Role of prolyl hydroxylase domain proteins in bone metabolism

The effect of Hypoxia-Inducible Factor-1a stabilization on bone regeneration during distraction osteogenesis: A systematic review of animal studies

OBJECTIVE

This systematic review described Hypoxia-Inducible Factor-1a stabilization or upregulation approaches along with underlying signaling pathways and assessed bone regeneration, angiogenesis, and consolidation time during DO in animal models.

DESIGN

A comprehensive and systematic search of electronic databases including PubMed, Scopus, and ScienceDirect was performed till December 26, 2023. The search was limited to English articles, and no time restrictions were applied.

RESULTS

A total of 14 studies met the inclusion criteria and were included for final review. Four methods have been shown to activate the HIF pathway including genetic, pharmacological, mechanical, and cell preconditioning approaches. Deferoxamine (DFO) was administered as a pharmacological hypoxia-mimicking agent in many studies reporting acceptable outcomes on bone regeneration and acceleration of bone consolation. Applying mechanical loads at the optimal rate and amplitude serves as a minimally invasive approach with acceptable results. HIF-related signaling pathways increase osteogenesis and angiogenesis during DO, potentially through VHL/HIF-1a/VEGF, Wnt/β-catenin, and Mesenchymal-Epithelial transition (MET) signaling pathways.

CONCLUSION

Activation of HIF-related signaling pathways enhances and accelerates bone regeneration during the consolidation phase of distraction osteogenesis. The most feasible approach with the least side effects must be selected for further clinical studies.

HOTAIR Participation in Glycolysis and Glutaminolysis Through Lactate and Glutamate Production in Colorectal Cancer

Metabolic reprogramming plays a crucial role in cancer biology and the mechanisms underlying its regulation represent a promising study area. In this regard, the discovery of non-coding RNAs opened a new regulatory landscape, which is in the early stages of investigation. Using a differential expression model of HOTAIR, we evaluated the expression level of metabolic enzymes, as well as the metabolites produced by glycolysis and glutaminolysis. Our results demonstrated the regulatory effect of HOTAIR on the expression of glycolysis and glutaminolysis enzymes in colorectal cancer cells. Specifically, through the overexpression and inhibition of HOTAIR, we determined its influence on the expression of the enzymes PFKFB4, PGK1, LDHA, SLC1A5, GLUD1, and GOT1, which had a direct impact on lactate and glutamate production. These findings indicate that HOTAIR plays a significant role in producing "oncometabolites" essential to maintaining the bioenergetics and biomass necessary for tumor cell survival by regulating glycolysis and glutaminolysis.

Regulation of newly identified lysine lactylation in cancer

Metabolic reprogramming is a typical hallmark of cancer. Enhanced glycolysis in tumor cells leads to the accumulation of lactate, which is traditionally considered metabolic waste. With the development of high-resolution liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS), the lactate-derived, lysine lactylation(Kla), has been identified. Kla can alter the spatial configuration of chromatin and regulate the expression of corresponding genes. Metabolic reprogramming and epigenetic remodeling have been extensively linked. Accumulating studies have subsequently expanded the framework on the key roles of this protein translational modification (PTM) in tumors and have provided a new concept of cancer-specific regulation by Kla.

Role of prolyl hydroxylase/HIF-1 signaling in vascular calcification

Morbidity and mortality of chronic kidney disease (CKD) patients are largely associated with vascular calcification, an actively regulated process in which vascular smooth muscle cells (VSMCs) change into cells similar to osteocytes/chondrocytes, known as trans-differentiation. Cellular and systemic response to low oxygen (hypoxia) is regulated by the prolyl hydroxylase/hypoxia-inducible factor (HIF)-1 pathway. Recent studies highlighted that hypoxia-mediated activation of HIF-1 induces trans-differentiation of VSMCs into bone-forming type through an increase in osteo-/chondrogenic genes. Inhibition of the HIF-1 pathway abolished osteochondrogenic differentiation of VSMCs. Hypoxia strongly enhanced elevated phosphate-induced VSMC osteogenic trans-differentiation and calcification. HIF-1 was shown to be essential for phosphate enhanced VSMC calcification. O₂-dependent degradation HIF-1 is triggered by the prolyl hydroxylase domain proteins (PHD). Prolyl hydroxylase inhibitors, daprodustat and roxadustat, increase high phosphate-induced VC in VSMCs, stabilizing HIF-1α and activating the HIF-1 pathway in these cells. Whether the use of these PHD inhibitors to treat anemia in CKD patients will favor the development and progression of vascular calcification remains to be explored.

Contrasting effects of <i>Ksr2</i>, an obesity gene, on trabecular bone volume and bone marrow adiposity

Pathological obesity and its complications are associated with an increased propensity for bone fractures. Humans with certain genetic polymorphisms at the kinase suppressor of ras2 (KSR2) locus develop severe early-onset obesity and type 2 diabetes. Both conditions are phenocopied in mice with <i>Ksr2</i> deleted, but whether this affects bone health remains unknown. Here we studied the bones of global <i>Ksr2</i> null mice and found that <i>Ksr2</i> negatively regulates femoral, but not vertebral, bone mass in two genetic backgrounds, while the paralogous gene, <i>Ksr1</i>, was dispensable for bone homeostasis. Mechanistically, KSR2 regulates bone formation by influencing adipocyte differentiation at the expense of osteoblasts in the bone marrow. Compared with <i>Ksr2</i>'s known role as a regulator of feeding by its function in the hypothalamus, pair-feeding and osteoblast-specific conditional deletion of <i>Ksr2</i> reveals that <i>Ksr2</i> can regulate bone formation autonomously. Despite the gains in appendicular bone mass observed in the absence of <i>Ksr2</i>, bone strength, as well as fracture healing response, remains compromised in these mice. This study highlights the interrelationship between adiposity and bone health and provides mechanistic insights into how <i>Ksr2</i>, an adiposity and diabetic gene, regulates bone metabolism.