Vascular stiffening in aging females with a hypertension-induced HIF2A gain-of-function mutation

Pulmonary arterial hypertension (PAH) is more prevalent in females than males; the causes of this sex difference have not been adequately explored. Gain-of-function (GOF) mutations in hypoxia-inducible factor 2α (HIF2A) lead to PAH and thrombotic consequences in patients and mice. Additionally, multiple emerging studies suggest that elevated systemic arterial stiffening (SAS) occurs in PAH; this could have critical prognostic value. Here, we utilized a HIF2A GOF mouse model to determine how SAS can be used as a prognosticator in sex-divergent PAH. We analyzed survival, vascular mechanics, and vascular phenotypes in young adult (8-16 weeks) and middle age (9-12 months) Hif2a GOF mice. We find that Hif2a heterozygous (HT) female mice, but not Hif2a HT male mice, exhibit poor survival, SAS upon aging, and decreased ability to withstand repeated physiological strain. Hif2a HT female mice also display thickening of the adventitial intima and increased collagen I and collagen III in all layers of the thoracic aorta. Our findings demonstrate differing PAH progression in female and male Hif2a GOF mice. Specifically, alterations in extracellular matrix (ECM) content led to vascular stiffening in aged females, resulting in poor survival. Moreover, we show that SAS emerges early in mice with PAH by coupling studies of vascular mechanics and analyzing vascular structure and composition. Importantly, we present a model for assessing sex differences in hereditary PAH progression and sex-specific prognosis, proposing that aortic stiffening can be used to prognosticate future poor outcomes in PAH.

Erythroid mitochondrial retention triggers myeloid-dependent type I interferon in human SLE

Emerging evidence supports that mitochondrial dysfunction contributes to systemic lupus erythematosus (SLE) pathogenesis. Here we show that programmed mitochondrial removal, a hallmark of mammalian erythropoiesis, is defective in SLE. Specifically, we demonstrate that during human erythroid cell maturation, a hypoxia-inducible factor (HIF)-mediated metabolic switch is responsible for the activation of the ubiquitin-proteasome system (UPS), which precedes and is necessary for the autophagic removal of mitochondria. A defect in this pathway leads to accumulation of red blood cells (RBCs) carrying mitochondria (Mito+ RBCs) in SLE patients and in correlation with disease activity. Antibody-mediated internalization of Mito+ RBCs induces type I interferon (IFN) production through activation of cGAS in macrophages. Accordingly, SLE patients carrying both Mito+ RBCs and opsonizing antibodies display the highest levels of blood IFN-stimulated gene (ISG) signatures, a distinctive feature of SLE.

NNT-induced tumor cell "slimming" reverses the pro-carcinogenesis effect of HIF2a in tumors

BACKGROUND

HIF2a and lipid accumulation play key roles in the progression of clear cell renal cell carcinoma (ccRCC). Tumor cell "slimming" is a new concept in which tumor cells with abnormal lipids efficiently consume lipids to inhibit tumor progression without producing additional ATP. However, their respective regulatory mechanisms are still unclear. The purpose of this study is uncovering the links between these three key elements of ccRCC to elucidate new mechanisms of ccRCC metabolic abnormalities and providing a basis for new drug development for ccRCC.

METHODS

Bioinformatics screening and analyses were performed in ccRCC according to TCGA-KIRC database. qRT-PCR, luciferase reporter assay, western blot, chromatin immunoprecipitation (ChIP) assays, and other biological methods were used to explore and verify related pathways. Various cell line models and animal models were used to perform related functional experiments.

RESULTS

Screening based on sequencing data after HIF2a knockdown and three independent mitochondrial metabolism-related gene sets showed that nicotinamide nucleotide transhydrogenase (NNT) was a mediator between HIF2a and tumor cells "slimming." Further research showed that NNT had significant prognostic predictive value and was downregulated in ccRCC. It is regulated by HIF2a and can significantly activate lipid browning-mediated tumor cell "slimming." Mechanistic investigations indicated that HIF2a enhanced the expression of miR-455-5p via binding to HIF2a-related response elements in the miR-455-5p promoter, which suppresses NNT expression by binding to its 3' untranslated region.

CONCLUSIONS

Our study revealed a novel mechanism by which HIF2a decreased NNT level through a microRNA that suppressed tumor cell "slimming," resulting in the progression of ccRCC. This mechanism provides a fresh perspective of lipid accumulation in ccRCC and may help target novel strategies for the treatment of tumors with abnormal lipid metabolism.

Differential but Complementary HIF1α and HIF2α Transcriptional Regulation

Effective vascular regeneration could provide therapeutic benefit for multiple pathologies, especially in chronic peripheral artery disease (PAD) and myocardial ischemia. The hypoxia inducible factors (HIFs) mediate the cellular transcriptional response to hypoxia and regulate multiple processes that are required for angiogenesis to ultimately restore perfusion and oxygen supply. In endothelial cells, both HIF1α and HIF2α are known to contribute to this role; however, the extent and individual roles of each of these HIFα remain unclear. To characterize the individual roles of HIFα, we sequenced the transcriptional outputs of stabilized forms of HIF1α and HIF2α, where they regulated 701 and 1,454 genes, respectively. HIF1α transcription primarily regulated metabolic reprogramming, whereas HIF2α exerted a larger role in regulating angiogenic extracellular signaling, guidance cues, and extracellular matrix remodeling factors. Furthermore, HIF2α almost exclusively regulated a large and diverse subset of transcription factors and coregulators that contribute to its diverse roles in hypoxia. Further understanding of how HIFs regulate cellular processes in hypoxia and angiogenesis could offer new avenues to modulate physiological angiogenesis to enhance revascularisation in ischemic conditions and other pathologies.

Loss of vhl in the zebrafish pronephros recapitulates early stages of human clear cell renal cell carcinoma

Patients with von Hippel–Lindau (VHL) disease harbor a germline mutation in the VHL gene leading to the development of several tumor types including clear cell renal cell carcinoma (ccRCC). In addition, the VHL gene is inactivated in over 90% of sporadic ccRCC cases. ‘Clear cell’ tumors contain large, proliferating cells with ‘clear cytoplasm’, and a reduced number of cilia. VHL inactivation leads to the stabilization of hypoxia inducible factors 1a and 2a [HIF1a and HIF2a (HIF2a is also known as EPAS1)] with consequent up-regulation of specific target genes involved in cell proliferation, angiogenesis and erythropoiesis. A zebrafish model with a homozygous inactivation in the VHL gene (vhl^−/−) recapitulates several aspects of the human disease, including development of highly vascular lesions in the brain and the retina and erythrocytosis. Here, we characterize for the first time the epithelial abnormalities present in the kidney of the vhl^−/− zebrafish larvae as a first step in building a model of ccRCC in zebrafish. Our data show that the vhl^−/− zebrafish kidney is characterized by an increased tubule diameter, disorganized cilia, the dramatic formation of cytoplasmic lipid vesicles, glycogen accumulation, aberrant cell proliferation and abnormal apoptosis. This phenotype of the vhl^−/− pronephros is reminiscent of clear cell histology, indicating that the vhl^−/− mutant zebrafish might serve as a model of early stage RCC. Treatment of vhl^−/− zebrafish embryos with a small-molecule HIF2a inhibitor rescued the pronephric abnormalities, underscoring the value of the zebrafish model in drug discovery for treatment of VHL disease and ccRCC.

Summary: Zebrafish with an inactivating mutation in the vhl gene can be used as a model of early stage clear cell renal cell carcinoma, with applications for genetic studies and drug screens.

Combined epigenetic and differentiation-based treatment inhibits neuroblastoma tumor growth and links HIF2α to tumor suppression

Neuroblastoma is a pediatric cancer characterized by variable outcomes ranging from spontaneous regression to life-threatening progression. High-risk neuroblastoma patients receive myeloablative chemotherapy with hematopoietic stem-cell transplant followed by adjuvant retinoid differentiation treatment. However, the overall survival remains low; hence, there is an urgent need for alternative therapeutic approaches. One feature of high-risk neuroblastoma is the high level of DNA methylation of putative tumor suppressors. Combining the reversibility of DNA methylation with the differentiation-promoting activity of retinoic acid (RA) could provide an alternative strategy to treat high-risk neuroblastoma. Here we show that treatment with the DNA-demethylating drug 5-Aza-deoxycytidine (AZA) restores high-risk neuroblastoma sensitivity to RA. Combined systemic distribution of AZA and RA impedes tumor growth and prolongs survival. Genome-wide analysis of treated tumors reveals that this combined treatment rapidly induces a HIF2α-associated hypoxia-like transcriptional response followed by an increase in neuronal gene expression and a decrease in cell-cycle gene expression. A small-molecule inhibitor of HIF2α activity diminishes the tumor response to AZA+RA treatment, indicating that the increase in HIF2α levels is a key component in tumor response to AZA+RA. The link between increased HIF2α levels and inhibited tumor growth is reflected in large neuroblastoma patient datasets. Therein, high levels of HIF2α, but not HIF1α, significantly correlate with expression of neuronal differentiation genes and better prognosis but negatively correlate with key features of high-risk tumors, such as MYCN amplification. Thus, contrary to previous studies, our findings indicate an unanticipated tumor-suppressive role for HIF2α in neuroblastoma.