Although hypoxia drives chronic kidney disease (CKD) and promotes end stage renal disease, the mechanisms underlying the pathogenesis of renal hypoxia and disease progression are poorly understood. Thus, the goal of proposed research is to identify distinct signals and networks underlying renal hypoxia and establish novel approaches to increase kidney oxygenation and prevent disease progression. The erythrocyte is the most abundant cell type in our body, acting as both a deliverer and sensor of oxygen (O2). However, their role in increasing renal oxygenation to slow disease progression in CKD remain unknown. The proposed research builds on our unbiased high throughput metabolomics screening and mouse genetic studies showing that plasma adenosine and erythrocyte sphingosine 1-phosphate (S1P) are elevated in humans ascending to high altitude and that these two metabolites work together to induce 2,3-bisphosphoglycerate (2,3-BPG), an erythrocyte specific allosteric modulator that decreases hemoglobin-O2 binding affinity, and thus increases O2 delivery to counteract hypoxic tissue damage in mice. Significantly, increased erythrocyte 2,3-BPG and the O2 delivery are also observed in CKD patients and associated with disease severity. Follow-up mouse genetic studies demonstrated that activation of the erythrocyte A2B adenosine receptor (ADORA2B) induces 2,3-BPG production and enhances O2 delivery that has a general protective role to counteract renal hypoxia, damage and disease progression in two independent experimental models of CKD. Mechanistically, we discovered that AMPK, a cellular master energy sensor, functions downstream of ADORA2B underlying adenosine induced-2,3-BPG production and O2 delivery. Moreover, we revealed that elevated sphingosine kinase I (SphK1) also functions downstream of ADORA2B contributing to hypoxia-induced S1P production and that increased intracellular S1P directly binds Hb and promotes erythrocyte hypoxic metabolic reprogramming to induce 2,3-BPG production and O2 delivery and thus counteract renal hypoxia. Overall, our recent findings support the intriguing hypotheses that erythrocyte hypoxic metabolic reprogramming mediated by adenosine-ADORA2B-AMPK and SphK1-S1P signaling networks has a beneficial role to lower renal hypoxia and slow disease progression by inducing 2,3- BPG production and O2 delivery. To test these hypotheses, AIM I and II include multiple novel genetic tools coupled with multidisciplinary unbiased, robust and state of art techniques including proteomic, metabolomics, RNA deep sequencing and isotopically labelled glucose flux to determine how ADORA2B-AMPK and S1P- mediated erythrocyte hypoxic metabolic reprogramming protects renal hypoxia and disease progression in CKD.
In AIM III, we will conduct preclinical studies to test the therapeutic effects of multiple FDA approved drugs to enhance our newly identified erythrocyte signaling pathways in CKD. Overall, the proposed research has interrelated goals to translate our findings into innovative therapeutics for CKD by providing new molecular insight into ?erythrocyte metabolic hypoxia reprogramming? in CKD and disease progression.
Hypoxia is defined as an inadequate O2 supply to whole body or a region of body. Hypoxia is a dangerous condition for both normal individuals under high altitude hypoxia and patients with chronic renal disease, respiratory and hemolytic diseases. However, current strategies to counteract physiological and pathological hypoxia are limited due to a lack of fundamental understanding of the molecular mechanisms underlying adaptation to hypoxia. Research proposed here is based on our novel and compelling findings revealing that plasma adenosine are elevated to promote erythrocyte metabolic changes and trigger oxygen delivery to adapt to high altitude and counteract renal hypoxia, kidney damage and disease progression in chronic kidney disease (CKD). The proposed studies are extremely innovative since the functional role of adenosine mediated-oxygen delivery from red blood cells in CKD had not been previously recognized. The impact of proposed research is highly significant since it is likely to provide innovative therapies in CKD and even in any condition involving hypoxia.
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