Targeting adverse effects of local prostaglandin E2 in the kidney – PROSTARGET

Renal prostaglandin E2 (PGE2) triggers renin secretion and is a key factor that controls glomerular hemodynamic. It therefore protects against hypovolemia by maintaining renal filtration. Renal PGE2 also acts on the renal tubule and vasculature to promote diuresis and natriuresis, which can worsen hypovolemia. This is best illustrated by the observation that blockers of PGE2 synthesis (nonsteroidal anti-inflammatory drugs or NSAID) can reduce renal salt or water losses observed in Bartter and Gitelman syndromes. Furthermore, the wide use of NSAID for their anti-inflammatory and analgesic properties has revealed renal side effects such as hypertension, edema and renal failure in dehydrated patients.
The present project proposes that: 1) high angiotensin II (ANGII) levels in salt-losing nephropathies account for increased medullary PGE2 production, which aims, by counteracting the vasoconstrictor effects of ANGII on the medullary vasculature, to maintain renal medullary perfusion and oxygenation. This is expected to ultimately protect the medulla from ischemic injury but at the expense of tubular dysfunction ; 2) in this settings, COX inhibitors (e.g., NSAIDs), even though they have beneficial effects on renal salt and water balance, may reduce medullary blood flow, and hence, contribute to the development of renal ischemic injury ; 3) appropriate pharmacological modulation of PGE2 action by targeting deleterious effect of PGE2 could be a new promising therapy for salt losing nephropathy.
We have generated a new mouse model of Bartter syndrome by disrupting the Clcnkb gene encoding for the basolateral Cl channel (CLC-Kb) of the distal nephron and showed that these mice exhibit a Bartter syndrome phenotype with severe renal salt and water losses and hyperprostaglandinuria. Partner 1 recently demonstrated that a murin model of type I dRTA, a disease associated with a renal salt loss, displays moderate increase in PGE2 excretion and polyuria. In this model, Na loss occurs at a post macula densa site (collecting ducts) and indomethacin normalizes sodium and water losses. These models are thus valuable tools to dissect the dual role of PGE2 in the pathophysiology of salt-losing tubulopathies in order to identify targets for new therapeutic strategies.
The overall goals of our consortium are : 1) identify the deleterious and beneficial effects of PGE2 in salt losing tubulopathies; 2) identify high renal expression sites of the key enzymes for PGE2 synthesis and thereby potential targets for PGE2 action; 3) assess the effects of targeted inhibition of PGE2 synthesis and selective prostaglandin receptors inactivation on renal hemodynamic, Na and water balance and renal injury; 4) demonstrate that ANGII through AT1a receptor activation of medullary interstitial cells or collecting duct cells leads to PGE2 synthesis and prevents medulla from ischemia and fibrosis.
The implementation of the objectives of the project relies on the use of new cutting edge techniques together with "old but direct" functional techniques that have proved to be highly efficient for obtaining straightforward demonstration of physiological and pathophysiological mechanisms. This project combines several complementary experimental approaches: generation of genetically modified mouse models, in vivo physiological analyses (metabolic cages for urine analyses, renal hemodynamic including measurement of arterial blood pressure by radio-telemetry and glomerular filtration rate), protein and gene expression analyses on kidney and isolated renal structures, renal histology and immunohistochemistry. This grant application builds upon the complementary expertise of two partners: Partner 1 has has has long-lasting expertise in kidney phenotyping of genetic mouse models, and immunohistochemical and immunoblot analyses of renal proteins. Partner 2 is an expert on renal histology and physiology, and high throughput screening techniques on tubules sorted by FACS.