Effect of hypoxia on function and metabolism of the alveolar macrophages

Macrophage transcriptome modification induced by hypoxia and lactate

The production of lactate under hypoxic conditions or by cancer cells was reported to promote the M2 polarization of tumor-associated macrophages. However, the exact effect of lactate on macrophages, particularly under hypoxic conditions, has remained largely elusive. In the present study, an in-depth bioinformatics analysis of previously published transcriptome data of macrophages was performed. A total of 6, 101 and 764 upregulated genes were identified in the lactate, hypoxia and hypoxia-lactate groups, respectively, whereas 4, 41 and 588 genes were downregulated in the same respective groups. Furthermore, differentially expressed genes (DEGs) of the hypoxia and hypoxia-lactate groups were significantly enriched in the hypoxia-inducible factor 1 (HIF-1) signaling pathway and the Hedgehog pathway. Upregulation of the mTOR and Hedgehog pathways in the hypoxia-lactate group was identified by gene set enrichment analysis. Furthermore, a set of HIF-1 pathway-associated genes was identified to be positively correlated with hypoxia using weighted gene co-expression network analysis. Lactate was indicated to inhibit the cell cycle in a hypoxia-independent manner. The DEGs of the hypoxia and hypoxia-lactate groups, including C-C motif chemokine receptor type 1 and 5, were enriched in the cytokine-cytokine receptor interaction pathway. In conclusion, under normoxic conditions, lactate exerted a weak effect on macrophages, while the combination of lactate and hypoxia markedly promoted the M2-polarization of macrophages via the HIF-1, Hedgehog and mTOR pathways. Lactate and hypoxia may also contribute to the formation of the spatial structure of tumor niches by inhibiting the proliferation of resident macrophages and by regulating the recruitment of peripheral macrophages.

Ultrastructure and function of the amoeboid microglial cells in the periventricular white matter in postnatal rat brain following a hypoxic exposure

The ameboid microglial cells (AMC), located in the periventricular white matter, were examined ultrastucturally in neonatal rats following a hypoxic exposure. For 10 min to 1 day, following the hypoxic exposure, a large number of glial cells with nuclear chromatin condensation, undergoing degeneration, were observed in the white matter. Such cells were often being phagocytosed by the AMC. At 3-7 days after the hypoxic exposure, the cytoplasm of many AMC contained a number of phagosomes whereas at 14-28 days a large amount of lipid accumulation was observed in them. AMC were labeled intensely with horseradish peroxidase (HRP) administered intraperitoneally following the hypoxic exposure. The phagocytosis of degenerating cells by the AMC and uptake of HRP by them indicates that these cells efficiently remove the degenerating cells/debris from the neonatal white matter following hypoxia in an attempt to protect it from any harmful substances that may be secreted by the degenerating cells or from serum derived substances that may enter the brain through blood circulation.