| Popis: |
The beta-adrenergic receptor (bAR) exists in an equilibrium of inactive and active conformational states, which is modulated by ligands resulting in downstream signaling. In addition to cAMP, bAR regulates hypoxia-inducible factor 1 (HIF-1). We hypothesized that HIF-1 signaling occurs via a unique, independent bAR conformation and that Pulmonary Arterial Hypertension (PAH) patients with HIF-biased conformations would have blunted cAMP response. We found isoproterenol and salbutamol, both cAMP agonists, had opposing effects on HIF-1 in cells and mice. Additionally, hypoxia blunted agonist-stimulated cAMP in vitro, consistent with receptor equilibrium shifting towards HIF-activating conformations. bAR overexpression in cells increased HIF-1 activity and glycolysis which was blunted by HIF-1 inhibitors, suggesting increased bAR increases basal HIF-1 signaling. Because PAH is also characterized by HIF-related glycolytic shift, we dichotomized PAH patients in the PAHTCH trial (NCT01586156) based on right ventricular glucose uptake to evaluate bAR signaling. Patients with high glucose uptake had more severe disease than those with low uptake and had no response to bAR ligands. The findings expand the paradigm of bAR regulation and uncover a novel PAH subtype that might benefit from b-blockers. Circulating cell-free mitochondrial components are well characterized as mediators of inflammation. Recent studies show cells also release microparticles (MPs) containing intact mitochondria under conditions of stress or injury. However, detection of cell-free mitochondria and their cellular origin has not been studied in non-pathological conditions. Thus, we hypothesize that intact mitochondria are detectable in the circulation under physiological conditions. To test this, plasma MPs were analyzed via flow cytometry. Murine platelet-depleted plasma showed a small cluster of MPs which was 65% positive for the mitochondrial marker MitoTracker Green (MT Green). Additionally, transgenic mice expressing mitochondrial GFP had GFP positive MPs in their plasma. Human plasma also contained cell-free mitochondria, with approximately 11% of the total MPs staining MT green positive. Platelets and endothelial cells were sources of MT green positive MPs in mice and humans, based on cell-specific surface markers. Leukocytes were also a source of mitochondria in humans but not mice. Together these data show multiple cell types release intact mitochondria into the circulation in healthy individuals. |
