Dual role of MUC1 mucin in kidney ischemia-reperfusion injury: Nephroprotector in early phase, but pro-fibrotic in late phase.

Acute kidney injury (AKI) is characterized by acute tubular necrosis (ATN) which involves mainly proximal tubules. Past AKI is associated with higher risk of chronic kidney disease (CKD). The MUC1 mucin is a large glycoprotein responsible for epithelial protection and locates to convoluted distal tubules and collecting ducts. Since MUC1 activates the epithelial-mesenchymal transition (EMT) in carcinoma cells, we hypothesized that MUC1 could be involved in epithelial tubular cell plasticity, a process that not only accompanies epithelial repair, but also participates into kidney fibrosis, histological substratum of CKD. In cultured human proximal cells and in human kidney allograft biopsies, we observed MUC1 induction in proximal tubules displaying ATN. Transient MUC1 induction localized with mesenchymal and stem-cell markers and was associated in vitro with reduced anoikis. In a mouse ischemia-reperfusion (IR) model, Muc1 expression mitigates severe tubular injury, as WT displayed less ATN than Muc1 KO mice. But, WT mice displayed more severe kidney fibrosis than Muc1 KO 28days after ischemia. Besides, sustained Muc1 expression in WT was associated with less kidney M2 macrophages. Human kidney biopsies performed within the first week (W1) of transplantation in the context of IR showed MUC1 W1 induction associated with EMT markers. Protocol biopsies performed 3months after demonstrated sustained abnormal MUC1 induction in atrophic tubules within kidney fibrosis. Altogether these data showed that sustained abnormal MUC1 induction accompanies failing epithelial repair, chronic inflammation and kidney fibrosis. In conclusion, MUC1 exerts opposite effects during kidney response to IR: first protective and then harmful.

Human Alternative Macrophages Populate Calcified Areas of Atherosclerotic Lesions and Display Impaired RANKL-Induced Osteoclastic Bone Resorption Activity.

RATIONALE: Vascular calcification is a process similar to bone formation leading to an inappropriate deposition of calcium phosphate minerals in advanced atherosclerotic plaques. Monocyte-derived macrophages, located in atherosclerotic lesions and presenting heterogeneous phenotypes, from classical proinflammatory M1 to alternative anti-inflammatory M2 macrophages, could potentially display osteoclast-like functions. OBJECTIVE: To characterize the phenotype of macrophages located in areas surrounding the calcium deposits in human atherosclerotic plaques. METHODS AND RESULTS: Macrophages near calcium deposits display an alternative phenotype being both CD68 and mannose receptor-positive, expressing carbonic anhydrase type II, but relatively low levels of cathepsin K. In vitro interleukin-4-polarization of human primary monocytes into macrophages results in lower expression and activity of cathepsin K compared with resting unpolarized macrophages. Moreover, interleukin-4 polarization lowers expression levels of the osteoclast transcriptional activator nuclear factor of activated T cells type c-1, associated with increased gene promoter levels of the transcriptional repression mark H3K27me3 (histone 3 lysine 27 trimethylation). Despite higher expression of the receptor activator of nuclear factor κB receptor, receptor activator of nuclear factor κB ligand/macrophage colony-stimulating factor induction of nuclear factor of activated T cells type c-1 and cathepsin K expression is defective in these macrophages because of reduced Erk/c-fos-mediated downstream signaling resulting in impaired bone resorption capacity. CONCLUSIONS: These results indicate that macrophages surrounding calcium deposits in human atherosclerotic plaques are phenotypically defective being unable to resorb calcification.

HDL does not influence the polarization of human monocytes toward an alternative phenotype.

BACKGROUND: Macrophages are crucial cells in the pathogenesis of atherosclerosis. Macrophages are plastic cells which can switch from a classical pro-inflammatory M1 to an alternative anti-inflammatory M2 macrophage phenotype, depending on the environmental stimuli. Because high-density lipoprotein (HDL) cholesterol levels are inversely correlated to cardiovascular disease and since HDL displays anti-inflammatory properties, we investigated whether HDL can affect alternative macrophage differentiation of primary human monocytes in the presence of interleukin (IL)-4, a M2 macrophage polarization driver, in vitro and ex vivo. METHODS AND RESULTS: M2 macrophages are highly responsive to HDL stimulation, since the expression of pentraxin 3 (PTX3), a well known HDL target gene, is induced by HDL more strongly in M2 macrophages than in control unpolarized resting macrophages (RM). As expected, the expression of M2 markers, such as Mannose Receptor (MR), CD200 Receptor (CD200R), Coagulation factor XIII A1 (F13A1), IL-1 receptor antagonist (IL-1RA) and IL10, was induced in IL-4 polarized M2 macrophages compared to RM. However, incubation with HDL added in vitro did not modulate the gene expression of M2 macrophage polarization markers. Moreover, monocytes isolated from subjects with genetically low HDL levels, carrying ABCA1 or LCAT mutations, differentiated ex vivo into M2 macrophages without any difference in the alternative macrophage marker expression profile. CONCLUSIONS: These in vitro and ex vivo results indicate that, contrary to mouse macrophages, HDL does not influence macrophage M2 polarization of human monocyte-derived macrophages. Thus, the anti-inflammatory properties of HDL in humans are probably not related to the enhancement of the M2 macrophage phenotype.

Liver X receptor activation stimulates iron export in human alternative macrophages.

RATIONALE: In atherosclerotic plaques, iron preferentially accumulates in macrophages where it can exert pro-oxidant activities. OBJECTIVE: The objective of this study was, first, to better characterize the iron distribution and metabolism in macrophage subpopulations in human atherosclerotic plaques and, second, to determine whether iron homeostasis is under the control of nuclear receptors, such as the liver X receptors (LXRs). METHODS AND RESULTS: Here we report that iron depots accumulate in human atherosclerotic plaque areas enriched in CD68 and mannose receptor (MR)-positive (CD68(+)MR(+)) alternative M2 macrophages. In vitro IL-4 polarization of human monocytes into M2 macrophages also resulted in a gene expression profile and phenotype favoring iron accumulation. However, M2 macrophages on iron exposure acquire a phenotype favoring iron release, through a strong increase in ferroportin expression, illustrated by a more avid oxidation of extracellular low-density lipoprotein by iron-loaded M2 macrophages. In line, in human atherosclerotic plaques, CD68(+)MR(+) macrophages accumulate oxidized lipids, which activate LXRα and LXRß, resulting in the induction of ABCA1, ABCG1, and apolipoprotein E expression. Moreover, in iron-loaded M2 macrophages, LXR activation induces nuclear factor erythroid 2-like 2 expression, thereby increasing ferroportin expression, which, together with a decrease of hepcidin mRNA levels, promotes iron export. CONCLUSIONS: These data identify a role for M2 macrophages in iron handling, a process regulated by LXR activation.