# Opposite Effects of Diacylglycerol and Phosphatidic Acid in the Modulation of the Plasma Membrane Ca2+-ATPase from Kidney Proximal Tubules: A Regulatory Role for Diacylglycerol Kinase in Calcium Homeostasis?

## TL;DR

This study explores how two bioactive lipids, diacylglycerol and phosphatidic acid, opposingly regulate calcium transport in kidney cells, suggesting a role for diacylglycerol kinase in calcium balance.

## Contribution

The paper reveals opposing regulatory effects of DG and PA on PMCA activity and identifies a novel DG-DGK-PA axis in calcium signaling under metabolic stress.

## Key findings

- Diacylglycerol inhibits PMCA activity via PKC-dependent phosphorylation.
- Phosphatidic acid stimulates PMCA activity, showing opposing regulation.
- Transcriptomic data suggest DG accumulation and PMCA upregulation under hypoxia.

## Abstract

Background/Objectives: Kidney proximal tubules reabsorb up to 70% of water and solutes from the glomerular ultrafiltrate, a Ca2+-modulated process essential for homeostasis. The plasma membrane Ca2+-ATPase (PMCA) in basolateral membranes (BLMs) plays a pivotal role in maintaining intracellular calcium homeostasis and regulating calcium reabsorption. Methods: Here, we investigated the regulatory influence of two key bioactive lipids, diacylglycerol (DG) and phosphatidic acid (PA), on PMCA activity from pig kidney, accompanied by lipidomic assays and transcriptomic data analyses. Results: Biochemical assays revealed dose- and time-dependent inhibition of PMCA by DG, fully reversed by Calphostin C, implicating PKC activation. Conversely, PA significantly stimulated PMCA activity, demonstrating an opposite regulatory effect. Our targeted lipidomics identified multiple DG species in HK-2 cells, suggesting substrate diversity. Analysis of transcriptomic data for hypoxic versus normoxic HK-2 cells revealed dramatic coordinated regulation of DG/PA metabolism genes, with upregulation of DG-producing enzymes (PLCB1, PLDs) and downregulation of DG-consuming kinases (DGKs), predicting enhanced DG accumulation under metabolic stress. ATP2B4 (PMCA4) upregulation indicated compensatory transcriptional responses. Conclusions: Our findings suggest that DG inhibits BLM-associated PMCA via classic and/or atypical PKC-dependent phosphorylation while PA exerts opposing stimulatory effects. Both transcriptional remodeling and post-translational modifications regulate this axis. These findings highlight the DG–Diacylglycerol Kinase–PA axis as a dynamic modulator of Ca2+ signaling in the kidney that responds to metabolic stress.