High phosphate and calcium induce osteoblastic phenotype switching and calcification of corneal epithelial cells in a Runx2-dependent and synergistic manner; a possible mechanism of chronic kidney disease-associated corneal calcification.

Patients with advanced chronic kidney disease (CKD) have elevated circulating calcium × phosphate product levels and exhibit soft tissue calcification. Besides the cardiovascular system, calcification is commonly observed in the cornea in CKD patients on hemodialysis. Cardiovascular calcification is a cell-mediated, highly regulated process, and we hypothesized that a similar regulatory mechanism is implicated in corneal calcification with the involvement of corneal epithelial cells (CECs). We established a mouse model of CKD-associated corneal calcification by inducing CKD in DBA/2J mice with an adenine and high phosphate diet. CKD was associated with aorta and corneal calcification as detected by OsteoSense staining and corneal Ca measurement (1.67-fold elevation, p < 0.001). In vitro, excess phosphate and Ca induced human CEC calcification in a dose-dependent and synergistic manner, without any influence on cell viability. High phosphate and Ca-containing osteogenic medium (OM; 2.5 mmol/L excess phosphate and 0.6 mmol/L excess Ca over control) increased the protein expression of Runx2 and induced its nuclear translocation. OM increased the expression of the bone-specific Ca-binding protein osteocalcin (130-fold increase, p < 0.001). Silencing of Runx2 attenuated OM-induced CEC calcification. Immunohistology revealed upregulation of Runx2 and overlapping between the Runx2 and the Alizarin red positive areas of calcification in the cornea of CKD mice. This work sheds light on the mechanism of CKD-induced corneal calcification and provides tools to test calcification inhibitors for the prevention of this detrimental process.

High glucose promotes osteogenic differentiation of human lens epithelial cells through hypoxia-inducible factor (HIF) activation.

Cataract, a leading cause of blindness, is characterised by lens opacification. Type 2 diabetes is associated with a two- to fivefold higher prevalence of cataracts. The risk of cataract formation increases with the duration of diabetes and the severity of hyperglycaemia. Hydroxyapatite deposition is present in cataractous lenses that could be the consequence of osteogenic differentiation and calcification of lens epithelial cells (LECs). We hypothesised that hyperglycaemia might promote the osteogenic differentiation of human LECs (HuLECs). Osteogenic medium (OM) containing excess phosphate and calcium with normal (1 g/L) or high (4.5 g/L) glucose was used to induce HuLEC calcification. High glucose accelerated and intensified OM-induced calcification of HuLECs, which was accompanied by hyperglycaemia-induced upregulation of the osteogenic markers Runx2, Sox9, alkaline phosphatase and osteocalcin, as well as nuclear translocation of Runx2. High glucose-induced calcification was abolished in Runx2-deficient HuLECs. Additionally, high glucose stabilised the regulatory alpha subunits of hypoxia-inducible factor 1 (HIF-1), triggered nuclear translocation of HIF-1α and increased the expression of HIF-1 target genes. Gene silencing of HIF-1α or HIF-2α attenuated hyperglycaemia-induced calcification of HuLECs, while hypoxia mimetics (desferrioxamine, CoCl2) enhanced calcification of HuLECs under normal glucose conditions. Overall, this study suggests that high glucose promotes HuLEC calcification via Runx2 and the activation of the HIF-1 signalling pathway. These findings may provide new insights into the pathogenesis of diabetic cataracts, shedding light on potential factors for intervention to treat this sight-threatening condition.

Hypoxia-inducible factor activation promotes osteogenic transition of valve interstitial cells and accelerates aortic valve calcification in a mice model of chronic kidney disease.

Introduction: Valve calcification (VC) is a widespread complication in chronic kidney disease (CKD) patients. VC is an active process with the involvement of in situ osteogenic transition of valve interstitial cells (VICs). VC is accompanied by the activation of hypoxia inducible factor (HIF) pathway, but the role of HIF activation in the calcification process remains undiscovered. Methods and result: Using in vitro and in vivo approaches we addressed the role of HIF activation in osteogenic transition of VICs and CKD-associated VC. Elevation of osteogenic (Runx2, Sox9) and HIF activation markers (HIF-1α and HIF-2α) and VC occurred in adenine-induced CKD mice. High phosphate (Pi) induced upregulation of osteogenic (Runx2, alkaline-phosphatase, Sox9, osteocalcin) and hypoxia markers (HIF-1α, HIF-2α, Glut-1), and calcification in VICs. Down-regulation of HIF-1α and HIF-2α inhibited, whereas further activation of HIF pathway by hypoxic exposure (1% O2) or hypoxia mimetics [desferrioxamine, CoCl2, Daprodustat (DPD)] promoted Pi-induced calcification of VICs. Pi augmented the formation of reactive oxygen species (ROS) and decreased viability of VICs, whose effects were further exacerbated by hypoxia. N-acetyl cysteine inhibited Pi-induced ROS production, cell death and calcification under both normoxic and hypoxic conditions. DPD treatment corrected anemia but promoted aortic VC in the CKD mice model. Discussion: HIF activation plays a fundamental role in Pi-induced osteogenic transition of VICs and CKD-induced VC. The cellular mechanism involves stabilization of HIF-1α and HIF-2α, increased ROS production and cell death. Targeting the HIF pathways may thus be investigated as a therapeutic approach to attenuate aortic VC.

Indolepropionic Acid, a Metabolite of the Microbiome, Has Cytostatic Properties in Breast Cancer by Activating AHR and PXR Receptors and Inducing Oxidative Stress.

Oncobiotic transformation of the gut microbiome may contribute to the risk of breast cancer. Recent studies have provided evidence that the microbiome secretes cytostatic metabolites that inhibit the proliferation, movement, and metastasis formation of cancer cells. In this study, we show that indolepropionic acid (IPA), a bacterial tryptophan metabolite, has cytostatic properties. IPA selectively targeted breast cancer cells, but it had no effects on non-transformed, primary fibroblasts. In cell-based and animal experiments, we showed that IPA supplementation reduced the proportions of cancer stem cells and the proliferation, movement, and metastasis formation of cancer cells. These were achieved through inhibiting epithelial-to-mesenchymal transition, inducing oxidative and nitrosative stress, and boosting antitumor immune response. Increased oxidative/nitrosative stress was due to the IPA-mediated downregulation of nuclear factor erythroid 2-related factor 2 (NRF2), upregulation of inducible nitric oxide synthase (iNOS), and enhanced mitochondrial reactive species production. Increased oxidative/nitrosative stress led to cytostasis and reductions in cancer cell stem-ness. IPA exerted its effects through aryl hydrocarbon receptor (AHR) and pregnane X receptor (PXR) receptors. A higher expression of PXR and AHR supported better survival in human breast cancer patients, highlighting the importance of IPA-elicited pathways in cytostasis in breast cancer. Furthermore, AHR activation and PXR expression related inversely to cancer cell proliferation level and to the stage and grade of the tumor. The fecal microbiome's capacity for IPA biosynthesis was suppressed in women newly diagnosed with breast cancer, especially with stage 0. Bacterial indole biosynthesis showed correlation with lymphocyte infiltration to tumors in humans. Taken together, we found that IPA is a cytostatic bacterial metabolite, the production of which is suppressed in human breast cancer. Bacterial metabolites, among them, IPA, have a pivotal role in regulating the progression but not the initiation of the disease.

Cadaverine, a metabolite of the microbiome, reduces breast cancer aggressiveness through trace amino acid receptors.

Recent studies showed that changes to the gut microbiome alters the microbiome-derived metabolome, potentially promoting carcinogenesis in organs that are distal to the gut. In this study, we assessed the relationship between breast cancer and cadaverine biosynthesis. Cadaverine treatment of Balb/c female mice (500 nmol/kg p.o. q.d.) grafted with 4T1 breast cancer cells ameliorated the disease (lower mass and infiltration of the primary tumor, fewer metastases, and lower grade tumors). Cadaverine treatment of breast cancer cell lines corresponding to its serum reference range (100-800 nM) reverted endothelial-to-mesenchymal transition, inhibited cellular movement and invasion, moreover, rendered cells less stem cell-like through reducing mitochondrial oxidation. Trace amino acid receptors (TAARs), namely, TAAR1, TAAR8 and TAAR9 were instrumental in provoking the cadaverine-evoked effects. Early stage breast cancer patients, versus control women, had reduced abundance of the CadA and LdcC genes in fecal DNA, both responsible for bacterial cadaverine production. Moreover, we found low protein expression of E. coli LdcC in the feces of stage 1 breast cancer patients. In addition, higher expression of lysine decarboxylase resulted in a prolonged survival among early-stage breast cancer patients. Taken together, cadaverine production seems to be a regulator of early breast cancer.