes during tissue repair and will argue that these in vivo Mp populations are heterogeneous and temporally regulated and do not conform to existing, in vitro-defined M1 or M2 phenotypes. Mp during the early stages of tissue repair exhibit a more proinflammatory phenotype than their later counterparts, which in turn may exhibit some M2a-associated characteristics. However, phenotypic markers that appear to be coregulated in cultured Mp can be expressed independently of each other in vivo. Additionally, M1- and M2-associated markers may be expressed simultaneously by actual tissue-repair Mp. Improved understanding of Mp phenotypes and their regulation may assist in generation of novel therapies based on manipulating Mp function to improve healing.