Human prolyl‐hydroxylases (PHDs) are hypoxia‐sensing 2‐oxoglutarate (2OG) oxygenases, catalysis by which suppresses the transcription of hypoxia‐inducible factor target genes. PHD inhibition enables ...the treatment of anaemia/ischaemia‐related disease. The PHD inhibitor Molidustat is approved for the treatment of renal anaemia; it differs from other approved/late‐stage PHD inhibitors in lacking a glycinamide side chain. The first reported crystal structures of Molidustat and IOX4 (a brain‐penetrating derivative) complexed with PHD2 reveal how their contiguous triazole, pyrazolone and pyrimidine/pyridine rings bind at the active site. The inhibitors bind to the active‐site metal in a bidentate manner through their pyrazolone and pyrimidine nitrogens, with the triazole π‐π‐stacking with Tyr303 in the 2OG binding pocket. Comparison of the new structures with other PHD inhibitor complexes reveals differences in the conformations of Tyr303, Tyr310, and a mobile loop linking β2–β3, which are involved in dynamic substrate binding/product release.
Ring binder: Co‐crystal structures of human PHD2 with Molidustat and a related inhibitor provide insight into their mode of inhibition. The pyrazolone‐pyrimidine rings of Molidustat chelate the active‐site metal ion, and its triazole ring makes a π‐π‐stacking interaction with Tyr303. The results reveal altered conformations of PHD2 residues, including Tyr303 and Tyr310 on binding of Fe‐chelating PHD inhibitors.
Objectives
Necrotizing sialometaplasia (NS) is an uncommon reactive lesion involving the minor salivary glands. This study aimed to investigate the expression of hypoxia‐inducible factor alpha ...(HIF‐1α), vascular endothelial growth factor (VEGF), and epithelial growth factor receptor (EGFR) in the pathogenesis of NS.
Methods
Paraffin‐embedded tissue sections from 10 cases of NS were immunohistochemically stained for HIF‐1α, VEGF, and EGFR. A semiquantitative morphometric analysis was performed and compared with normal palatal salivary glands and traumatic ulcerations.
Results
Hypoxia‐inducible factor alpha staining was observed in most elements of the affected area, the acini and ducts of the involved salivary glands as well as in the inflammatory infiltrate, the endothelial cells, and stromal cells. HIF‐1α was almost absent in the control glands (P < 0.0001). VEGF staining was positive in the stromal capillaries and in the inflammatory infiltrate. The expression was higher in cases of NS compared with the normal salivary glands (P < 0.001). EGFR was expressed in the surface epithelium, the pseudo‐epitheliomatous hyperplasia, and the islands of squamous metaplasia. VEGF expression in traumatic ulcerations was lower than that in cases of NS.
Conclusion
This study provides molecular evidence to the role of hypoxia in NS; HIF‐1α, the main regulator of hypoxia, was expressed in the infarcted salivary glands, EGFR in the metaplastic epithelium and VEGF in the stromal capillaries, all three components are the key factors induced by hypoxia.
: Articular cartilage is an avascular tissue with significantly reduced levels of oxygen and nutrients compared to plasma and synovial fluid. Therefore, chondrocyte survival and cartilage ...homeostasis require effective mechanisms for oxygen and nutrient signaling. To gain a better understanding of the mechanisms responsible for oxygen and nutrient sensing in chondrocytes, we investigated the effects of hypoxic stimulation induced by cobalt chloride treatment (a hypoxia‐mimetic) on glucose uptake and lactate production in chondrocytes. We also studied the effects of cobalt chloride and glucose deprivation on the expression and secretion of active MMP‐2. Primary cultures of articular chondrocytes were either maintained in 20% O2 (normoxia) or exposed to the hypoxia‐mimetic cobalt chloride for up to 24 h at the following concentrations: 15 μM, 37.5 μM, and 75 μM. Glucose transport was determined by measuring the net uptake of nonmetabolizable 2‐deoxy‐d‐2, 6‐3H glucose into chondrocytes. Active MMP‐2 secretion was assayed by gelatin zymography. Lactic acid production was assayed using a lactate kit. Exposure to cobalt chloride significantly increased the uptake of 2‐deoxy‐d‐2, 6‐3H glucose and the production of lactate. Glucose deprivation and cobalt chloride treatment increased levels of active MMP‐2 in the culture medium. Our results suggest that these metabolic alterations are important events during adaptation to hypoxia. Upregulation of MMP‐2 and the build‐up of lactic acid will have detrimental effects on the extracellular matrix and may contribute to the pathogenesis and progression of osteoarthritis (OA).
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