| Summary: |
The current project evolved from several research lines that have been pursued in the lab regarding the physiological aspects of sodium retention and edema formation in nephrotic syndrome (NS), more specifically the role of the renal dopaminergic system (RDS). The aim of this project is to investigate the interaction between the deficiency of RDS in NS which was described by our group (1,2,3) and the dysfunction of the natriuretic peptide system (NPS) which is well recognized in NS. Moreover, we will study the possible contribution of vitamin D3 deficiency in the NS, not only to the dysfunction of NPS but also to the cardiac remodeling and dysfunction in NS which was also recently described by our group (4). In addition to the above mentioned studies, the present project is based on the following observations: a) the natriuretic response to ANP requires an intact RDS and it is well recognized a synergistic effect between RDS and NPS (5); b) Vitamin D3 can activate the NPS, namely in the inner medullary collecting ducts (6); c) vitamin D3 is endowed with potential cardioprotective effects (13,27).The potential relevance of this project is related with the fact that the mechanisms that can explain the enhanced sodium retention and increased cardiovascular risk in NS are far from being disclosed. Namely, the interaction between the activities of NPS and RDS as well as the role of vitamin D3 deficiency was not previously addressed in NS. The following study protocols are planed using the NS rat model induced by puromycin aminonucleoside (NS-PAN): A. Dopamine 1 receptor (D1R) expression in renal tubules will be evaluated in the renal cortex and medulla at 7, 14, and 21 days after PAN administration. We have previously reported a blunted RDS activity in PAN-NS, evidenced by reduced urinary excretion of dopamine (DA) and metabolites, going along with decreased DA synthesis in renal tubules and blunted natriuretic response to D1R agonists (1). B. Evaluation of the intera  |
Summary
The current project evolved from several research lines that have been pursued in the lab regarding the physiological aspects of sodium retention and edema formation in nephrotic syndrome (NS), more specifically the role of the renal dopaminergic system (RDS). The aim of this project is to investigate the interaction between the deficiency of RDS in NS which was described by our group (1,2,3) and the dysfunction of the natriuretic peptide system (NPS) which is well recognized in NS. Moreover, we will study the possible contribution of vitamin D3 deficiency in the NS, not only to the dysfunction of NPS but also to the cardiac remodeling and dysfunction in NS which was also recently described by our group (4). In addition to the above mentioned studies, the present project is based on the following observations: a) the natriuretic response to ANP requires an intact RDS and it is well recognized a synergistic effect between RDS and NPS (5); b) Vitamin D3 can activate the NPS, namely in the inner medullary collecting ducts (6); c) vitamin D3 is endowed with potential cardioprotective effects (13,27).The potential relevance of this project is related with the fact that the mechanisms that can explain the enhanced sodium retention and increased cardiovascular risk in NS are far from being disclosed. Namely, the interaction between the activities of NPS and RDS as well as the role of vitamin D3 deficiency was not previously addressed in NS. The following study protocols are planed using the NS rat model induced by puromycin aminonucleoside (NS-PAN): A. Dopamine 1 receptor (D1R) expression in renal tubules will be evaluated in the renal cortex and medulla at 7, 14, and 21 days after PAN administration. We have previously reported a blunted RDS activity in PAN-NS, evidenced by reduced urinary excretion of dopamine (DA) and metabolites, going along with decreased DA synthesis in renal tubules and blunted natriuretic response to D1R agonists (1). B. Evaluation of the interaction between the NPS dysfunction and blunted RDS activity in NS. Seven days after PAN administration, the effects of the PDE5 inhibitor (zaprinast) will be assessed on: a. Renal function, proteinuria and sodium balance; b. urinary excretion of DA, its precursor (L-DOPA) and metabolites (DOPAC, 3-MT and HVA); c. cGMP urinary excretion; d. expression and cellular distribution of D1R in renal tubules e. DARPP-32 protein expression; f. cAMP tissue levels in renal cortex and medulla. The dysfunction of NPS in NS was attributed to the increase in PDE5 activity, the enzyme responsible for the catabolism of cGMP, the intracellular NP's secondary messenger. This was accompanied in NS by marked reduction of cGMP urinary levels going along with resistance to the natriuretic response to NP's (8). It is well recognized that the natriuresis induced by NP's requires an intact RDS. An explanation for the RDS-NPS interaction was the finding that ANP can recruit silent D1R from the intracellular compartment towards the plasma membrane, where they become functionally active (9). Another potential pathway implicated in RDS-NPS interaction may involve DARPP-32, a phosphoprotein that acts as a third messenger in the DA signalling pathway (10); actually, inactivation of DARPP-32 was associated with lack in the ability of NP's to induce natriuresis (10). C. Evaluation of the effects of vitamin D3 (calcitriol) supplementation on NPS activity in PAN-NS. The influence of calcitriol on NP receptor A (NPR-A) and C (NPR-C) expression will be evaluated in the renal cortex and medulla, 7, 14 and 21 days after PAN administration. Calcitriol synthesis and plasma levels are reduced in NS (11,12). Gathered evidence shows that calcitriol can activate NPR-A gene transcription and increase cGMP production, namely in the inner medullary collecting ducts (6). D. Evaluation of the effects of calcitriol supplementation on cardiac remodelling and dysfunction in PAN-NS will be carried out at 7, 14 and 21 days after PAN administration by assessment of: a. Local expression of TNF-alfa, IL-1beta, TGF-beta1 and ET-1a b. Local expression of SERCA-2a and PLB c. Cardiac histomorphometry. NS is associated with increased cardiovascular risk that cannot be explained exclusively by traditional cardiovascular risk factors (7). Our group recently reported that the proinflammatory state induced by PAN-NS involves the heart and is accompanied by cardiac remodelling and dysfunction (4). Vitamin D3 synthesis and plasma levels are reduced in NS (11,12). Calcitriol was associated with potential cardioprotective effects (13,27). |