Transmembrane guanylyl cyclases (GCs), with activity regulated by peptide ligands and/or calcium-binding proteins, are essential for various physiological and sensory processes. The mode of activation of the GC subtype GC-G, which is expressed in neurons of the Grueneberg ganglion that respond to cool temperatures, has been elusive. In searching for appropriate stimuli to activate GC-G, we found that its enzymatic activity is directly stimulated by cool temperatures. In this context, it was observed that dimerization/ oligomerization of GC-G, a process generally considered as critical for enzymatic activity of GCs, is strongly enhanced by coolness. Moreover, heterologous expression of GC-G in cultured cells rendered these cells responsive to coolness; thus, the protein might be a sensor for cool temperatures. This concept is supported by the observation of substantially reduced coolness-induced response of Grueneberg ganglion neurons and coolness-evoked ultrasonic vocalization in GC-G-deficient mouse pups. GC-G may be a novel thermosensory protein with functional implications for the Grueneberg ganglion, a sensory organ responding to cool temperatures.

The membrane forms of guanylyl cyclase (GC) serve as cell-surface receptors that synthesize the second messenger cGMP, which mediates diverse cellular processes. Rat kidney contains mRNA for the GC-G isoform, but the role of this receptor in health and disease has not been characterized. It was found that mouse kidney also contains GC-G mRNA, and immunohistochemistry identified GC-G protein in the epithelial cells of the proximal tubule and collecting ducts. Six hours after ischemia-reperfusion (I/R) injury, GC-G mRNA and protein expression increased three-fold and remained upregulated at 24 h. For determination of whether GC-G mediates I/R injury, a mutant mouse with a targeted disruption of the GC-G gene (Gucy2g) was created. At baseline, no histologic abnormalities were observed in GC-G Ϫ/Ϫ mice. After I/R injury, elevations in serum creatinine and urea were attenuated in GC-G Ϫ/Ϫ mice compared with wild-type controls, and this correlated with less tubular disruption, less tubular cell apoptosis, and less caspase-3 activation. Measures of inflammation (number of infiltrating neutrophils, myeloperoxidase activity, and induction of IL-6 and P-selectin) and activation of NF-B were lower in GC-G Ϫ/Ϫ mice compared with wild-type mice. Direct transfer of a GC-G expression plasmid to the kidneys of GC-G Ϫ/Ϫ mice resulted in a dramatically higher mortality after renal I/R injury, further supporting a role for GC-G in mediating injury. In summary, GC-G may act as an early signaling molecule that promotes apoptotic and inflammatory responses in I/R-induced acute renal injury.

The objective of this study was to evaluate the cardiac toxicity induced by carboplatin, a second generation platinum-containing anti-cancer drug, and to test whether pravastatin can reduce this cardio-toxicity. In the present study, infusion of carboplatin (100 mg/kg) to mice resulted in decreased survival rates and abnormal cardiac histology, concomitant with increased cardiac apoptosis. In addition, treatment of cultured rat cardiomyocytes with carboplatin (100 muM for 48 h) caused marked apoptosis and increased caspase-3, -9, and cytochrome C, but decreased BCL-XL protein expression, and this was inhibited by reactive oxygen species (ROS) scavenger n-acetylcysteine. Furthermore, pretreatment of cardiomyocytes with pravastatin (20 microM) before carboplatin exposure significantly attenuated apoptosis and decreased caspase-3, -9, cytochrome C activity. Lastly, mice pre-treated with pravastatin before carboplatin treatment showed improved survival rate and cardiac function, with reduced cardiomyocyte apoptosis via activating Akt and restoring normal mitochondrial HAX-1 in heart tissue. In summary, our results show that carboplatin can induce cardiotoxicity in vivo and in cultured cells via a mitochondrial pathway related to ROS production, whereas pravastatin administration can reduce such oxidative stress thus prevented cardiac apoptosis. Therefore, pravastatin can be used as a cytoprotective agent prior to carboplatin chemotherapy.

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