Research Interests
In 2004, while pursuing a study on the role of angiotensin and receptor mediated regulation of membrane transport, we made a discovery that has since driven my research program. We found that mast cells express and secrete renin, the rate-limiting enzyme in the renin-angiotensin system cascade. While others had demonstrated renin mRNA in numerous cell types, we were the first to identify an extra-renal source of this aspartyl protease. Mast cell renin is active and can trigger the local production of angiotensin. In that all organs have a resident population of mast cells, our finding favors the concept that angiotensin can be made in an organ when mast cells degranulate without invoking the traditional renin-angiotensin system axis.
Angiotensin II (ANG II) plays a homeostatic role in preserving normal circulation and tissue perfusion. However if it is elevated systemically it leads to vasoconstriction and hypertension. At the tissue level, angiotensin is pro-fibrotic, pro-inflammatory, and vasoactive. My research efforts explore a new paradigm founded on our tenet that tissue mast cells release renin which drives the local production of angiotensin. We are presently investigating the role of mast cell renin and local angiotensin formation in renal fibrosis, diabetes and cardiac arrhythmias.
Renal Fibrosis: Progressive kidney disease is characterized by the accumulation of fibrotic mediators in the kidney. Glomerulonephritis, diabetic nephropathy, pyelonephritis, and renovascular disease together account for over 75% of patients requiring renal transplants. In these conditions it is chronic progressive renal fibrosis with associated loss of functioning nephrons that results in irreversible renal injury. While the renin angiotensin system (RAS) has traditionally been viewed as a circulating axis, evidence is accumulating that an active intrarenal RAS plays an important role in chronic kidney disease and fibrosis. Based on recent evidence reported from our lab that mast cells express and release active renin, we hypothesize that renin released from mast cells infiltrating the kidney triggers intra-renal RAS and local angiotensin (ANG II) formation. The overall objective of this proposal is addressing the important issue of whether infiltrating mast cells and mast-cell renin, play a significant role in ischemic organ damage and fibrosis. Using a model of progressive renal fibrosis (unilateral ureteral obstruction (UUO)) we will study the role of mast cell renin and local ANG II production in this process as well as investigate the role of adenosine in regulating mast cell renin gene expression. Our preliminary results demonstrate: 1. Human and rodent kidney mast cells express active renin. 2. Mast cell deficient mice do not develop renal fibrosis with UUO 3. Stabilizing mast cells in rat UUO kidney prevents renal fibrosis. 4. Inhibiting the renin released from mast cells reduces vasoconstriction in isolated and perfused kidney. 5. Stimulating the adenosine A2b receptor increases mast cell renin gene expression. In Specific Aim I. we will characterize the molecular identity of mast cell renin and examine the effects of mast cell renin and local ANG II formation on fibrosis and vasoconstriction in UUO. These experiments will be done with mast cells isolated from human and rodent kidney and with HMC-1 cells, a cultured cell model of human mast cells. The UUO animal studies will be carried out in rat and mast cell-deficient c-Kit knockout mice and their congenic controls. Specific Aim II. will examine regulation of mast cell renin expression, synthesis, and release by adenosine. These experiments will be done with isolated human kidney mast cells and with HMC-1 cells. If our hypothesis is proven correct then we will have identified a novel therapeutic target (mast cell renin) for ameliorating renal function in chronic kidney disease.
Diabetes: Inhibition of the renin-angiotensin system (RAS) has become a key factor in cardiovascular and renal medicine. Angiotensin II (ANG II) plays a homeostatic role in preserving normal circulation and tissue perfusion; yet inhibition of RAS components in the diabetic can attenuate early onset nephropathy and retinopathy even in the absence of an elevated active plasma RAS. This suggests that RAS is activated at the local organ level. The start of microvascular disease in the patient with diabetes, both nephropathy and retinopathy, occurs early and is probably due to local endogenous vasoactive substances. Based on recent evidence reported from our lab that mast cells express and release active renin, we hypothesize that tissue RAS and the ensuing ANG II is responsible for changes in the microcirculation related to diabetic nephropathy and retinopathy. The overall objective of this proposal is addressing the important issue of whether infiltrating mast cells and mast-cell renin, the rate limiting enzyme in the RAS cascade, play a significant role in abnormalities of the microcirculation associated with diabetes. Our preliminary results demonstrate: 1. Human kidney mast cells (normal connective tissue) and infiltrating mast cells in human diabetic kidney express renin; 2. Stabilizing mast cells in streptozotocin (stz)- induced diabetic rats reduces renal fibrosis; 3. Inhibiting the renin released from mast cells reduces the vasoconstriction and vascular resistance in isolated and perfused kidney from stz-rat; 4. Stz-induced diabetic rats express renin-positive mast cells in the retina/vitreous, areas associated with retinopathy; 5. Topical adminsitration of mast cell stabilizer to eyes of stz-induced diabetic rats reduces capillary leakage and maintains the integrity of the retinal capillary bed. In Specific Aim I. we will characterize mast cell renin and study its regulation by adenosine in cultured human mast cells (HMC-1) and native mast cells isolated from kidney (rodent and human). Using stz-induced diabetic rats and mast-cell-deficient mice, experiments proposed in Specific Aim II. will study the pathological implications of mast cell renin release and local ANG II formation on renal vasoconstriction, norepinephrine release, and fibrosis; and injury to the retinal vasculature. If proven correct we will have identified a novel therapeutic target (mast cells and mast cell renin) for ameliorating diabetic end stage renal disease and blindness.
Cardiac Arrthymias: Having identified renin in cardiac mast cells, we assessed whether its release leads to cardiac dysfunction. In Langendorff-perfused guinea pig hearts, mast cell degranulation with compound 48/80 released Angiotensin I - forming activity. This activity was blocked by the selective renin inhibitor BILA2157, indicating that renin was responsible for Angiotensin I formation. Local generation of cardiac Ang II from mast cell–derived renin also elicited norepinephrine release from isolated sympathetic nerve terminals. This action was mediated by Angiotensin II-type 1 (AT1) receptors. In 2 models of ischemia/reperfusion using Langendorff-perfused guinea pig and mouse hearts, a significant coronary spillover of renin and norepinephrine was observed. In both models, this was accompanied by ventricular fibrillation. Mast cell stabilization with cromolyn or lodoxamide markedly reduced active renin overflow and attenuated both norepinephrine release and arrhythmias. Similar cardioprotection was observed in guinea pig hearts treated with BILA2157 or the AT1 receptor antagonist EXP3174. Renin overflow and arrhythmias in ischemia/reperfusion were much less prominent in hearts of mast cell–deficient mice than in control hearts. Thus, mast cell–derived renin is pivotal for activating a cardiac renin-angiotensin system leading to excessive norepinephrine release in ischemia/reperfusion. Mast cell–derived renin may be a useful therapeutic target for hyperadrenergic dysfunctions, such as arrhythmias, sudden cardiac death, myocardial ischemia, and congestive heart failure. Work continues on the role of mast cells renin and a cardiac renin-angiotensin system. This work is being pursued with my collaborator, Dr. Roberto Levi, Department of Pharmacology.
