Urocortin-1 Is Chondroprotective in Response to Acute Cartilage Injury via Modulation of Piezo1.

Post-traumatic OA (PTOA) is often triggered by injurious, high-impact loading events which result in rapid, excessive chondrocyte cell death and a phenotypic shift in residual cells toward a more catabolic state. As such, the identification of a disease-modifying OA drug (DMOAD) that can protect chondrocytes from death following impact injury, and thereby prevent cartilage degradation and progression to PTOA, would offer a novel intervention. We have previously shown that urocortin-1 (Ucn) is an essential endogenous pro-survival factor that protects chondrocytes from OA-associated pro-apoptotic stimuli. Here, using a drop tower PTOA-induction model, we demonstrate the extent of Ucn's chondroprotective role in cartilage explants exposed to excessive impact load. Using pathway-specific agonists and antagonists, we show that Ucn acts to block load-induced intracellular calcium accumulation through blockade of the non-selective cation channel Piezo1 rather than TRPV4. This protective effect is mediated primarily through the Ucn receptor CRF-R1 rather than CRF-R2. Crucially, we demonstrate that the chondroprotective effect of Ucn is maintained whether it is applied pre-impact or post-impact, highlighting the potential of Ucn as a novel DMOAD for the prevention of injurious impact overload-induced PTOA.

Cathepsin K inhibitors prevent matrix-derived growth factor degradation by human osteoclasts.

The coupling between bone formation and resorption creates a therapeutic impasse in osteoporosis: antiresorptive therapy halts bone loss, but also inhibits bone formation, and therefore does not cure the condition. Surprisingly, recent preliminary reports suggest that inhibition of resorption by cathepsin K (CathK) inhibitors augments bone formation. Uniquely amongst resorption-inhibitors, CathK-inhibitors suppress degradation of the organic matrix of bone while allowing demineralization. We hypothesized that these unique characteristics might explain a capacity of CathK inhibitors to enhance bone formation: the inhibitors might prevent degradation not only of collagen, but also other proteins, including growth factors embedded in matrix. We tested this hypothesis using osteocalcin and insulin-like growth factor I (IGF-I) as examples of matrix-embedded proteins, and found that CathK-inhibitors, unlike other resorption-inhibitors, dramatically increased the concentrations of these matrix-derived proteins in supernatants of osteoclasts on bone, most likely through protection against intracellular degradation. We found that protons are both necessary and sufficient for the release of IGF-I from bone matrix, and that recombinant CathK can degrade both marker proteins. In the presence of a CathK-inhibitor, the amount of IGF-I released from matrix substantially exceeded the amount secreted by osteoclasts. CathK-inhibition similarly augmented bone morphogenetic protein (BMP)-2 release. Lastly, MC3T3-E1 numbers were greater after co-culture with osteoclasts on bone with versus without CathK-inhibitor, showing that, in the presence of CathK-inhibitor, osteoclasts release biologically-significant quantities of biologically-active matrix-derived growth factors. These results support a model in which osteoclastic secretion of protons demineralizes bone, causing release of growth factors from bone matrix. Normally these are largely degraded, with collagen, in the resorptive hemivacuole and during transcytosis to the basal surface of the osteoclast, but in the presence of CathK inhibitor they are released intact, and so might augment bone formation.

Free radical scavenging inhibits STAT phosphorylation following in vivo ischemia/reperfusion injury.

The signal transducer and activator of transcription (STAT) family are latent transcription factors involved in a variety of signal transduction pathways, including cell death cascades. STAT1 has been shown to have a crucial role in regulating cardiac cell apoptosis in the myocardium exposed to ischemia/reperfusion (I/R) injury. The free radical scavenger, tempol, is known to have cardioprotective properties, although little is known about the molecular mechanism(s) by which it acts. In the present study, we assessed the levels of phosphorylated STAT1 and STAT3 and examined whether tempol was able to affect STAT activation after in vivo cardiac I/R injury. We observed a reperfusion time-dependent increase in the tyrosine phosphorylation of STAT1 and STAT3 at residues 701 and 705, respectively. Here we show for the first time that tempol dramatically reduced STAT1 and 3 phosphorylation. The reduction in STAT1 and 3 phosphorylation was accompanied by a concomitant decrease in cellular malondialdehyde (MDA) levels. To verify the role of STAT1 in modulating the cardioprotective effect of tempol, rats were injected with the STAT1 activator, IFN-gamma, and tempol during I/R injury. We found that the presence of IFN-gamma abrogated the protective effects of tempol, suggesting that the protective effects of tempol may partly operate by decreasing the phosphorylation of STAT1. This study demonstrates that careful dissection of the molecular mechanisms that underpin I/R injury may reveal cardioprotective targets for future therapy.

Urocortin suppresses endometrial cancer cell migration via CRFR2 and its system components are differentially modulated by estrogen.

Urocortin (UCN1) peptide shares structural and functional homology with corticotropin-releasing factor (CRF). UCN1 is significantly reduced in endometrial adenocarcinoma compared to healthy controls. However, there are no data which evaluate the effects of UCN1 in the endometrium, or how it is modulated. We used proliferation and transwell assays to determine the effect of UCN1 on the proliferation and migration of Ishikawa and HEC1A cells. We also determined the expression levels of UCN1 and its receptors produced by estrogen receptor agonists, and the effect of UCN1 on estrogen receptor expression, using quantitative polymerase chain reaction. UCN1 suppressed migration of endometrial cancer cells in vitro. This effect appears to be specific to CRF receptor 2 (CRFR2), as selective antagonism of CRFR2 but not CRFR1 completely eliminated suppression of migration. Activation of ERA reduced UCN1 expression, but only had a small effect on the expression of CRFR1. However, expression of CRFR2 was more notably reduced at both the mRNA and protein levels by activation of ERB. UCN1 in turn reduced both ERA and ERB expression, as assessed by real-time quantitative PCR. We demonstrate that UCN1 significantly suppresses the migration of endometrial cancer cells but has no effect on their proliferation. Thus, loss of UCN1 in endometrial cancer may promote invasion and metastatic spread. There is a complex relationship between the UCN1 system and estrogen receptors, which may provide insights into endometrial carcinogenesis, a disease known to be driven by estrogen excess.

The cardioprotective agent urocortin induces expression of CT-1.

The corticotrophin-releasing hormone-related factor, urocortin (Ucn) and the interleukin (IL)-6 family cytokine cardiotrophin-1 (CT-1) are both cardioprotective agents able to protect the heart from ischemic damage. In both cases the protective effect involves activation of the p42/p44 MAPK and PI-3 kinase/Akt pathways, but the protective effect of Ucn requires de novo protein synthesis whereas that of CT-1 does not. In this study, we show that Ucn induces enhanced expression of CT-1 at both the mRNA and protein levels. This effect is mediated by activation of the CT-1 gene promoter and requires the transcription factor C/EBPbeta/NF-IL6. Hence, a specific cardioprotective factor can induce enhanced expression of another cardioprotective factor belonging to an unrelated protein family.

Hormone-stimulated modulation of endocytic trafficking in osteoclasts.

A precise control of vesicular trafficking is crucial not only for osteoclastic bone resorption, but also for the crosstalk between osteoclasts and osteoblasts, which regulates bone homeostasis. In addition to the release of growth factors and modulators, such as glutamate, flux through the intracellular trafficking routes could also provide the osteoclast with a monitoring function of its resorption activity. To establish the signaling pathways regulating trafficking events in resorbing osteoclasts, we used the bone conserving hormone calcitonin, which has the unique property of inducing osteoclast quiescence. Calcitonin acts through the calcitonin receptor and activates multiple signaling pathways. By monitoring trafficking of a fluorescent low molecular weight probe in mature, bone resorbing osteoclasts we show for the first time that calcitonin blocks endocytosis from the ruffled border by phospholipase C (PLC) activation. Furthermore, we identify a requirement for polyunsaturated fatty acids in endocytic trafficking in osteoclasts. Inhibition of PLC prior to calcitonin treatment restores endocytosis to 75% of untreated rates. This effect is independent of protein kinase C activation and can be mimicked by an increase in intracellular calcium. We thus define an essential role for intracellular calcium levels in the maintenance of endocytosis in osteoclasts.

Urocortin is a novel regulator of osteoclast differentiation and function through inhibition of a canonical transient receptor potential 1-like cation channel.

This study investigated the role of urocortin (UCN), a member of the corticotrophin-releasing factor (CRF) family of peptides, in osteoclast maturation and function. We found that 10(-7) M UCN significantly (P<0.05) suppressed osteoclast differentiation from bone marrow precursor cells in culture and reduced the expression of several osteoclastic markers. Furthermore, UCN potently suppressed osteoclast bone resorption, by significantly inhibiting both the plan area of bone resorbed by osteoclasts and actin ring formation within osteoclasts at 10(-9) M (P<0.05), with complete inhibition at 10(-7) M (P<0.001). UCN also inhibited osteoclast motility (10(-7) M) but had no effect on osteoclast survival. Osteoclasts expressed mRNA encoding both UCN and the CRF receptor 2ß subtype. Pre-osteoclasts however, expressed CRF receptor 2ß alone. Unstimulated osteoclasts contained constitutively active cation channel currents with a unitary conductance of 3-4 pS, which were inhibited by over 70% with UCN (10(-7) M). Compounds that regulate calcium signalling and energy status of the cell, both crucial for osteoclast activity were investigated. The non-selective cation channel blockers, lanthanum (La(3)(+)) and gadolinium (Gd(3)(+)), inhibited actin ring formation in osteoclasts, whereas modulators of voltage-dependent Ca(2)(+) channels and K(ATP) channels had no effect. These findings show for the first time that UCN is a novel anti-resorptive molecule that acts through a direct effect on osteoclasts and their precursor cells.

New targets of urocortin-mediated cardioprotection.

The urocortin (UCN) hormones UCN1 and UCN2 have been shown previously to confer significant protection against myocardial ischaemia/reperfusion (I/R) injury; however, the molecular mechanisms underlying their action are poorly understood. To further define the transcriptional effect of UCNs that underpins their cardioprotective activity, a microarray analysis was carried out using an in vivo rat coronary occlusion model of I/R injury. Infusion of UCN1 or UCN2 before the onset of reperfusion resulted in the differential regulation of 66 and 141 genes respectively, the majority of which have not been described previously. Functional analysis demonstrated that UCN-regulated genes are involved in a wide range of biological responses, including cell death (e.g. X-linked inhibitor of apoptosis protein), oxidative stress (e.g. nuclear factor erythroid derived 2-related factor 1/nuclear factor erythroid derived 2-like 1) and metabolism (e.g. Prkaa2/AMPK). In addition, both UCN1 and UCN2 were found to modulate the expression of a host of genes involved in G-protein-coupled receptor (GPCR) signalling including Rac2, Gnb1, Dab2ip (AIP1), Ralgds, Rnd3, Rap1a and PKA, thereby revealing previously unrecognised signalling intermediates downstream of CRH receptors. Moreover, several of these GPCR-related genes have been shown previously to be involved in mitogen-activated protein kinase (MAPK) activation, suggesting a link between CRH receptors and induction of MAPKs. In addition, we have shown that both UCN1 and UCN2 significantly reduce free radical damage following myocardial infarction, and comparison of the UCN gene signatures with that of the anti-oxidant tempol revealed a significant overlap. These data uncover novel gene expression changes induced by UCNs, which will serve as a platform to further understand their mechanism of action in normal physiology and cardioprotection.

The selective PPARgamma antagonist GW9662 reverses the protection of LPS in a model of renal ischemia-reperfusion.

BACKGROUND: We have recently reported that pretreatment of rats with endotoxin (lipopolysaccharide, LPS) and selective agonists of the nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma) protect the kidney against ischemia/reperfusion (I/R) injury. Here we investigate the hypothesis that the renoprotective effects of LPS may be due to an enhanced formation of endogenous ligands of PPARgamma, rather than an up-regulation of PPARgamma expression. METHODS: Rats were pretreated with LPS (1 mg/kg, IP, 24 hours prior to ischemia) in the absence (control) or presence of the selective PPARgamma antagonist GW9662 (1 mg/kg, IP, 24 and 12 hours prior to ischemia). Twenty-four hours after injection of LPS, rats were subjected to 60 minutes of bilateral renal ischemia, followed by 6 hours of reperfusion. Serum and urinary indicators of renal injury and dysfunction were measured, specifically serum creatinine, aspartate aminotransferase, and gamma-glutamyl-transferase, creatinine clearance, urine flow, and fractional excretion of sodium. Kidney PPARgamma1 mRNA levels were determined by reverse transcriptase-polymerase chain reaction. RESULTS: Pretreatment with LPS significantly attenuated all markers of renal injury and dysfunction caused by I/R. Most notably, GW9662 abolished the protective effects of LPS. Additionally, I/R caused an up-regulation of kidney PPARgamma1 mRNA levels compared to sham animals, which were unchanged in rats pretreated with LPS. CONCLUSION: We document here for the first time that endogenous ligands of PPARgamma may contribute to the protection against renal I/R injury afforded by LPS pretreatment in the rat.

Impaired glucose homeostasis and mitochondrial abnormalities in offspring of rats fed a fat-rich diet in pregnancy.

We previously reported that prenatal and suckling exposure to a maternal diet rich in animal fat leads to cardiovascular dysfunction in young adult rat offspring with subsequent development of dyslipidemia and hyperglycemia. We have further investigated glucose homeostasis in adult female offspring by euglycemic-hyperinsulinemic clamp and by dynamic assessment of glucose-stimulated insulin secretion in isolated, perifused pancreatic islet cells. Additionally, given the link between reduced mitochondrial DNA (mtDNA) content and the development of type 2 diabetes mellitus, we have measured mtDNA in organs from young adult animals. Sprague-Dawley rats were fed a diet rich in animal fat or normal chow throughout pregnancy and weaning. Infusion of insulin (5 mU.kg(-1).min(-1)) resulted in a higher steady-state plasma insulin concentration in 1-year-old offspring of fat-fed dams (OHF, n = 4) vs. offspring of control dams (OC, n = 4, P < 0.01). Glucose-stimulated insulin secretion in isolated islets from 9-mo-old OHF was significantly reduced compared with OC (n = 4, P < 0.05). Transmission electron micrography showed altered insulin secretory granule morphology in OHF pancreatic beta-cells. Kidney mtDNA was reduced in 3-mo-old OHF [16S-to-18S gene ratio: OC (n = 10) 1.05 +/- 0.19 vs. OHF (n = 10) 0.66 +/- 0.06, P < 0.05]. At 6 mo, gene chip microarray of OHF aorta showed reduced expression of the mitochondrial genome. Prenatal and suckling exposure to a diet rich in animal fat leads to whole body insulin resistance and pancreatic beta-cell dysfunction in adulthood, which is preceded by reduced tissue mtDNA content and altered mitochondrial gene expression.

Hypertrophic effects of urocortin homologous peptides are mediated via activation of the Akt pathway.

The UCN homologues SCP and SRP bind specifically to the CRFR2 receptor, whereas UCN binds to both CRFR1 and CRFR2. We have previously demonstrated that all three peptides are cardioprotective, and both the Akt and MAPK p42/44 pathways are essential for this effect. Here we tested the hypertrophic effects of these peptides. We examined the effects of the peptides on cell area, protein synthesis, and induction of the natriuretic peptides ANP and BNP. All three peptides were able to increase all the markers of hypertrophy examined, with SCP being the most potent of the three, followed by UCN and SRP last. In addition, we provide a mechanism of action for the three peptides and show that Akt phosphorylation is important for their hypertrophic action, whereas MAPK p42/44 is not involved in this effect.

STAT-1 facilitates the ATM activated checkpoint pathway following DNA damage.

STAT-1 plays a role in mediating stress responses to various stimuli and has also been implied to be a tumour suppressor. Here, we report that STAT-1-deficient cells have defects both in intra-S-phase and G2-M checkpoints in response to DNA damage. Interestingly, STAT-1-deficient cells showed reduced Chk2 phosphorylation on threonine 68 (Chk2(-T68)) following DNA damage, suggesting that STAT-1 might function in the ATM-Chk2 pathway. Moreover, the defects in Chk2(-T68) phosphorylation in STAT-1-deficient cells also correlated with reduced degradation of Cdc25A compared with STAT-1-expressing cells after DNA damage. We also show that STAT-1 is required for ATM-dependent phosphorylation of NBS1 and p53 but not for BRCA1 or H2AX phosphorylation following DNA damage. Expression levels of BRCT mediator/adaptor proteins MDC1 and 53BP1, which are required for ATM-mediated pathways, are reduced in cells lacking STAT-1. Enforced expression of MDC1 into STAT-1-deficient cells restored ATM-mediated phosphorylation of downstream substrates. These results imply that STAT-1 plays a crucial role in the DNA-damage-response by regulating the expression of 53BP1 and MDC1, factors known to be important for mediating ATM-dependent checkpoint pathways.

BAG-1 proteins protect cardiac myocytes from simulated ischemia/reperfusion-induced apoptosis via an alternate mechanism of cell survival independent of the proteasome.

BAG-1 (Bcl-2-associated athanogene-1) proteins interact with the HSC70 and HSP70 heat shock proteins and have been proposed to promote cell survival by coordinating the function of these chaperones with the proteasome to facilitate protein degradation. Consistent with this proposal, previous analyses in cancer cells have demonstrated that BAG-1 requires protein domains important for HSC70/HSP70 and proteasome binding in order to interfere with the growth inhibition induced by heat shock (Townsend, P. A., Cutress, R. I., Sharp, A., Brimmell, M., and Packham, G. (2003) Cancer Res., 63, 4150-4157). Moreover, cellular stress triggered the relocalization of the cytoplasmic BAG-1S (approximately 36 kDa) isoform to the nucleus, and both BAG-1S and the constitutively nuclear localized BAG-1L (approximately 50 kDa) isoform suppressed heat shock-induced apoptosis to the same extent, suggesting a critical role in the nucleus. Because ischemia (I) and reperfusion (R) are important stress signals in acute and chronic heart disease, we have examined the expression and function of BAG-1 proteins in primary cardiac myocytes (CMs) and the Langendorff-perfused intact heart. The expression of both BAG-1 isoforms, BAG-1S and BAG-1L, was rapidly induced following ischemia in rat CM, and this was maintained during subsequent reperfusion. In control hearts, BAG-1S and BAG-1L were readily detectable in both the nucleus and the cytoplasm. However, BAG-1S did not relocate to the nucleus following simulated I/R. BAG-1 interacted with both RAF-1 and HSC70 in CMs and the whole heart, and binding to HSC70 was increased following I/R. Overexpression of the human BAG-1S and BAG-1 M isoforms significantly reduced CM apoptosis following simulated I/R. By contrast, BAG-1L or BAG-1S fused to a heterologous nuclear localization sequence failed to protect CM. Finally, overexpression of BAG-1 deletion and point mutants unable to bind HSC70/HSP70 failed to offer cardioprotection. Surprisingly, a deletion mutant lacking the N-terminal ubiquitin-like domain, which mediates interaction with the proteasome, still promoted cardioprotection. Therefore, BAG-1 has a novel cardioprotective role, mediated via association with HSC70/HSP70, which is critical upon cytoplasmic localization but independent of the BAG-1 ubiquitin-like domain. Our studies demonstrate that BAG-1 can influence cellular response to stress by multiple mechanisms, potentially influenced by the cell type and nature of the stress signal.

The cardioprotective effect of urocortin during ischaemia/reperfusion involves the prevention of mitochondrial damage.

We have previously shown, using Affymetrix gene chip technology, that urocortin induces the expression of several diverse genes in cardiac myocytes. An ATP sensitive inwardly rectifying potassium channel, Katp (Kir6.1), the enzyme calcium independent phospholipase A2 (iPLA2), and protein kinase C epsilon (PKCepsilon) and that these genes are involved in the cardioprotective mechanism of action of urocortin. Here we demonstrate that these gene products are localized to cardiac myocyte mitochondria and for the first time show that urocortin protects cardiac myocytes from ischaemia/reperfusion induced cell death by preventing mitochondrial damage. Using pharmacological agents to Katp channels and iPLA2 and synthetic peptide inhibitors of PKCepsilon, we go on to demonstrate that these three gene products are involved in the urocortin induced protection of cardiac myocyte mitochondria. These proteins may interact at the mitochondria to produce the protective effect.