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[PMC free article] [PubMed] [Google Scholar] 9


Dec 7, 2021

[PMC free article] [PubMed] [Google Scholar] 9. mediators of cellular homeostasis.1,2 Ca2+ permeates the membrane of virtually every cell to regulate diverse vital processes such as muscle contraction, cytoskeletal structure, vesicle secretion, gene transcription, and programmed cell death, to name a few.1,2 Thousands of Ca2+ channels on the plasma membrane precisely control the timing and entry of Ca2+ ions and cellular homeostatic mechanisms modulate the tight control and compartmentalization of these intracellular Ca2+ transients (Figure 1).2 Open in a separate window Figure 1. Schematic representation of Ca2+ homeostasis in podocytes Ca2+ is a potent signaling molecule because of its ability to mediate a dynamic, dramatic, transient, and tightly regulated range of intracellular responses1,2,9 (PM: plasma membrane). Some proteins shown here have not yet been identified or studied in podocytes (calbindins, the mitochondrial uniporter or MiCa etc.), but they are likely to be present based on our understanding of calcium homeostasis in other cell types. The influx of Ca2+ is likely to be mediated by TRPC5 and TRPC6 channels, which were recorded at the single channel level in podocytes,37 but other influx pathways cannot be excluded. TRPC5 and TRPC6 are activated by upstream receptors such as G-protein coupled receptors (GPCR), including the AT1R, and receptor tyrosine kinases (RTK), Atuveciclib (BAY-1143572) similar to other cell types.62 Ca2+ is tightly regulated upon entry into the cytoplasm. Calcium homeostasis relies on the Na+-Ca2+ exchanger (NCX), which has been described in podocytes,110 the ATP-dependent plasma membrane Ca2+ pump (PMCA), plasma Ca2+ buffers (calbindins, parvalbumin, etc.) and internal Ca2+ stores (endoplasmic reticulum (ER), mitochondria) to maintain low cytoplasmic Ca2+ levels.8 When a Ca2+-permeable channel opens, whether in the plasma membrane or on a Ca2+-loaded organelle (the IP3R in the Atuveciclib (BAY-1143572) ER), Ca2+ ions flow transiently into the cytoplasm, until the homeostatic mechanisms take over once again to buffer or extrude the excess Ca2+ ions. Here, we review the emerging role of Ca2+ signaling in the regulation of podocyte function in health and disease (Figure 2). In particular, we explore recently uncovered insights into the activation of transient receptor potential canonical (TRPC) channels by Ang II and the resulting effects on podocyte signaling under physiologic and pathologic conditions (Figure 3). Finally, we highlight the implications of balancing Ca2+-controlled signaling pathways in podocytes for the development of novel antiproteinuric therapies (Figure 4). Open in a separate window Figure 2. Atuveciclib (BAY-1143572) Evolution of calcium signaling in podocytes from 1978 to today. Open in a separate window Figure 3. Antagonistic activities of TRPC5 TRPC6 signaling in podocytes in health and disease: Is it a Atuveciclib (BAY-1143572) balancing act? This working model attempts to synthesize published data and underscore the areas in which future experiments are likely to enhance our understanding of TRPC Vegfb signaling in podocytes. (A) Under physiologic conditions, active TRPC6 channels are more abundant on the podocyte cell membrane, as demonstrated on the single channel level,37 which underscores their importance for maintaining podocyte integrity, through their selective activation of RhoA.37,46 (B) TRPC6 gain of function mutations20,36,111 result in overactive TRPC6 channels, the cell is overwhelmed by TRPC6-mediated Ca2+ influx, which ultimately leads to FSGS.83 The observed podocyte injury may result either broadly from Ca2+ cytotoxicity and cell death or specifically from excessive RhoA-mediated contraction, for example, increased stiffness leading to a broken actin cytoskeleton, and ultimately, cell death. (C) Given the experimental evidence that (a) constitutive Rac1 activity leads to proteinuria,76 (b) TRPC5 activates Rac1 in podocytes,37 and (c) Rac1 is required for TRPC5 insertion into the plasma membrane in podocytes,37 it is reasonable to hypothesize that, in states of excess AngII, TRPC5/Rac1Cmediated overactivity drives proteinuria. This notion generates interest in TRPC5 channels as mediators of acquired, Ang IICdriven proteinuria. Open in a separate window Figure 4. A model for multiple signaling pathways in podocyte injury: Atuveciclib (BAY-1143572) Is a multidrug, synergistic therapy the answer to proteinuria? A synthesis of work by many groups suggests that multiple signaling levels are involved in the Ang IICmediated regulation of.