Biology subjects

Kuo, I. Y.

Publications and source records attributed to Kuo, I. Y..

5 recordsLinked to original sources

bioRxiv2025

Polycystin-2 is cardioprotective against myocardial infarction by regulating the calcium-mediated ER stress response.

BackgroundPatients with autosomal polycystic kidney disease (ADPKD) have an increased risk and worsened outcomes for acute myocardial infarction (AMI), but the mechanism behind this is unknown. Polycystin 2 (PC2), the protein encoded by one of the two main genes mutated in ADPKD, is a calcium-permeant channel ubiquitously expressed; however, its role in cardiomyocytes remains poorly understood. One hallmark of AMI is ER stress, which PC2 is known to regulate adaptively; however, whether PC2 regulates ER stress in the ischemic heart is unknown. ObjectiveThis study investigates the mechanism by which PC2 regulates ER stress in myocardial ischemia. Methods and ResultsPC2 protein was increased in human ischemic heart failure samples and murine myocardial infarct samples, and it was enriched at ER-mitochondrial contact sites. Induction of myocardial infarction (MI) in cardiomyocyte-specific PC2-KO mice led to cardiac dysfunction and reduced PERK expression compared to control MI mice. ER stress induced by tunicamycin in vitro blunted PERK phosphorylation and subsequent CHOP upregulation in PC2 KO cells. Tunicamycin-induced ER stress resulted in a PC2-dependent ER calcium leak and mitochondrial calcium transients, along with increased mitochondrial function, all of which were decreased in PC2 KO cells. Moreover, PC2 KO cells after ER stress exhibited decreased mitochondrial membrane potential and increased apoptosis. Isolated WT cardiomyocytes exhibited increased diastolic calcium after acute ER stress induction and increased mitochondrial uptake, neither of which was seen in PC2 KO cells. Re-expression of full-length PC2 in vitro restored both the calcium leak and PERK phosphorylation in PC2 KO cells under ER stress, but not a pathological mutant PC2 D511V, which impairs ion channel activity. ConclusionsPC2 is upregulated during ER stress, where it localizes at ER-mitochondrial contact sites and acts as an ER calcium leak channel, thereby restoring cellular homeostasis during the adaptive phase of ER stress. PC2 provides cardioprotection during ischemic events by preventing maladaptive ER stress, which contributes to cardiac dysfunction. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=194 SRC="FIGDIR/small/668747v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1e416d5org.highwire.dtl.DTLVardef@1971fd9org.highwire.dtl.DTLVardef@abeebcorg.highwire.dtl.DTLVardef@1c68f8d_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2024

Cardiac Localized Polycystin-2 plays a Functional Role in Natriuretic Peptide Production and its Absence Contributes to Hypertension

Cardiovascular complications are the most common cause of mortality in patients with autosomal dominant polycystic kidney disease (ADPKD). Hypertension is seen in 70% of patients by the age of 30 prior to decline in kidney function. The natriuretic peptides (NPs), atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), are released by cardiomyocytes in response to membrane stretch, increasing urinary excretion of sodium and water. Mice heterozygous for Pkd2 have attenuated NP responses and we hypothesized that cardiomyocyte-localized polycystin proteins contribute to production of NPs. Cardiomyocyte-specific knock-out models of polycystin-2 (PC2), one of the causative genes of ADPKD, demonstrate diurnal hypertension. These mice have decreased ANP and BNP expression in the left ventricle. Analysis of the pathways involved in production, maturation, and activity of NPs identified decreased transcription of CgB, PCSK6, and NFAT genes in cPC2-KOs. Engineered heart tissue with human iPSCs driven into cardiomyocytes with CRISPR/Cas9 KO of PKD2 failed to produce ANP. These results suggest that PC2 in cardiomyocytes are involved in NP production and lack of cardiac PC2 predisposes to a hypertensive volume expanded phenotype, which may contribute to the development of hypertension in ADPKD.

physiology↗

bioRxiv2023

Utilization of the genetically encoded calcium indicator Salsa6F in cardiac applications

Calcium signaling is a critical process required for cellular mechanisms such as cardiac contractility. The inability of the cell to properly activate or regulate calcium signaling can lead to contractile dysfunction. In isolated cardiomyocytes, calcium signaling has been primarily studied using calcium fluorescent dyes, however these dyes have limited applicability to whole organs. Here, we crossed the Salsa6f mouse which expresses a genetically encoded ratiometric cytosolic calcium indicator with a cardiomyocyte specific inducible cre to temporally-induce expression and studied cytosolic calcium transients in isolated cardiomyocytes and modified Langendorff heart preparations. Isolated cardiomyocytes expressing Salsa6f or Fluo-4AM loaded were compared. We also crossed the Salsa6f mouse with a floxed Polycystin 2 (PC2) mouse to test the feasibility of using the Salsa6f mouse to measure calcium transients in PC2 heterozygous or homozygous knock out mice. Although there are caveats in the applicability of the Salsa6f mouse, there are clear advantages to using the Salsa6f mouse to measure whole heart calcium signals.

physiology↗

bioRxiv2023

TRiPPing the sensors: The osmosensing pathway of Polycystin 2

Mutations to polycystin-2 (PC2), a non-selective cation permeant transient receptor potential channel, results in polycystic kidney disease (PKD). Despite the disease relevance of PC2, the physiological agonist that activates PC2 has remained elusive. As one of the earliest symptoms in PKD is a urine concentrating deficiency, we hypothesized that shifts in osmolarity experienced by the collecting duct cells would activate PC2 and loss of PC2 would prevent osmosensing. We found that mice with inducible PC2 knocked out (KO) in renal tubules had dilute urine. Hyperosmotic stimuli induced a rise in endoplasmic reticulum (ER)-mediated cytosolic calcium which was absent in PC2 KO mice and PC2 KO cells. A pathologic point mutation that prevents ion flux through PC2 inhibited the calcium rise, pointing to the centrality of PC2 in the osmotic response. To understand how an extracellular stimulus activated ER-localized PC2, we examined microtubule-ER dynamics, and found that the osmotically induced calcium increase was preceded by microtubule destabilization. This was due to a novel interaction between PC2 and the microtubule binding protein MAP4 that tethers the microtubules to the ER. Finally, disruption of the MAP4-PC2 interaction prevented incorporation of the water channel aquaporin 2 following a hyperosmotic challenge, in part explaining the dilute urine. Our results demonstrate that MAP4-dependent microtubule stabilization of ER-resident PC2 is required for PC2 to participate in the osmosensing pathway. Moreover, osmolarity represents a bona fide physiological stimulus for ER-localized PC2 and loss of PC2 in renal epithelial cells impairs osmosensing ability and urine concentrating capacity. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=92 SRC="FIGDIR/small/540007v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@1ddf689org.highwire.dtl.DTLVardef@164a89corg.highwire.dtl.DTLVardef@179d1dforg.highwire.dtl.DTLVardef@c1be99_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2020

Calcium signaling through a Transient Receptor Channel is important for Toxoplasma gondii growth

Transient Receptor Potential (TRP) channels participate in ion calcium (Ca2+) influx and intracellular Ca2+ release. TRP channels have not been studied in Toxoplasma gondii or any other Apicomplexan parasite. We characterized a protein predicted to possess a TRP domain (TgTRPPL-2) and determined its role in Ca2+ signaling in T. gondii, the causative agent of toxoplasmosis. TgTRPPL-2 localized to the plasma membrane and the endoplasmic reticulum of T. gondii. The{Delta} TgTRPPL-2 mutant was defective in growth and Ca2+ influx. Heterologous expression of TgTRPPL-2 in HEK-3KO cells allowed its functional characterization. Patching of ER-nuclear membranes demonstrated that TgTRPPL-2 is a non-selective cation channel that conducts Ca2+. Pharmacological blockers of TgTRPPL-2 inhibited Ca2+ influx and parasite growth. This is the first report of an Apicomplexan channel that conducts Ca2+ and initiates the Ca2+ signaling cascade that culminates in the stimulation of motility, invasion and egress. TgTRPPL-2 is a potential target for combating toxoplasmosis.

microbiology↗