Luminal NaCl delivery regulates basolateral PGE2 release from macula densa cells

Area of Science:

• Renal Physiology
• Molecular Biology
• Cell Signaling

Background:

• Macula densa (MD) cells are known to express COX-2, and COX-2-derived prostaglandins (PGs) are implicated in renin release from the juxtaglomerular apparatus, particularly during volume depletion.
• However, the precise synthetic pathways and specific prostanoid released by intact MD cells remain unclear.

Purpose of the Study:

• To engineer a novel biosensor to directly detect prostaglandin E2 (PGE2) release from intact macula densa (MD) cells in response to reduced luminal NaCl concentration ([NaCl]L).
• To investigate the role of PGE2 in MD cell signaling and its potential contribution to renin release and renal vascular resistance control.

Main Methods:

• Development of a biosensor using HEK293 cells transfected with the Ca2+-coupled E-prostanoid receptor EP1 (HEK/EP1) and loaded with fura-2.
• Measurement of intracellular calcium ([Ca2+]i) in HEK/EP1 cells positioned at the basolateral surface of isolated perfused MD cells subjected to varying [NaCl]L.
• Assessment of COX-2 and microsome-associated PGE synthase (mPGES) expression in MD cells from rabbits on low-salt diets.

Main Results:

• Reduced [NaCl]L significantly elevated intracellular [Ca2+]i in HEK/EP1 cells, indicating PGE2 release from MD cells.
• This response was more pronounced in MD cells from rabbits on a low-salt diet and was inhibited by COX-2 and EP1 antagonists, as well as furosemide.
• Low-salt diet increased the expression of COX-2 and mPGES in the MD.

Conclusions:

• Intact macula densa cells synthesize and release PGE2 in response to decreased luminal salt concentration.
• This PGE2 release mechanism is directly evidenced for the first time and is likely important for controlling renin release and renal vascular resistance during salt deprivation.