Vertical sleeve gastrectomy increases duodenal Lactobacillus spp. richness associated with the activation of intestinal HIF2α signaling and metabolic benefits

OBJECTIVE

Vertical Sleeve Gastrectomy (VSG) is one of the most efficacious treatments for obesity and its comorbidities. Although a range of evidence suggests that alterations of the microbiota in the distal gut following VSG are pivotal to these metabolic improvements, the effect of surgery to alter the microbiota of the proximal intestine and its effect on host physiology remain largely unknown. As the main bacteria in the upper small intestine, Lactobacillus subspecies have been appreciated as important regulators of gut function. These bacteria also regulate intestinal Hypoxia- Inducible Factor 2α (HIF2α) signaling that plays an integral role in gut physiology and iron absorption. In the present study, we sought to determine the impact of VSG on Lactobacillus spp. in the small intestine and potential downstream impacts of Lactobacillus spp. on HIF2α, specifically in the duodenum.

METHODS

To determine the effects of VSG on the microbiota and HIF2α signaling in the duodenum, VSG surgeries were performed on diet-induced obese mice. To further probe the relationship between Lactobacillus spp. and HIF2α signaling in the duodenum, we applied a customized high-fat but iron-deficient diet on mice to increase duodenal HIF2α signaling and determined alterations of gut bacteria. To explore the causal role of Lactobacillus spp. in duodenal HIF2α signaling activation, we chronically administered probiotics containing Lactobacillus spp. to high-fat-fed obese mice. Lastly, we studied the effect of lactate, the major metabolite of Lactobacilli, on HIF2α in ex vivo duodenal organoids.

RESULTS

There were pronounced increases in the abundance of Lactobacillus spp. in samples isolated from duodenal epithelium in VSG-operated mice as compared to sham-operated mice. This was accompanied by an increase in the expression of genes that are targets of HIF2α in the duodenum of VSG-treated mice. Activating HIF2α signaling with a high-fat but iron-deficient diet resulted in weight loss, improvements in glucose regulation, and increased Lactobacillus spp. richness in the duodenum as compared to mice on an iron-replete diet. Chronic administration of probiotics containing Lactobacillus spp. not only increased HIF2α signaling in the duodenum such as occurs after VSG but also resulted in reduced weight gain and improved glucose tolerance in high-fat-fed mice. Furthermore, lactate was able to activate HIF2α in ex vivo duodenal organoids.

CONCLUSIONS

These results support a model whereby VSG increases duodenal Lactobacillus richness and potentially stimulates intestinal HIF2α signaling via increased lactate production.

Transforming growth factor-β1 decreases erythropoietin production through repressing hypoxia-inducible factor 2α in erythropoietin-producing cells

BACKGROUND

Renal erythropoietin (EPO)-producing (REP) cells produce EPO through hypoxia-inducible factor (HIF) 2α-activated gene transcription. Insufficient EPO production leads to anemia in patients with chronic kidney disease. Although recombinant EPO is effective to improve anemia, no reliable REP cell lines limit further progress of research and development of novel treatment.

METHODS

We screened Epo mRNA expression in mouse fibroblast cell lines. Small interfering RNA specific for HIF1α or HIF2α was transfected to study Epo expression in C3H10T1/2 cells. The effect of transforming growth factor-β1 (TGF-β1) on HIF-EPO axis was studied in C3H10T1/2 cells and mice.

RESULTS

Similar to mouse REP pericytes, C3H10T1/2 cells differentiated to α-smooth muscle actin⁺ myofibroblasts after exposure to TGF-β1. Specific HIF knockdown demonstrated the role of HIF2α in hypoxia-induced Epo expression. Sustained TGF-β1 exposure increased neither DNA methyltransferase nor methylation of Epas1 and Epo genes. However, TGF-β1 repressed HIF2α-encoding Epas1 promptly through activating activin receptor-like kinase-5 (ALK5), thereby decreasing Epo induction by hypoxia and prolyl hydroxylase domain inhibitor roxadustat. In mice with pro-fibrotic injury induced by ureteral obstruction, upregulation of Tgfb1 was accompanied with downregulation of Epas1 and Epo in injured kidneys and myofibroblasts, which were reversed by ALK5 inhibitor SB431542.

CONCLUSION

C3H10T1/2 cells possessed the property of HIF2α-dependent Epo expression in REP pericytes. TGF-β1 induced not only the transition to myofibroblasts but also a repressive effect on Epas1-Epo axis in C3H10T1/2 cells. The repressive effect of TGF-β1 on Epas1-Epo axis was confirmed in REP pericytes in vivo. Inhibition of TGF-β1-ALK5 signaling might provide a novel treatment to rescue EPO expression in REP pericytes of injured kidney.

The HIF-2α/PPARα pathway is essential for liraglutide-alleviated, lipid-induced hepatic steatosis

Liraglutide has been demonstrated to alleviate hepatic steatosis in clinical practice, but the underlying mechanism remains unclear. Our previous study indicated that the HIF-2α/PPARα pathway was involved in hepatic lipid accumulation induced by hypoxia.We aimed to investigate whether liraglutide could alleviate lipid-induced hepatic steatosis via the HIF-2α/PPARα pathway. Whole-body HIF-2α heterozygous knockout (HIF-2α^+/-) mice and littermate wild-type (WT) mice were successfully established. Male mice challenged with a high-fat diet were treated with liraglutide (0.6 mg/kg/d) or normal saline by intraperitoneal injection for 4 weeks. We observed that, compared with WT mice, many indicators of HIF-2α^+/- mice improved, including GTT, ITT, fasting blood glucose, body weight, liver weight, and lipid profile in serum or liver lipid deposition, and the expression level of PPARα, mitochondrial function genes, and fatty acid oxidation genes were upregulated, while those of HIF-2α and lipogenesis genes were downregulated significantly. After liraglutide treatment in WT mice, we found that significant improvements were observed in the fat mass, GTT, ITT, fasting blood glucose, body weight, liver weight, lipid profile in serum or liver lipid deposition; the β-oxidation genes were upregulated and the lipogenesis genes were downregulated; and the abundance of intestinal Akkermansia muciniphila increased significantly. However, the effects of liraglutide on WT mice were not observed in HIF-2α^+/- mice. In addition, in the HepG2 steatotic hepatocyte model, liraglutide alleviated lipid deposits by repressing lipid synthesis and enhancing fatty acid β-oxidation, which were substantially suppressed by the HIF-2α modulators. Therefore, the HIF-2α/PPARα pathway is essential for liraglutide-alleviated lipid-induced hepatic steatosis.

Tumor infiltrating mast cells determine oncogenic HIF-2α-conferred immune evasion in clear cell renal cell carcinoma

PURPOSE

Hypoxia-inducible factor 2α (HIF-2α) overexpression leads to activation of angiogenic pathways. However, little is known about the association between HIF-2α expression and anti-tumor immunity in clear cell renal cell carcinoma (ccRCC). We aimed to explore how HIF-2α influenced the microenvironment and the underlying mechanisms.

EXPERIMENTAL DESIGN

We immunohistochemically evaluated immune cells infiltrations and prognostic value of HIF-2α expression in a retrospective Zhongshan Hospital cohort of 280 ccRCC patients. Fresh tumor samples, non-tumor tissues and autologous peripheral blood for RT-PCR, ELISA and flow cytometry analyses were collected from patients who underwent nephrectomy in Zhongshan Hospital from September 2017 to April 2018. The TCGA KIRC cohort and SATO cohort were assessed to support our findings.

RESULTS

We demonstrated that ccRCC patients with HIF-2αhigh tumors exhibited reduced overall survival (p = 0.025) and recurrence-free survival (p < 0.001). Functions of CD8+ T cells were impaired in HIF-2αhigh patients. In ccRCC patients, HIF-2α induced the expression of stem cell factor (SCF), which served as chemoattractant for mast cells. Tumor infiltrating mast cells impaired anti-tumor immunity partly by secreting IL-10 and TGF-β. HIF-2α mRNA level adversely associated with immunostimulatory genes expression in KIRC and SATO cohorts.

CONCLUSIONS

HIF-2α contributed to evasion of anti-tumor immunity via SCF secretion and subsequent recruitment of mast cells in ccRCC patients.

Combined over-expression of the hypoxia-inducible factor 2α gene and its long non-coding RNA predicts unfavorable prognosis of patients with osteosarcoma

BACKGROUND

LncRNA hypoxia-inducible factor-2α (HIF-2α) promoter upstream transcript (HIF2PUT) functions as a novel regulatory factor of osteosarcoma stem cells partly by controlling HIF-2α expression. The aim of this study was to investigate the clinical significance of HIF-2α and HIF2PUT in human osteosarcoma.

MATERIALS AND METHODS

Quantitative real-time PCR was performed to detect the expression levels of HIF-2α mRNA and HIF2PUT in 82 surgical specimens of primary osteosarcoma and matched non-cancerous bone tissues. Then, the associations of HIF-2α and/or HIF2PUT expression with various clinicopathological features of osteosarcoma patients were statistically analyzed. Moreover, their prognostic value was further evaluated.

RESULTS

Compared with non-cancerous bone tissues, HIF-2α mRNA and HIF2PUT expression were both significantly upregulated in osteosarcoma tissues (all P<0.001). Interestingly, the expression levels of HIF-2α mRNA in osteosarcoma tissues were positively correlated with those of HIF2PUT (r=0.28, P=0.009). Additionally, osteosarcoma patients with HIF-2α mRNA and/or HIF2PUT over-expression more frequently had large tumor size (all P<0.05), advanced clinical stage (all P<0.01) and positive distant metastasis (all P<0.01). Moreover, osteosarcoma patients with HIF-2α mRNA and/or HIF2PUT over-expression had a significantly shorter overall and disease-free survival (all P<0.05). Furthermore, Cox multivariate analysis identified that HIF-2α mRNA and/or HIF2PUT expression, clinical stage and distant metastasis were all independent and significant prognostic factors for both overall and disease-free survival (all P<0.05).

CONCLUSIONS

HIF-2α and HIF2PUT upregulation may be a common feature in human osteosarcomas with aggressive potency. The over-expression of the two molecules, alone or combined, may predict poor prognosis in osteosarcoma patients.

Somatic gain-of-function HIF2A mutations in sporadic central nervous system hemangioblastomas

Central nervous system hemangioblastomas (CNS-HBs) occur sporadically or as a component of von Hippel-Lindau-VHL syndrome. CNS-HBs share some molecular similarities with pheochromocytomas/paragangliomas (PPGLs) and renal cell carcinomas (RCCs). Recently, hypoxia-inducible factors, particularly somatic HIF2A mutations, have been found to play an important role in the pathogenesis of PPGLs. Somatic mutations in HIF2A have been reported in PPGLs associated with polycythemia, which have been reported to also be present in patients with RCCs and HBs. However, whether CNS-HBs is associated with the presence of a HIF2A mutation is currently uknown. We analyzed somatic HIF2A and VHL mutations in a series of 28 sporadic CNS-HBs. We also investigated the expression of HIF target proteins and hypoxia-associated factor (HAF). Two sporadic CNS-HBs were found to have somatic HIF2A mutations. One tumor had 2 HIF2A missense mutations, one of which was previously described in a PPGL (c.1121 T>A, F374Y). The second patient had coexistence of somatic truncated mutations (c.1669 C>T, Q557*) in HIF2A together with a VHL mutation. Neither of the two patients had polycythemia at the time of diagnosis. We demonstrate that the novel truncated mutation in HIF2A (Q557*) affects HIF-2α prolyl hydroxylation with its reduced ubiquitination but intact transcriptional activity, resulting in an activating effect. Both CNS-HB samples showed positive expression of VEGFR2/CA9/Glut1 and HAF. Our data support the unique central role of the VHL/HIF-2α signaling pathway in the molecular pathogenesis of CNS-HBs and show for the first time the presence of HIF2A mutations in sporadic HB.