Macrophages: From Simple Phagocyte to an Integrative Regulatory Cell for Inflammation and Tissue Regeneration-A Review of the Literature

The understanding of macrophages and their pathophysiological role has dramatically changed within the last decades. Macrophages represent a very interesting cell type with regard to biomaterial-based tissue engineering and regeneration. In this context, macrophages play a crucial role in the biocompatibility and degradation of implanted biomaterials. Furthermore, a better understanding of the functionality of macrophages opens perspectives for potential guidance and modulation to turn inflammation into regeneration. Such knowledge may help to improve not only the biocompatibility of scaffold materials but also the integration, maturation, and preservation of scaffold-cell constructs or induce regeneration. Nowadays, macrophages are classified into two subpopulations, the classically activated macrophages (M1 macrophages) with pro-inflammatory properties and the alternatively activated macrophages (M2 macrophages) with anti-inflammatory properties. The present narrative review gives an overview of the different functions of macrophages and summarizes the recent state of knowledge regarding different types of macrophages and their functions, with special emphasis on tissue engineering and tissue regeneration.

VSIG4 overexpression alleviates acute kidney injury of mice via inhibition of M1-macrophages activation

Background

The infiltration and activation of M1-macrophages can promote renal tubular interstitial damage. The study aimed to investigate the effect of V-set and immunoglobulin domain containing 4 (VSIG4) on M1-macrophages activation and acute kidney injury (AKI) mice.

Methods

The M1-macrophage markers cluster of differentiation 86 (CD86) and inducible nitric oxide synthase (iNOS) were detected via flow cytometry. Cell viability and expression of inflammatory factors were analyzed through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), as well as quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA) assays. Moreover, HK-2 cells stimulated with lipopolysaccharide (LPS) and RAW264.7 cells overexpressing VSIG4 were co-cultured to analyze the effect of VSIG4 suppressing M1-macrophage activation on HK-2 cells via detecting cell proliferation and apoptosis levels. Furthermore, the pathological changes and iNOS expression of kidney tissue in VSIG4 knockout mice with renal ischemia-reperfusion injury (IRI) were detected by hematoxylin and eosin (H&E) and immunohistochemistry (IHC) staining.

Results

Overexpression of VSIG4 partially reversed the phenomenon of M1-macrophageactivation caused by LPS-upregulated CD86 and iNOS expression, reduced cell viability, and induced the expression levels of interleukin 1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-α (TNF-α) in RAW264.7. In addition, RAW264.7 cells overexpressing VSIG4 could also alleviate the low proliferation and high apoptotic level of HK-2 cells stimulated with LPS. After VSIG4 knockout, the kidney tissue of AKI mice showed obvious lesions and iNOS expression, indicating that VSIG4 knockout promoted the infiltration of M1-macrophages in the damaged kidney tissue and accelerated kidney tissue lesions.

Conclusions

Overexpression of VSIG4 might alleviate the lesions of kidney tissue in AKI mice via inhibition of the secretion of inflammatory factors in M1-macrophages.