Acute pancreatitis is a disease associated with inflammation and tissue damage. One protein that protects against acute injury, including ischemic injury to both the kidney and heart, is renalase, which is secreted into the blood by the kidney and other tissues. However, whether renalase reduces acute injury associated with pancreatitis is unknown. Here, we used both and murine models of acute pancreatitis to study renalase's effects on this condition. In isolated pancreatic lobules, pretreatment with recombinant human renalase (rRNLS) blocked zymogen activation caused by cerulein, carbachol, and a bile acid. Renalase also blocked cerulein-induced cell injury and histological changes. In the cerulein model of pancreatitis, genetic deletion of renalase resulted in more severe disease, andadministering rRNLS to cerulein-exposed WT mice after pancreatitis onset was protective. Because pathological increases in acinar cell cytosolic calcium levels are central to the initiation of acute pancreatitis, we also investigated whether rRNLS could function through its binding protein, plasma membrane calcium ATPase 4b (PMCA4b), which excretes calcium from cells. We found that PMCA4b is expressed in both murine and human acinar cells and that a PMCA4b-selective inhibitor worsens pancreatitis-induced injury and blocks the protective effects of rRNLS. These findings suggest that renalase is a protective plasma protein that reduces acinar cell injury through a plasma membrane calcium ATPase. Because exogenous rRNLS reduces the severity of acute pancreatitis, it has potential as a therapeutic agent.

Alcohol abuse is a leading cause of pancreatitis, accounting for 30% of acute cases and 70 -90% of chronic cases, yet the mechanisms leading to alcohol-associated pancreatic injury are unclear. An early and critical feature of pancreatitis is the aberrant signaling of Ca 2؉ within the pancreatic acinar cell. An important conductor of this Ca 2؉ is the basolaterally localized, intracellular Ca 2؉ channel ryanodine receptor (RYR). In this study, we examined the effect of ethanol on mediating both pathologic intra-acinar protease activation, a precursor to pancreatitis, as well as RYR Ca 2؉ signals. We hypothesized that ethanol sensitizes the acinar cell to protease activation by modulating RYR Ca 2؉ . Acinar cells were freshly isolated from rat, pretreated with ethanol, and stimulated with the muscarinic agonist carbachol (1 M). Ethanol caused a doubling in the carbachol-induced activation of the proteases trypsin and chymotrypsin (p < 0.02). The RYR inhibitor dantrolene abrogated the enhancement of trypsin and chymotrypsin activity by ethanol (p < 0.005 for both proteases). Further, ethanol accelerated the speed of the apical to basolateral Ca 2؉ wave from 9 to 18 m/s (p < 0.0005; n ‫؍‬ 18 -22 cells/group); an increase in Ca 2؉ wave speed was also observed with a change from physiologic concentrations of carbachol (1 M) to a supraphysiologic concentration (1 mM) that leads to protease activation. Dantrolene abrogated the ethanol-induced acceleration of wave speed (p < 0.05; n ‫؍‬ 10 -16 cells/group). Our results suggest that the enhancement of pathologic protease activation by ethanol is dependent on the RYR and that a novel mechanism for this enhancement may involve RYR-mediated acceleration of Ca 2؉ waves.Pancreatitis is a life-threatening inflammatory disorder of the pancreas that leads to more than 30,000 deaths per year (1). Alcohol-associated pancreatitis accounts for 30% of acute cases and 70 -90% of chronic cases. Further, alcoholic pancreatitis carries the highest mortality rate among all etiologies (2). However, the mechanisms by which ethanol mediates pathology are largely unknown.Alcohol can exert diverse effects on the pancreas. Ethanol exposure has been linked to abnormal blood flow, leading to ischemic changes, and increased sphincter of Oddi dysfunction, resulting in pancreatic duct hypertension (2).In addition, ethanol appears to directly predispose the acinar cell to pathological changes including oxidant stress (3), membrane fragility (4), mitochondrial uncoupling (5, 6), and basolateral exocytosis (7). Several lines of evidence also link ethanol to aberrant Ca 2ϩ 3 signaling (6). High amplitude, aberrant, intracellular Ca 2ϩ waves that propagate from the apical to basolateral region of the acinar cell predispose to early features of pancreatitis, particularly intra-acinar protease activation (8, 9). We know that intracellular Ca 2ϩ release is responsible for the onset of this aberrant Ca 2ϩ signal (10). In addition, we have previously shown that the ryanodine receptor (RYR), 4 a major intracel...

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tracellular pH is observed in a number of clinical conditions and can sensitize to the development and worsen the severity of acute pancreatitis. Because intercellular communication through gap junctions is pH-sensitive and modulates pancreatitis responses, we evaluated the effects of low pH on gap junctions in the rat pancreatic acinar cell. Decreasing extracellular pH from 7.4 to 7.0 significantly inhibited gap junctional intracellular communication. Acidic pH also significantly reduced levels of connexin32, the predominant gap junction protein in acinar cells, and altered its localization. Increased degradation through the proteasomal, lysosomal, and autophagic pathways mediated the decrease in connexin32 under low-pH conditions. These findings provide the first evidence that low extracellular pH can regulate gap junctional intercellular communication by enhancing connexin degradation. cell pH; gap junctions; protein degradation; cell-cell interaction; pancreas; acinar cell GAP JUNCTIONS ARE INTERCELLULAR membrane channels composed of connexins that allow the movement of Ͻ1,000-Da molecules, including ions, secondary messengers, and small metabolites between cells. Gap junctions in pancreatic acinar cells are composed mainly of connexin32 (Cx32) (29). In Cx32-deficient mice, mild reversible cerulein-induced pancreatitis is converted to severe disease (8). Correspondingly, irsogladine, which strengthens gap junctional coupling, attenuates the severity of cerulein-induced pancreatitis in rats (15). These studies suggest that cell-to-cell communication through gap junctions plays an important role in modulating pancreatitis responses.Gap junctional intercellular communication (GJIC) is affected by two parameters: the number of hemichannels at the membrane and the gating of these hemichannels. Gating refers to the mechanism by which the intercellular passage of molecules is restricted and is dependent on the unitary conductance and open probability of each channel (32). Although connexin gating provides a rapid mechanism to modulate GJIC, regulation of connexin degradation has been proposed as another mechanism for controlling gap junction assembly and function (33). Cx32 degradation is complex, with established roles for proteasomal and lysosomal pathways (20,23,45). The autophagic pathway has been implicated in the degradation of some connexins (2, 6, 26) but has not been studied for Cx32.Acute and chronic reductions of extracellular pH are observed in a range of disease conditions and increase the risk and severity of acute pancreatitis. Using a cerulein model of pancreatitis, we have shown that reducing extracellular pH sensitizes to zymogen activation and cellular injury in vitro and pancreatitis in vivo (3). When exposed to acidic conditions, cells treated with a physiological, low dose of cerulein display pancreatitis responses similar to responses to supramaximal doses of cerulein (3, 39). However, the mechanism responsible for the injurious effects of lowering extracellular pH remains unclear. Low pH lea...