Primary cilia dysfunction has been linked to numerous human diseases and genetic disorders, which present with a wide range of clinical features. Primary cilia have been found on the macula densa cells, but its role in the regulation of kidney function is unclear. The macula densa mediates tubuloglomerular feedback (TGF) by detecting the increases in NaCl concentration and promoting the release of adenosine or ATP that constricts the afferent arteriole. However, little is known about the role of cilia in the macla densa in the regulation of renal hemodynamics, salt and water excretion. Our preliminary data indicate that elevations in tubular flow in the isolated perfused juxtaglomerular apparatus (JGA) preparations increase macula densa intracellular calcium concentration, activates nitric oxide synthase 1 (NOS1) and attenuates TGF response. However, the role of the cilia on the macula densa as the flow sensor initiating this response remains to be determined. Normally increases in sodium delivery to the macula densa induce TGF response and constrict the afferent arteriole. However, following volume expansion in response to salt loading, sodium reabsorption in the proximal tubule is inhibited resulting in sustained elevations in flow to the macula densa. Under these conditions we propose that the primary cilia are stimulated, raise intracellular calcium and enhance the formation of nitric oxide that inhibits and resets TGF response. The resetting of TGF is an essential modulatory mechanism to allow for the rapid excretion of a salt load by preventing a fall in glomerular filtration rate (GFR). We further propose that deletion of the cilia or NOS1 of the macula densa prevents flow modulation of TGF responsiveness and impairs the excretion of a salt load by preventing the rise in GFR following volume expansion, hence promotes the development of salt-sensitive hypertension.
In this proposal we will study the role and mechanisms of tubuloglomerular feedback modulated by the primary cilia and nitric oxide in control of renal hemodynamics, salt and water balance and blood pressure.
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