Hypoxia-Inducible Factor in Hereditary Hemorrhagic Telangiectasia

• Applicants: Privatdozentin Dr. Freya Dröge; Dr. Anna Wrobeln
• Subject Area: Otolaryngology, Phoniatrics and Audiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540544506

Hereditary hemorrhagic telangiectasia (HHT) affects ~ 85,000 people in Europe. Various mutations in genes within the transforming growth factor-β (TGF-β) signaling pathway cause pathological dilation of blood vessels in HHT. These telangiectasias in liver, lungs, intestine and brain cause life-threatening hemorrhages. Because TGF-β regulates the immune response, HHT patients suffer from infections and an increased risk of sepsis, the leading cause of death in these patients. TGF-β and hypoxia-inducible factors (HIF) are both required for the activation of the immune response. We previously showed that HHT leukocytes have a significantly reduced HIF1A gene, HIF target gene, and HIF-1α protein expression, suggesting a disturbed HIF regulation in HHT. The aim of this project is to determine whether the reduced accumulation of HIF-1α protein is responsible for the immune deficiency in HHT patients and if it is possible to restore the immune system by pharmacological stabilization of HIF-1α. We propose a 36-month project divided into three work packages. (I) HIF-1α suppression in HHT leukocyte subtypes: We will sort the patient’s leukocyte for relevant subtypes and analyze its HIF-1α expression. Furthermore, we will stabilize HIF-1α by hypoxic or pharmacological inhibition of its regulatory enzymes. This stabilization may lead to the restoration of the physiological function of immune cells by stabilizing HIF-1α as quantified by measuring cytokine release. (II) Effect of HIF-1α suppression on metabolic function in HHT leukocytes: HIF is a critical metabolic mediator that ensures the proper functioning of leukocytes in situations of increased energy demand. Following inflammatory stimulation, several leukocytes undergo a switch from aerobic mitochondrial respiration to anaerobic glycolysis (glycolytic switch). This switch is HIF-1α dependent. The observed immunodeficiency in HHT patients may be due to an impaired metabolic function and inability to perform a glycolytic switch during activation. We will test whether pharmacological stabilization of HIF-1α leads to restoration of the metabolic function of HHT leukocytes. Metabolic flux analysis (Seahorse) and Fluorescence Activated Cell Sorting of HHT leukocytes will link the potentially impaired glycolytic switch to the lack of immune cell activation. (III) Inflammation in HHT mice with and without HIF stabilization: The analysis of leukocytes in their physiological environment will provide solid information about HIF as a therapeutic target in HHT patients. HHT mice with acute colon inflammation will be treated with the FDA approved HIF stabilizer Roxadustat. The immune response should be restorable due to HIF-1α stabilization in HHT mice, as indicated by a milder course of inflammation. Hypothesis: Loss of HIF-1α in HHT causes an impaired immune response. We aim to validate this hypothesis using a functional approach by targeting HIF stabilization as a new pharmacological strategy in HHT.

• DFG Programme: Research Grants