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Targeting HIF-2α in skeletal progenitors and their descendants for the radioprotection of bone

ABSTRACT: Radiotherapy continues to be a common treatment modality for cancer despite skeletal complications. Currently, there are no effective treatments for radiation-induced bone loss. Radiation induces substantial changes to the bone microenvironment; however, the effects of these changes on skeletal progenitors and their descendants remain elusive. Following radiation, LeprCre skeletal progenitors and their descendants, localize to hypoxic regions and exhibit HIF-2α stabilization, thus implicating a role for HIF-2α in radiation-induced bone loss. To test whether HIF-2α deficiency rescues radiation-induced bone loss, we conditionally ablated HIF-2α in LeprCre-expressing cells and their descendants. Compared to irradiated controls, irradiated LeprCre;Hif-2αfl/fl knock out mice demonstrate increased bone mass with values comparable to non-irradiated animals. Mechanistically, HIF-2α negatively regulates osteoblastogenesis, mineralization, and number of skeletal progenitors. To test whether HIF-2α can be targeted therapeutically, we administered PT2399, a potent and selective HIF-2α inhibitor whose structural analog belzutifan, has recently received FDA approval. Administration of PT2399 was sufficient to prevent radiation-induced bone loss in a single-limb irradiation model. As ~90% of patients on HIF-2α inhibitor treatment develop anemia, we constructed a PT2399-loaded bone-targeting nanocarrier (Aln-PT-NC) to increase on-target efficacy and reduce off-target kidney toxicity. Delivery of Aln-PT-NC completely prevented radiation-induced bone loss while reducing drug accumulation in the kidney. In this study, we identify HIF-2α as a negative regulator of bone formation in LeprCre skeletal progenitors and their descendants following radiotherapy and developed a bone-targeting HIF-2α therapeutic. Together, these studies highlight the clinical potential of Aln-PT-NC to be translated into a treatment regimen for bone radioprotection.

ORGANISM(S): Mus musculus

PROVIDER: GSE235292 | GEO | 2023/06/24

REPOSITORIES: GEO

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Project description:To investigate the detailed molecular mechanisms for the regulatory role of HIF-2α in experimental colitis, microarray gene expression analysis was performed on colon RNA isolated from 6- to 8-week-old Hif-2αF/F, Hif-2αlΔIE mice treated with 3%DSS for 3 days. Background & Aims: Hypoxic inflammation is characterized by decreased oxygen tension in inflammatory foci, and is a notable feature in inflammatory bowel disease (IBD). Hypoxic response is mediated by transcription factors hypoxia-inducible factor (HIF)-1α and HIF-2α, both of which are highly induced in IBD. HIF-1α is a protective factor that limits intestinal barrier dysfunction during inflammation. However, the role of HIF-2α has not been assessed in hypoxic inflammation and IBD. Methods: A hypoxia reporter mouse model was used to test the presence of hypoxia and HIF-2α in dextran sulfate sodium (DSS) and Citrobacter rodentium (C.rod)-induced colitis. The role of HIF-2α in these mouse models of colitis was further assessed in mice with an intestinal epithelium-specific gain- and loss-of-function of HIF-2α. Results: Induction of hypoxia and HIF-2α was confirmed in both murine experimental colitis models and human IBD samples. Disruption of HIF-2α attenuated colonic inflammation whereas stabilization of HIF-2α potentiated inflammation in mouse models of colitis. Interestingly, intestine specific overexpression of HIF-2α but not HIF-1α leads to spontaneous colitis and premature death in mice. Further mechanistic analysis showed that HIF-2α is a driver for pro-inflammatory response and is critical regulator of intestinal epithelial-derived tumor necrosis factor (TNF)-α. Blocking TNF-α completely ameliorated HIF-2α potentiated intestinal inflammation. Conclusions: These data demonstrate that HIF-2α is a critical transcription factor essential in intestinal epithelium elicited inflammatory response. Global gene expression profiling in colon RNAs isolated from 7-week-old Hif-2αF/F (n=6, Shah 007) and Hif-2αΔIE (n=5, Shah 008).

Project description:To identify the precise molecular mechanisms that could contribute to the increase in colon carcinogenesis, microarray gene expression analysis was performed on colon RNA isolated from 5-week-old VhlF/F and VhlΔIE, VhlΔIE/Apcmin/+ and VhlF/F/Apcmin/+ mice. Hypoxia-inducible factor (HIF) is a key modulator of the transcriptional response to hypoxia and is increased in colon cancer. However, the role of HIF in colon carcinogenesis in vivo remains unclear. Intestinal epithelium-specific disruption of the von Hippel-Lindau tumor suppressor protein (VHL) resulted in constitutive HIF signaling, and increased HIF expression augmented colon tumorigenesis in the Apcmin/+ intestinal tumor model. Intestine-specific disruption of Vhl increased colon tumor multiplicity and progression from adenomas to carcinomas. These effects were ameliorated in mice with double disruption of Vhl and Hif-2α. Activation of HIF signaling resulted in increased cell survival in normal colon tissue, however tumor apoptosis was not affected. Interestingly, a robust activation of cyclin D1 was observed in tumors of Apcmin/+ mice in which HIF-2α was activated in the intestine. Consistent with this result, BrdU incorporation indicated that cellular proliferation was increased in colon tumors following HIF activation. Further analysis demonstrated that dysregulation of the intestinal iron absorption transporter divalent metal transporter-1 (DMT-1) was a critical event in HIF-2α-mediated colon carcinogenesis. These data provide a mechanistic basis for the widely reported link between iron accumulation and colon cancer risk. Together, our findings demonstrate that a chronic increase in HIF-2α in the colon initiates pro-tumorigenic signaling which may have important implications in developing preventive and therapeutic strategies for colon cancer. Global gene expression profiling in colon RNAs isolated from 5-week-old VhlF/F (n=4, Shah 001), VhlF/F/Apcmin/+(n=3, Shah 003), VhlΔIE (n=3, Shah 002) and VhlΔIE/Apcmin/+ mice (n=5, Shah 004).

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Targeting HIF-2α in skeletal progenitors and their descendants for the radioprotection of bone

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