Oxygen sensing decoded: a Nobel concept in biology

Feedback loop between hypoxia and energy metabolic reprogramming aggravates the radioresistance of cancer cells

Radiotherapy is one of the mainstream approaches for cancer treatment, although the clinical outcomes are limited due to the radioresistance of tumor cells. Hypoxia and metabolic reprogramming are the hallmarks of tumor initiation and progression and are closely linked to radioresistance. Inside a tumor, the rate of angiogenesis lags behind cell proliferation, and the underdevelopment and abnormal functions of blood vessels in some loci result in oxygen deficiency in cancer cells, i.e., hypoxia. This prevents radiation from effectively eliminating the hypoxic cancer cells. Cancer cells switch to glycolysis as the main source of energy, a phenomenon known as the Warburg effect, to sustain their rapid proliferation rates. Therefore, pathways involved in metabolic reprogramming and hypoxia-induced radioresistance are promising intervention targets for cancer treatment. In this review, we discussed the mechanisms and pathways underlying radioresistance due to hypoxia and metabolic reprogramming in detail, including DNA repair, role of cancer stem cells, oxidative stress relief, autophagy regulation, angiogenesis and immune escape. In addition, we proposed the existence of a feedback loop between energy metabolic reprogramming and hypoxia, which is associated with the development and exacerbation of radioresistance in tumors. Simultaneous blockade of this feedback loop and other tumor-specific targets can be an effective approach to overcome radioresistance of cancer cells. This comprehensive overview provides new insights into the mechanisms underlying tumor radiosensitivity and progression.

CRISPR editing of anti-anemia drug target rescues independent preclinical models of retinitis pigmentosa

Retinitis pigmentosa (RP) is one of the most common forms of hereditary neurodegeneration. It is caused by one or more of at least 3,100 mutations in over 80 genes that are primarily expressed in rod photoreceptors. In RP, the primary rod-death phase is followed by cone death, regardless of the underlying gene mutation that drove the initial rod degeneration. Dampening the oxidation of glycolytic end products in rod mitochondria enhances cone survival in divergent etiological disease models independent of the underlying rod-specific gene mutations. Therapeutic editing of the prolyl hydroxylase domain-containing protein gene (PHD2, also known as Egln1) in rod photoreceptors led to the sustained survival of both diseased rods and cones in both preclinical autosomal-recessive and dominant RP models. Adeno-associated virus-mediated CRISPR-based therapeutic reprogramming of the aerobic glycolysis node may serve as a gene-agnostic treatment for patients with various forms of RP.

Pathological angiogenesis: mechanisms and therapeutic strategies

In multicellular organisms, angiogenesis, the formation of new blood vessels from pre-existing ones, is an essential process for growth and development. Different mechanisms such as vasculogenesis, sprouting, intussusceptive, and coalescent angiogenesis, as well as vessel co-option, vasculogenic mimicry and lymphangiogenesis, underlie the formation of new vasculature. In many pathological conditions, such as cancer, atherosclerosis, arthritis, psoriasis, endometriosis, obesity and SARS-CoV-2(COVID-19), developmental angiogenic processes are recapitulated, but are often done so without the normal feedback mechanisms that regulate the ordinary spatial and temporal patterns of blood vessel formation. Thus, pathological angiogenesis presents new challenges yet new opportunities for the design of vascular-directed therapies. Here, we provide an overview of recent insights into blood vessel development and highlight novel therapeutic strategies that promote or inhibit the process of angiogenesis to stabilize, reverse, or even halt disease progression. In our review, we will also explore several additional aspects (the angiogenic switch, hypoxia, angiocrine signals, endothelial plasticity, vessel normalization, and endothelial cell anergy) that operate in parallel to canonical angiogenesis mechanisms and speculate how these processes may also be targeted with anti-angiogenic or vascular-directed therapies.

Angiogenesis in abnormal uterine bleeding: a narrative review

BACKGROUND

Abnormal uterine bleeding (AUB) has a significant socioeconomic impact since it considerably impacts quality of life. Therapeutic options are frequently based on trial and error and do not target disease aetiology. Pathophysiological insight in this disease is required for the development of novel treatment options. If no underlying cause is found for the AUB (e.g. fibroids, adenomyosis, polyps), endometrial-AUB (AUB-E) is usually caused by a primary endometrium disorder. When AUB is induced by prescribed (exogenous) hormones, it is classified as iatrogenic-AUB (AUB-I). Considering vascular modulation and function, AUB-E and AUB-I both could potentially result from abnormal vascularization in the endometrium due to alterations in the process of angiogenesis and vascular maturation.

OBJECTIVE AND RATIONALE

We aim to investigate the fundamental role of angiogenesis and vascular maturation in patients with AUB and hypothesize that aberrant endometrial angiogenesis has an important role in the aetiology of both AUB-E and AUB-I, possibly through different mechanisms.

SEARCH METHODS

A systematic literature search was performed until September 2021 in the Cochrane Library Databases, Embase, PubMed, and Web of Science, with search terms such as angiogenesis and abnormal uterine bleeding. Included studies reported on angiogenesis in the endometrium of premenopausal women with AUB-E or AUB-I. Case reports, letters, reviews, editorial articles, and studies on AUB with causes classified by the International Federation of Gynecology and Obstetrics as myometrial, oncological, or infectious, were excluded. Study quality was assessed by risk of bias, using the Cochrane tool and the Newcastle-Ottawa Scale.

OUTCOMES

Thirty-five out of 2158 articles were included. In patients with AUB-E, vascular endothelial growth factor A and its receptors (1 and 2), as well as the angiopoietin-1:angiopoietin-2 ratio and Tie-1, were significantly increased. Several studies reported on the differential expression of other pro- and antiangiogenic factors in patients with AUB-E, suggesting aberrant vascular maturation and impaired vessel integrity. Overall, endometrial microvessel density (MVD) was comparable in patients with AUB-E and controls. Interestingly, patients with AUB-I showed a higher MVD and higher expression of proangiogenic factors when compared to controls, in particular after short-term hormone exposure. This effect was gradually lost after longer-term exposure, while alterations in vessel maturation were observed after both short- and long-term exposures.

WIDER IMPLICATIONS

AUB-E and AUB-I are most likely associated with aberrant endometrial angiogenesis and impaired vessel maturation. This review supports existing evidence that increased proangiogenic and decreased antiangiogenic factors cause impaired vessel maturation, resulting in more fragile and permeable vessels. This matches our hypothesis and these mechanisms appear to play an important role in the pathophysiology of AUB-E and AUB-I. Exploring the alterations in angiogenesis in these patients could provide treatment targets for AUB.

Hypoxia as a Driving Force of Pluripotent Stem Cell Reprogramming and Differentiation to Endothelial Cells

Inadequate supply of oxygen (O₂) is a hallmark of many diseases, in particular those related to the cardiovascular system. On the other hand, tissue hypoxia is an important factor regulating (normal) embryogenesis and differentiation of stem cells at the early stages of embryonic development. In culture, hypoxic conditions may facilitate the derivation of embryonic stem cells (ESCs) and the generation of induced pluripotent stem cells (iPSCs), which may serve as a valuable tool for disease modeling. Endothelial cells (ECs), multifunctional components of vascular structures, may be obtained from iPSCs and subsequently used in various (hypoxia-related) disease models to investigate vascular dysfunctions. Although iPSC-ECs demonstrated functionality in vitro and in vivo, ongoing studies are conducted to increase the efficiency of differentiation and to establish the most productive protocols for the application of patient-derived cells in clinics. In this review, we highlight recent discoveries on the role of hypoxia in the derivation of ESCs and the generation of iPSCs. We also summarize the existing protocols of hypoxia-driven differentiation of iPSCs toward ECs and discuss their possible applications in disease modeling and treatment of hypoxia-related disorders.

Oncometabolites lactate and succinate drive pro-angiogenic macrophage response in tumors

Macrophages are innate phagocytic leukocytes that are highly present in solid tumors, where they are referred to as tumor-associated macrophages (TAMs). In solid tumors, the microenvironment is often immunosuppressive and hypoxic regions are prevalent. These hypoxic conditions impose tumor cells to reprogram their metabolism, shifting from oxidative phosphorylation to anaerobic glycolysis. This so-called glycolytic switch enables hypoxic tumor cells to survive, proliferate, and eventually to outcompete untransformed cells. The hypoxia-induced change in tumor cell metabolism leads to the production of oncometabolites, among which are the glycolytic end-metabolite lactate and the tricarboxylic acid cycle intermediate succinate. TAMs can react to these oncometabolites, resulting in an altered maturation and the adoption of pro-angiogenic features. These angiogenesis-promoting TAMs have been reported to cooperate with tumor cells in the formation of new vessels, and even have been considered an important cause of resistance against anti-angiogenic therapies. For a long time, the mechanisms by which lactate and succinate activated pro-angiogenic TAMs were not understood. Researchers now start to unravel and understand some of the underlying mechanisms. Here, the importance of microenvironmental cues in inducing different macrophage activation states is discussed, as well as the role of hypoxia in the recruitment and activation of pro-angiogenic macrophages. In addition, the latest findings on the oncometabolites lactate and succinate in the activation of angiogenesis supporting macrophages are reviewed. Finally, various oncometabolite-targeting therapeutic strategies are proposed that could improve the response to anti-angiogenic therapies. SIGNIFICANCE STATEMENT: Tumor-associated macrophages (TAMs) are known promotors of tumor neovascularization, and significantly contribute to the emergence of resistance to anti-angiogenic therapies. Recent evidence suggests that the angiogenesis promoting phenotype of TAMs can be activated by hypoxic tumor cell-derived oncometabolites, including lactate and succinate. Here, the latest findings into the lactate- and succinate-mediated mechanistic activation of pro-angiogenic TAMs are reviewed, and therapeutic strategies that interfere with this mechanism and may delay or even prevent acquired resistance to anti-angiogenic agents are discussed.

Presidential Address Kidney Week 2019: Winning the War on Kidney Diseases: The Time Is Now

The American Society of Nephrology Presidential Address was delivered by Mark Rosenberg at Kidney Week 2019 on November 7, 2019 in Washington, DC. The Address describes a remarkable alignment-a syzygy of policy, science, innovation accelerators, clinical trials, clinical care delivery, and activated patients-that exists today in the kidney space. As a community, we must ensure that the strategies developed to take advantage of this alignment, such as Advancing American Kidney Health, succeed. We must overcome our current challenges to thrive as a meaningful specialty. We have an incredible opportunity to come together as a kidney community to ensure success that realigns the priorities and incentives in kidney medicine to better achieve kidney health for all people throughout the world. The time is now to act.

Adenylosuccinate lyase hydroxylation contributes to triple negative breast cancer via the activation of cMYC

Hydroxylation is a post-translational modification affecting protein stability, activity or interactome. We identified adenylosuccinate lyase (ADSL) as a novel hydroxylation substrate in triple negative breast cancer. Hydroxylation affects ADSL enzymatic activity and, therefore, adenosine levels. Adenosine, in turn, favors the translation of cMYC, triggering its oncogenic downstream cascade.