The cardioprotective effects of urocortin are mediated via activation of the Src tyrosine kinase-STAT3 pathway

Urocortin 3 overexpression reduces ER stress and heat shock response in 3T3-L1 adipocytes

The neuropeptide urocortin 3 (UCN3) has a beneficial effect on metabolic disorders, such as obesity, diabetes, and cardiovascular disease. It has been reported that UCN3 regulates insulin secretion and is dysregulated with increasing severity of obesity and diabetes. However, its function in the adipose tissue is unclear. We investigated the overexpression of UCN3 in 3T3-L1 preadipocytes and differentiated adipocytes and its effects on heat shock response, ER stress, inflammatory markers, and glucose uptake in the presence of stress-inducing concentrations of palmitic acid (PA). UCN3 overexpression significantly downregulated heat shock proteins (HSP60, HSP72 and HSP90) and ER stress response markers (GRP78, PERK, ATF6, and IRE1α) and attenuated inflammation (TNFα) and apoptosis (CHOP). Moreover, enhanced glucose uptake was observed in both preadipocytes and mature adipocytes, which is associated with upregulated phosphorylation of AKT and ERK but reduced p-JNK. Moderate effects of UCN3 overexpression were also observed in the presence of 400 μM of PA, and macrophage conditioned medium dramatically decreased the UCN3 mRNA levels in differentiated 3T3-L1 cells. In conclusion, the beneficial effects of UCN3 in adipocytes are reflected, at least partially, by the improvement in cellular stress response and glucose uptake and attenuation of inflammation and apoptosis.

Changes in Musculoskeletal System and Metabolism in Osteoporotic Rats Treated With Urocortin

Objective: In aging population, postmenopausal osteoporosis and decline of musculoskeletal function, referred to as "frailty syndrome" lead to loss of bone and muscle, causing falls, and fall-related injuries. To limit the impact of this portentous duo, simultaneous treatment of both is needed. Urocortin (UCN) has been reported to improve osteoporotic bone properties while its effect on muscle has not been addressed yet. Design and Methods: We aimed to investigate the effect of urocortin in vivo on skeletal muscle structure in osteopenic rats. Sixty Sprague-Dawley rats were divided into five groups: four were ovariectomized (OVX) and one underwent sham operation (SHAM). One ovariectomized group was left untreated (OVX), while one was treated with urocortin s.c. in 3 μg/kg body weight (bw) (OVX+UCN low), one with 30 μg/kg (OVX+UCN high), while one group was treated with estradiol orally (OVX+E: 0.2 mg/kg bw), each for 35 days. Mm. gastrocnemius, longissimus, and soleus were isolated and capillary density as well as diameters of type I and II fibers were measured. In addition, we examined the effect of UCN on tibia using biomechanical, micro-CT and ashing analysis and investigated the blood serum. Results: We demonstrated a positive effect of UCN on M. soleus, in which fiber diameter was positively influenced. The biomechanical and structural parameters of bone were not changed in UCN treated rats. The higher cholesterol, glucose and triglyceride levels in the "UCN high" group raise concern about this treatment. Conclusions: Our results portray urocortin as a substance that can be assessed for future therapeutic treatments of estrogen deficiency. New and Noteworthy: Urocortin has a positive effect on M. soleus (diameter). Urocortin raises serum cholesterol and triglyceride levels. Bone tissue was not affected by UCN.

CRF1 Receptor Signaling via the ERK1/2-MAP and Akt Kinase Cascades: Roles of Src, EGF Receptor, and PI3-Kinase Mechanisms

In the present study, we determined the cellular regulators of ERK1/2 and Akt signaling pathways in response to human CRF₁ receptor (CRF₁R) activation in transfected COS-7 cells. We found that Pertussis Toxin (PTX) treatment or sequestering Gβγ reduced CRF₁R-mediated activation of ERK1/2, suggesting the involvement of a G_i-linked cascade. Neither G_s/PKA nor G_q/PKC were associated with ERK1/2 activation. Besides, CRF induced EGF receptor (EGFR) phosphorylation at Tyr¹⁰⁶⁸, and selective inhibition of EGFR kinase activity by AG1478 strongly inhibited the CRF₁R-mediated phosphorylation of ERK1/2, indicating the participation of EGFR transactivation. Furthermore, CRF-induced ERK1/2 phosphorylation was not altered by pretreatment with batimastat, GM6001, or an HB-EGF antibody indicating that metalloproteinase processing of HB-EGF ligands is not required for the CRF-mediated EGFR transactivation. We also observed that CRF induced Src and PYK2 phosphorylation in a Gβγ-dependent manner. Additionally, using the specific Src kinase inhibitor PP2 and the dominant-negative-SrcYF-KM, it was revealed that CRF-stimulated ERK1/2 phosphorylation depends on Src activation. PP2 also blocked the effect of CRF on Src and EGFR (Tyr⁸⁴⁵) phosphorylation, further demonstrating the centrality of Src. We identified the formation of a protein complex consisting of CRF₁R, Src, and EGFR facilitates EGFR transactivation and CRF₁R-mediated signaling. CRF stimulated Akt phosphorylation, which was dependent on G_i/βγ subunits, and Src activation, however, was only slightly dependent on EGFR transactivation. Moreover, PI3K inhibitors were able to inhibit not only the CRF-induced phosphorylation of Akt, as expected, but also ERK1/2 activation by CRF suggesting a PI3K dependency in the CRF₁R ERK signaling. Finally, CRF-stimulated ERK1/2 activation was similar in the wild-type CRF₁R and the phosphorylation-deficient CRF₁R-Δ386 mutant, which has impaired agonist-dependent β-arrestin-2 recruitment; however, this situation may have resulted from the low β-arrestin expression in the COS-7 cells. When β-arrestin-2 was overexpressed in COS-7 cells, CRF-stimulated ERK1/2 phosphorylation was markedly upregulated. These findings indicate that on the base of a constitutive CRF₁R/EGFR interaction, the G_i/βγ subunits upstream activation of Src, PYK2, PI3K, and transactivation of the EGFR are required for CRF₁R signaling via the ERK1/2-MAP kinase pathway. In contrast, Akt activation via CRF₁R is mediated by the Src/PI3K pathway with little contribution of EGFR transactivation.

The type VI adenylyl cyclase protects cardiomyocytes from β-adrenergic stress by a PKA/STAT3-dependent pathway

BACKGROUND

The type VI adenylyl cyclase (AC6) is a main contributor of cAMP production in the heart. The amino acid (aa) sequence of AC6 is highly homologous to that of another major cardiac adenylyl cyclase, AC5, except for its N-terminus (AC6-N, aa 1-86). Activation of AC6, rather than AC5, produces cardioprotective effects against heart failure, while the underlying mechanism remains to be unveiled. Using an AC6-null (AC6^-/-) mouse and a knockin mouse with AC6-N deletion (AC6 ^ΔN/ΔN), we aimed to investigate the cardioprotective mechanism of AC6 in the heart.

METHODS

Western blot analysis and immunofluorescence staining were performed to determine the intracellular distribution of AC6, AC6-ΔN (a truncated AC6 lacking the first 86 amino acids), and STAT3 activation. Activities of AC6 and AC6-ΔN in the heart were assessed by cAMP assay. Apoptosis of cardiomyocytes were evaluated by the TUNEL assay and a propidium iodine-based survival assay. Fibrosis was examined by collagen staining.

RESULTS

Immunofluorescence staining revealed that cardiac AC6 was mainly anchored on the sarcolemmal membranes, while AC6-ΔN was redistributed to the sarcoplasmic reticulum. AC6^ΔN/ΔN and AC6^-/- mice had more apoptotic myocytes and cardiac remodeling than WT mice in experimental models of isoproterenol (ISO)-induced myocardial injury. Adult cardiomyocytes isolated from AC6^ΔN/ΔN or AC6^-/- mice survived poorly after exposure to ISO, which produced no effect on WT cardiomyocytes under the condition tested. Importantly, ISO treatment induced cardiac STAT3 phosphorylation/activation in WT mice, but not in AC6^ΔN/ΔN and AC6^-/- mice. Pharmacological blockage of PKA-, Src-, or STAT3- pathway markedly reduced the survival of WT myocytes in the presence of ISO, but did not affect those of AC6^ΔN/ΔN and AC6^-/- myocytes, suggesting an important role of AC6 in mediating cardioprotective action through the activation of PKA-Src-STAT3-signaling.

CONCLUSIONS

Collectively, AC6-N controls the anchorage of cardiac AC6 on the sarcolemmal membrane, which enables the coupling of AC6 with the pro-survival PKA-STAT3 pathway. Our findings may facilitate the development of novel therapies for heart failure.

miR-125a, miR-139 and miR-324 contribute to Urocortin protection against myocardial ischemia-reperfusion injury

Urocortin 1 and 2 (Ucn-1 and Ucn-2) have established protective actions against myocardial ischemia-reperfusion (I/R) injuries. However, little is known about their role in posttranscriptional regulation in the process of cardioprotection. Herein, we investigated whether microRNAs play a role in urocortin-induced cardioprotection. Administration of Ucn-1 and Ucn-2 at the beginning of reperfusion significantly restored cardiac function, as evidenced ex vivo in Langendorff-perfused rat hearts and in vivo in rat subjected to I/R. Experiments using microarray and qRT-PCR determined that the addition of Ucn-1 at reperfusion modulated the expression of several miRNAs with unknown role in cardiac protection. Ucn-1 enhanced the expression of miR-125a-3p, miR-324-3p; meanwhile it decreased miR-139-3p. Similarly, intravenous infusion of Ucn-2 in rat model of I/R mimicked the effect of Ucn-1 on miR-324-3p and miR-139-3p. The effect of Ucn-1 involves the activation of corticotropin-releasing factor receptor-2, Epac2 and ERK1/2. Moreover, the overexpression of miR-125a-3p, miR-324-3p and miR-139-3p promoted dysregulation of genes expression involved in cell death and apoptosis (BRCA1, BIM, STAT2), in cAMP and Ca²⁺ signaling (PDE4a, CASQ1), in cell stress (NFAT5, XBP1, MAP3K12) and in metabolism (CPT2, FoxO1, MTRF1, TAZ). Altogether, these data unveil a novel role of urocortin in myocardial protection, involving posttranscriptional regulation with miRNAs.

Urocortin-1 Mediated Cardioprotection Involves XIAP and CD40-Ligand Recovery: Role of EPAC2 and ERK1/2

Aims

Urocortin-1 (Ucn-1) is an endogenous peptide that protects heart from ischemia and reperfusion (I/R) injuries. Ucn-1 is known to prevent cardiac cell death, but its role in the transcription of specific genes related to survival signaling pathway has not been fully defined. The aim of this study was to investigate the molecular signaling implicated in the improvement of cardiac myocytes survival induced by Ucn-1.

Methods and Results

Ucn-1 administration before ischemia and at the onset of reperfusion, in rat hearts perfused in Langendorff system, fully recovered heart contractility and other hemodynamic parameters. Ucn-1 enhanced cell viability and decreased lactate dehydrogenase (LDH) release in adult cardiac myocytes subjected to simulated I/R. Annexin V-FITC/PI staining indicated that Ucn-1 promoted cell survival and decreased cell necrosis through Epac2 (exchange protein directly activated by cAMP) and ERK1/2 (extracellular signal–regulated kinases 1/2) activation. We determined that Ucn-1 shifted cell death from necrosis to apoptosis and activated caspases 9 and 3/7. Furthermore, mini-array, RT-qPCR and protein analyses of apoptotic genes showed that Ucn-1 upregulated the expression of CD40lg, Xiap and BAD in cells undergoing I/R, involving Epac2 and ERK1/2 activation.

Conclusions

Our data indicate that Ucn-1 efficiently protected hearts from I/R damage by increasing the cell survival and stimulated apoptotic genes, CD40lg, Xiap and BAD, overexpression through the activation of Epac2 and ERK1/2.

Cyclic stretch-induced TGF-β1 and fibronectin expression is mediated by β1-integrin through c-Src- and STAT3-dependent pathways in renal epithelial cells

Extracellular matrix (ECM) proteins, including fibronectin, may contribute to the early development and progression of renal interstitial fibrosis associated with chronic renal disease. Recent studies showed that β1-integrin is associated with the development of renal fibrosis in a murine model of unilateral ureteral obstruction (UUO). However, the molecular events responsible for β1-integrin-mediated signaling, following UUO, have yet to be determined. In this study, we investigated the mechanism by which mechanical stretch, an in vitro model for chronic obstructive nephropathy, regulates fibronectin and transforming growth factor-β1 (TGF-β1) expression in cultured human proximal tubular epithelium (HK-2) cells. Mechanical stretch upregulated fibronectin and TGF-β1 expression and activated signal transducer and transcription factor 3 (STAT3) in a time-dependent manner. Stretch-induced fibronectin and TGF-β1 were suppressed by a STAT3 inhibitor, S3I-201, and by small interfering RNA (siRNA) targeting human STAT3 (STAT3 siRNA). Similarly, fibronectin and TGF-β1 expression and STAT3 activation induced by mechanical stretch were suppressed by the Src family kinase inhibitor PP2 and by transfection of HK-2 cells with a dominant-negative mutant of c-Src (DN-Src), whereas PP3, an inactive analog of PP2, had no significant effect. Furthermore, mechanical stretch resulted in increased β1-integrin mRNA and protein levels in HK-2 cells. Furthermore, neutralizing antibody against β1-integrin and silencing of β1-integrin expression with siRNAs resulted in decreased c-Src and STAT3 activation and TGF-β1 and fibronectin expression evoked by mechanical stretch. This work demonstrates, for the first time, a role for β1-integrin in stretch-induced renal fibrosis through the activation of c-Src and STAT3 signaling pathways.