Terzic, André

Biomimetic biomaterials require good biocompatibility and bioactivity to serve as appropriate scaffolds for tissue engineering applications.

There is no therapy that promotes maturation and functionality of a dialysis arteriovenous fistula (AVF). The search for such therapies largely relies on evaluation of vascular responses and putative therapies in experimental AVFs. We studied an AVF in mice with chronic kidney disease (CKD). We demonstrate numerous stressors in the vein of the AVF-CKD group, including pathological shear, mitogenic, inflammatory, and hypoxia-reoxygenation stress. Because stress promotes premature senescence, we examined whether senescence is induced in the vein of the AVF-CKD model. We demonstrate a senescence phenotype in the AVF-CKD model, as indicated by increased expression of p16Ink4a, p21Cip1, and p53 and expected changes for certain senescence-associated microRNAs. RNA-sequencing analysis demonstrated differential expression of ~10,000 genes, including upregulation of proinflammatory and proliferative genes, in the vein of the AVF-CKD group. The vein in the AVF-CKD group exhibited telomere erosion and increased senescence-associated β-galactosidase activity and staining. Senescence was induced in the artery of the AVF-CKD group and in the vein of the AVF without CKD. Finally, given the rapidly rising clinical interest in senolytics, we provide proof of concept of senolytics as a therapeutic approach by demonstrating that senolytics decrease p16Ink4a expression in the AVF-CKD model. This study introduces a novel concept underlying the basis for maturational and functional failure in human dialysis AVFs and identifies a new target for senolytic therapy.

ABSTRACT Metabolic injury is a complex process affecting various tissues, with intracellular Ca 2+ loading recognized as a common precipitating event leading to cell death. We have recently observed that cells overexpressing recombinant ATP‐sensitive K + (K ATP ) channel subunits may acquire resistance against metabolic stress. To examine whether, under metabolic challenge, intracellular Ca 2+ homeostasis can be maintained by an activator of channel proteins, we delivered Kir6.2 and SUR2A genes, which encode K ATP channel subunits, into a somatic cell line lacking native K ATP channels. Hypoxia‐reoxygenation was simulated by application and removal of the mitochondrial poison 2,4 dinitrophenol. Under such metabolic stress, Ca 2+ loading was induced by Ca 2+ influx during hypoxia and release of Ca 2+ from intracellular stores during reoxygenation. Delivery of Kir6.2/SUR2A genes, in conjunction with the K ATP channel activator pinacidil, prevented intracellular Ca 2+ loading irrespective of whether the channel opener was applied throughout the duration of hypoxia‐reoxygenation or transiently during the hypoxic or reoxygenation stage. In all stages of injury, the effect of pinacidil was inhibited by the selective antagonist of K ATP channel, 5‐hydroxydecanoate. The present study provides evidence that combined use of gene delivery and pharmacological targeting of recombinant proteins can handle intracellular Ca 2+ homeostasis under hypoxia‐reoxygenation irrespective of the stage of the metabolic insult.—Jovanović, N., Jovanović, S., Jovanović, A., Terzic, A. Gene delivery of Kir6.2/SUR2A in conjunction with pinacidil handles intracellular Ca 2+ homeostasis under metabolic stress. FASEB J. 13, 923–929 (1999)

ABSTRACT Bacteria that produce heat‐stable enterotoxins (STs), a leading cause of secretory diarrhea, are a major cause of morbidity and mortality worldwide. ST stimulates guanylyl cyclase C (GCC) and accumulation of intracellular cyclic GMP ([cGMP] i ), which opens the cystic fibrosis transmembrane conductance regulator (CFTR)‐related chloride channel, triggering intestinal secretion. Although the signaling cascade mediating ST‐induced diarrhea is well characterized, antisecretory therapy targeting this pathway has not been developed. 2‐ChloroATP (2ClATP) and its cell‐permeant precursor, 2‐chloroadenosine (2ClAdo), disrupt ST‐dependent signaling in intestinal cells. However, whether the ability to disrupt guanylyl cyclase signaling translates into effective antisecretory therapy remains untested. In this study, the efficacy of 2ClAdo to prevent ST‐induced water secretion by human intestinal cells was examined. In Caco‐2 human intestinal cells, ST increased [cGMP] i , induced a chloride current, and stimulated net basolateral‐to‐apical water secretion. This effect on chloride current and water secretion was mimicked by the cell‐permeant analog of cGMP, 8‐bromo‐cGMP. Treatment of Caco‐2 cells with 2ClAdo prevented ST‐induced increases in [cGMP] i , chloride current and water secretion. Inhibition of the downstream consequences of ST‐GCC interaction reflects proximal disruption of cGMP production because 8‐bromo‐cGMP stimulated chloride current and water secretion in 2ClAdo‐treated cells. Thus, this study demonstrates that disruption of guanylyl cyclase signaling is an effective strategy for antisecretory therapy and provides the basis for developing mechanism‐based treatments for enterotoxigenic diarrhea.—Zhang, W., Mannan, I., Schulz, S., Parkinson, S. J., Alekseev, A. E., Gomez, L. A., Terzic, A., Waldman, S. A. Interruption of transmembrane signaling as a novel antisecretory strategy to treat enterotoxigenic diarrhea. FASEB J. 13, 913–922 (1999)

ATP‐sensitive K + (K ATP ) channels are nucleotide‐gated channels that couple the metabolic status of a cell with membrane excitability and regulate a number of cellular functions, including hormone secretion and cardioprotection. Although intracellular ATP is the endogenous inhibitor of K ATP channels and ADP serves as the channel activator, it is still a matter of debate whether changes in the intracellular concentrations of ATP, ADP, and/or in the ATP/ADP ratio could account for the transition from the ATP‐liganded to the ADP‐liganded channel state. Here, we overview evidence for the role of cellular phosphotransfer cascades in the regulation of K ATP channels. The microenvironment of the K ATP channel harbors several phosphotransfer enzymes, including adenylate, creatine, and pyruvate kinases, as well as other glycolytic enzymes that are able to transfer phosphoryls between ATP and ADP in the absence of major changes in cytosolic levels of adenine nucleotides. These phosphotransfer reactions are governed by the metabolic status of a cell, and their phosphotransfer rate closely correlates with K ATP channel activity. Adenylate kinase catalysis accelerates the transition from ATP to ADP, leading to K ATP channel opening, while phosphotransfers driven by creatine and pyruvate kinases promote ADP to ATP transition and channel closure. Thus, through delivery and removal of adenine nucleotides at the channel site, phosphotransfer reactions could regulate ATP/ADP balance in the immediate vicinity of the channel and thereby the probability of K ATP channel opening. In this way, phosphotransfer reactions could provide a transduction mechanism coupling cellular metabolic signals with K ATP channel‐associated functions.

ABSTRACT Mutations in genes encoding ion channels have increasingly been identified to cause disease conditions collectively termed channelopathies. Recognizing the molecular basis of an ion channel disease has provided new opportunities for screening, early diagnosis, and therapy of such conditions. This synopsis provides an overview of progress in the identification of molecular defects in inwardly rectifying potassium (Kir) channels. Structurally and functionally distinct from other channel families, Kir channels are ubiquitously expressed and serve functions as diverse as regulation of resting membrane potential, maintenance of K + homeostasis, control of heart rate, and hormone secretion. In humans, persistent hyperinsulinemic hypoglycemia of infancy, a disorder affecting the function of pancreatic β cells, and Bartter's syndrome, characterized by hypokalemic alkalosis, hypercalciuria, increased serum aldosterone, and plasma renin activity, are the two major diseases linked so far to mutations in a Kir channel or associated protein. In addition, the weaver phenotype, a neurological disorder in mice, has also been associated with mutations in a Kir channel subtype. Further genetic linkage analysis and full understanding of the consequence that a defect in a Kir channel would have on disease pathogenesis are among the priorities in this emerging field of molecular medicine.—Abraham, M. R., Jahangir, A., Alekseev, A. E., Terzic, A. Channelopathies of inwardly rectifying potassium channels. FASEB J . 13, 1901–1910 (1999)

ATP-sensitive K+ (KATP) channels are present at high density in membranes of cardiac cells where they regulate cardiac function during cellular metabolic impairment. KATP channels have been implicated in the shortening of the action potential duration and the cellular loss of K+ that occurs during metabolic inhibition. KATP channels have been associated with the cardioprotective mechanism of ischemia-related preconditioning. Intracellular ATP (ATPi) is the main regulator of KATP channels. ATPi has two functions: 1) to close the channel (ligand function) and 2) in the presence of Mg2+, to maintain the activity of KATP channels (presumably through an enzymatic reaction). KATP channel activity is modulated by intracellular nucleoside diphosphates that antagonize the ATPi-induced inhibition of channel opening or induce KATP channels to open. How nucleotides will affect KATP channels depends on the state of the channel. K+ channel-opening drugs are pharmacological agents that enhance KATP channel activity through different mechanisms and have great potential in the management of cardiovascular conditions. KATP channel activity is also modulated by neurohormones. Adenosine, through the activation of a GTP-binding protein, antagonizes the ATPi-induced channel closure. Understanding the molecular mechanisms that underlie KATP channel regulation should prove essential to further define the function of KATP channels and to elucidate the pharmacological regulation of this channel protein. Since the molecular structure of the KATP channel has now become available, it is anticipated that major progress in the KATP channel field will be achieved.