Breakthrough Science: Hypoxia-Inducible Factors, Oxygen Sensing, and Disorders of Hematopoiesis

Hypoxia-associated autophagy flux dysregulation in human cancers

A general feature of cancer is hypoxia, determined as low oxygen levels. Low oxygen levels may cause cells to alter in ways that contribute to tumor growth and resistance to treatment. Hypoxia leads to variations in cancer cell metabolism, angiogenesis and metastasis. Furthermore, a hypoxic tumor microenvironment might induce immunosuppression. Moreover, hypoxia has the potential to impact cellular processes, such as autophagy. Autophagy refers to the catabolic process by which damaged organelles and toxic macromolecules are broken down. The abnormal activation of autophagy has been extensively recorded in human tumors and it serves as a regulator of cell growth, spread to other parts of the body, and resistance to treatment. There is a correlation between hypoxia and autophagy in human malignancies. Hypoxia can regulate the activity of AMPK, mTOR, Beclin-1, and ATGs to govern autophagy in human malignancies. Furthermore, HIF-1α, serving as an indicator of low oxygen levels, controls the process of autophagy. Hypoxia-induced autophagy has a crucial role in regulating the growth, spread, and resistance to treatment in human malignancies. Hypoxia-induced regulation of autophagy can impact other mechanisms of cell death, such as apoptosis. Chemoresistance and radioresistance have become significant challenges in recent years. Hypoxia-mediated autophagy plays a crucial role in determining the response to these therapeutic treatments.

Deletion of prolyl hydroxylase domain-containing enzyme 3 (phd3) in zebrafish facilitates hypoxia tolerance

Prolyl hydroxylase domain (PHD)-containing enzyme 3 (PHD3) belongs to the Caenorhabditis elegans gene egl-9 family of prolyl hydroxylases. PHD3 catalyzes proline hydroxylation of hypoxia-inducible factor α (HIF-α) and promotes HIF-α proteasomal degradation through coordination with the pVHL complex under normoxic conditions. However, the relationship between PHD3 and the hypoxic response is not well understood. In this study, we used quantitative real-time PCR assay and O-dianisidine staining to characterize the hypoxic response in zebrafish deficient in phd3. We found that the hypoxia-responsive genes are upregulated and the number of erythrocytes was increased in phd3-null zebrafish compared with their wild-type siblings. On the other hand, we show overexpression of phd3 suppresses HIF-transcriptional activation. In addition, we demonstrate phd3 promotes polyubiquitination of zebrafish hif-1/2α proteins, leading to their proteasomal degradation. Finally, we found that compared with wild-type zebrafish, phd3-null zebrafish are more resistant to hypoxia treatment. Therefore, we conclude phd3 has a role in hypoxia tolerance. These results highlight the importance of modulation of the hypoxia signaling pathway by phd3 in hypoxia adaptation.

Tumor microenvironment diversity and plasticity in cancer multidrug resistance

Multidrug resistance (MDR) poses a significant obstacle to effective cancer treatment, and the tumor microenvironment (TME) is crucial for MDR development and reversal. The TME plays an active role in promoting MDR through several pathways. However, a promising therapeutic approach for battling MDR involves targeting specific elements within the TME. Therefore, this comprehensive review elaborates on the research developments regarding the dual role of the TME in promoting and reversing MDR in cancer. Understanding the complex role of the TME in promoting and reversing MDR is essential to developing effective cancer therapies. Utilizing the adaptability of the TME by targeting novel TME-specific factors, utilizing combination therapies, and employing innovative treatment strategies can potentially combat MDR and achieve personalized treatment outcomes for patients with cancer.

Engineered hematopoietic and immune cells derived from human pluripotent stem cells

For the past decade, significant advances have been achieved in human hematopoietic stem cell (HSC) transplantation for treating various blood diseases and cancers. However, challenges remain with the quality control, amount, and cost of HSCs and HSC-derived immune cells. The advent of human pluripotent stem cells (hPSCs) may transform HSC transplantation and cancer immunotherapy by providing a cost-effective and scalable cell source for fundamental studies and translational applications. In this review, we discuss the current developments in the field of stem cell engineering for hematopoietic stem and progenitor cell (HSPC) differentiation and further differentiation of HSPCs into functional immune cells. The key advances in stem cell engineering include the generation of HSPCs from hPSCs, genetic modification of hPSCs, and hPSC-derived HSPCs for improved function, further differentiation of HPSCs into functional immune cells, and applications of cell culture platforms for hematopoietic cell manufacturing. Current challenges impeding the translation of hPSC-HSPCs and immune cells as well as further directions to address these challenges are also discussed.

The association of hypoxia-inducible factor-1α and hypoxia-inducible factor-2α protein expression with clinicopathological characteristics in papillary thyroid carcinoma: A meta-analysis

OBJECTIVE

To investigate the correlation of hypoxia-inducible factor-1α (HIF-1α) and hypoxia-inducible factor-2α (HIF-2α) protein expression with clinicopathologic characteristics in patients with papillary thyroid carcinoma (PTC) through a meta-analysis.

METHODS

PubMed, Embase, Web of Science, Cochrane, CNKI, Wanfang, and VIP databases were searched from the establishment of the database to February 2023. The New castle-Ottawa Scale was used to evaluate the quality of the literature. Rev Man 5.3 and Stata14.0 were used to conduct a meta-analysis of the included studies.

RESULTS

Twenty-eight articles with 2346 samples were included in the Meta-analysis. Compared with normal thyroid tissues, HIF-1α and HIF-2α proteins were highly expressed in PTC tumor tissues. High expression of HIF-1α protein was associated with tumor size (odds ratio [OR] = 4.50, 95% confidence interval [CI]: 2.88-7.04, P < .00001), lymph node metastasis (OR = 4.76, 95% CI: 3.78-5.99, P < .00001), TNM stage (OR = 3.67, 95% CI: 2.68-5.03, P < .00001), capsular invasion (OR = 2.30, 95% CI: 1.43-3.71, P = .0006 < .05), and extrathyroidal extension (OR = 10.96, 95% CI: 4.80-25.02, P < .00001). High expression of HIF-2α protein was associated with lymph node metastasis (OR = 4.18, 95% CI: 2.63-6.65, P < .00001), TNM stage (OR = 2.56, 95% CI: 1.36-4.82, P = .004 < .05), and capsular invasion (OR = 3.84, 95% CI: 1.66-8.88, P = .002 < .05). In addition, we concluded for the first time that there was a statistically significant difference in the expression of HIF-1α and HIF-2α in PTC patients (OR = 2.36, 95% CI: 1.26-4.42, P = .007 < .05).

CONCLUSIONS

The high expression of HIF-1α and HIF-2α proteins is closely related to some clinicopathological parameters of PTC, and can provide potential biological indicators for the diagnosis and prognosis of PTC.

Therapeutics of managing reduced red cell mass associated with chronic kidney disease - Is there a case for earlier intervention?

Reduced red cell mass is a poor prognostic indicator in chronic kidney disease (CKD) patients. Whilst overt anaemia impacts on the quality of life of patients with CKD, lowered red cell mass may also compromise oxygen delivery to proximal tubular cells and contribute to progressive kidney injury. Epidemiological data from cats with CKD support this hypothesis although controlled interventional studies involving drugs that raise red cell mass in trials designed to test this hypothesis are lacking in both human and veterinary medicine. Recombinant analogues of erythropoietin (EPO) are currently standard of care for human CKD patients where low red cell mass impacts on their quality of life. Resistance to EPO is encountered in 20% to 40% of patients treated, probably due to functional iron deficiency, reflecting the difficulties of managing iron deficiency associated with the chronic inflammation of CKD. Similar issues are likely faced in managing anaemia in feline CKD although published data on the use of human EPO analogues are limited as such treatment in cats risks antibody formation resulting in red cell aplasia and transfusion dependency and so is reserved for late stage cases only. This article reviews the recent alternative therapeutic approach to increase red cell mass using HIF-prolyl hydroxylase inhibitors and explains their mode of action and theoretical advantages over EPO analogues in the context of iron metabolism. The results of human clinical trials and the potential benefit of adopting this approach in feline CKD patients are discussed.

Hypoxia-inducible factors: cancer progression and clinical translation

Hypoxia-inducible factors (HIFs) are master regulators of oxygen homeostasis that match O2 supply and demand for each of the 50 trillion cells in the adult human body. Cancer cells co-opt this homeostatic system to drive cancer progression. HIFs activate the transcription of thousands of genes that mediate angiogenesis, cancer stem cell specification, cell motility, epithelial-mesenchymal transition, extracellular matrix remodeling, glucose and lipid metabolism, immune evasion, invasion, and metastasis. In this Review, the mechanisms and consequences of HIF activation in cancer cells are presented. The current status and future prospects of small-molecule HIF inhibitors for use as cancer therapeutics are discussed.