Enhanced contractility of small blood vessels in JNK knockout mice

Biological Properties of JNK3 and Its Function in Neurons, Astrocytes, Pancreatic β-Cells and Cardiovascular Cells

JNK is a protein kinase, which induces transactivation of c-jun. The three isoforms of JNK, JNK1, JNK2, and JNK3, are encoded by three distinct genes. JNK1 and JNK2 are expressed ubiquitously throughout the body. By contrast, the expression of JNK3 is limited and observed mainly in the brain, heart, and testes. Concerning the biological properties of JNKs, the contribution of upstream regulators and scaffold proteins plays an important role in the activation of JNKs. Since JNK signaling has been described as a form of stress-response signaling, the contribution of JNK3 to pathophysiological events, such as stress response or cell death including apoptosis, has been well studied. However, JNK3 also regulates the physiological functions of neurons and non-neuronal cells, such as development, regeneration, and differentiation/reprogramming. In this review, we shed light on the physiological functions of JNK3. In addition, we summarize recent advances in the knowledge regarding interactions between JNK3 and cellular reprogramming.

Estrogen increases expression of vascular alpha 2C adrenoceptor through the cAMP/Epac/JNK/AP-1 pathway and potentiates cold-induced vasoconstriction

Cutaneous cold-induced vasoconstriction is a normal physiological reaction mediated by alpha 2C-adrenergic receptors (α_2C-ARs) expressed in vascular smooth muscle cells (VSMCs). When this reaction is exaggerated, Raynaud's phenomenon (RP) ensues. RP is more prevalent in females compared to age-matched men. We previously established that 17-β estradiol (estrogen) upregulates α_2C-ARs in human VSMCs via a cAMP/Epac/Rap pathway. We also showed that cAMP acts through JNK to increase α_2C-AR expression. However, whether estrogen employs JNK to regulate α_2C-AR is not investigated. Knowing that the α_2C-AR promoter harbors an activator protein-1 (AP-1) binding site that can be potentially activated by JNK, we hypothesized that estrogen regulates α_2C-AR expression through an Epac/JNK/AP-1 pathway. Our results show that estrogen (10^-10 M) activated JNK in human VSMCs extracted from cutaneous arterioles. Pretreatment with ESI09 (10 μM; an Epac inhibitor), abolished estrogen-induced JNK activation. In addition, pre-treatment with SP600125 (3 μM; a JNK specific inhibitor) abolished estrogen-induced expression of α_2C-AR. Importantly, estrogen-induced activation of α_2C-AR promoter was attenuated with SP600125. Moreover, transient transfection of VSMCs with an Epac dominant negative mutant (Epac-DN) abolished estrogen-induced activation of α_2C-AR promoter. However, co-transfection of constitutively active JNK mutant overrode the inhibitory effect of Epac-DN on α_2C-AR promoter. Moreover, estrogen caused a concentration-dependent increase in the activity of AP-1-driven reporter construct. Mutation of AP-1 site in the α_2C-AR promoter abolished its activation by estrogen. This in vitro estrogen-increased α_2C-AR expression was mirrored by an increase in the ex vivo functional responsiveness of arterioles. Indeed, estrogen potentiated α_2C-AR-mediated cold-induced vasoconstriction, which was abolished by SP600125. Collectively, these results indicate that estrogen upregulates α_2C-AR expression via an EPAC-mediated JNK/AP-1- dependent mechanism. These results provide an insight into the mechanism by which exaggerated cold-induced vasoconstriction occurs in estrogen-replete females and identify Epac and JNK as potential targets for the treatment of RP.

Increased expression of desmin and vimentin reduces bladder smooth muscle contractility via JNK2

Bladder dysfunction is associated with the overexpression of the intermediate filament (IF) proteins desmin and vimentin in obstructed bladder smooth muscle (BSM). However, the mechanisms by which these proteins contribute to BSM dysfunction are not known. Previous studies have shown that desmin and vimentin directly participate in signal transduction. In this study, we hypothesized that BSM dysfunction associated with overexpression of desmin or vimentin is mediated via c-Jun N-terminal kinase (JNK). We employed a model of murine BSM tissue in which increased expression of desmin or vimentin was induced by adenoviral transduction to examine the sufficiency of increased IF protein expression to reduce BSM contraction. Murine BSM strips overexpressing desmin or vimentin generated less force in response to KCl and carbachol relative to the levels in control murine BSM strips, an effect associated with increased JNK2 phosphorylation and reduced myosin light chain (MLC20 ) phosphorylation. Furthermore, desmin and vimentin overexpressions did not alter BSM contractility and MLC20 phosphorylation in strips isolated from JNK2 knockout mice. Pharmacological JNK2 inhibition produced results qualitatively similar to those caused by JNK2 knockout. These findings suggest that inhibition of JNK2 may improve diminished BSM contractility associated with obstructive bladder disease.

N-Methyl-D-Aspartate Receptor Signaling and Function in Cardiovascular Tissues

Excellent reviews on central N-methyl-D-aspartate receptor (NMDAR) signaling and function in cardiovascular regulating neuronal pools have been reported. However, much less attention has been given to NMDAR function in peripheral tissues, particularly the heart and vasculature, although a very recent review discusses such function in the kidney. In this short review, we discuss the NMDAR expression and complexity of its function in cardiovascular tissues. In conscious (contrary to anesthetized) rats, activation of the peripheral NMDAR triggers cardiovascular oxidative stress through the PI3K-ERK1/2-NO signaling pathway, which ultimately leads to elevation in blood pressure. Evidence also implicates Ca release, in the peripheral NMDAR-mediated pressor response. Despite evidence of circulating potent ligands (eg, D-aspartate and L-aspartate, L-homocysteic acid, and quinolinic acid) and also their coagonist (eg, glycine or D-serine), the physiological role of peripheral cardiovascular NMDAR remains elusive. Nonetheless, the cardiovascular relevance of the peripheral NMDAR might become apparent when its signaling is altered by drugs, such as alcohol, which interact with the NMDAR or its downstream signaling mechanisms.

Death receptors DR6 and TROY regulate brain vascular development

Signaling events that regulate central nervous system (CNS) angiogenesis and blood-brain barrier (BBB) formation are only beginning to be elucidated. By evaluating the gene expression profile of mouse vasculature, we identified DR6/TNFRSF21 and TROY/TNFRSF19 as regulators of CNS-specific angiogenesis in both zebrafish and mice. Furthermore, these two death receptors interact both genetically and physically and are required for vascular endothelial growth factor (VEGF)-mediated JNK activation and subsequent human brain endothelial sprouting in vitro. Increasing beta-catenin levels in brain endothelium upregulate DR6 and TROY, indicating that these death receptors are downstream target genes of Wnt/beta-catenin signaling, which has been shown to be required for BBB development. These findings define a role for death receptors DR6 and TROY in CNS-specific vascular development.

Role of c-Jun N-terminal kinase in the regulation of vascular tone

The c-Jun N-terminal kinases (JNKs) belong to the mitogen-activated protein kinases superfamily, which play an important role in the pathogenesis of cardiovascular and metabolic diseases. However, it is still unclear whether JNK participates in the regulation of vascular tone. We investigated the effect of JNK inhibitors on vascular reactivity in aortic rings in organ bath and on angiotensin (Ang) II-induced pressor responses in vivo in Sprague-Dawley (SD) rats. In aortic rings from SD rats, KCl, norepinephrine (NE), Ang II, or endothelin 1 (ET)-1 induced a dose-dependent vasoconstriction. Preincubation with the JNK inhibitor SP600125 (20 micromol/L) slightly inhibited KCl-induced vasoconstriction (Emax: -19%) and markedly inhibited vasoconstriction to NE (-42%), Ang II (-54%), and ET-1 (-42%). SP600125 induced a dose-dependent relaxation in the NE-preconstricted aortic rings (-54%) but exerted minimal relaxation in the KCI-preconstriction rings. To exclude the nonspecific effect of SP600125, we performed additional experiments using JNK peptide inhibitor 1, L-stereoisomer (L-JNKI1), a cell-permeable peptide inhibitor specific for JNK. Compared to SP600125, L-JNKI1 (20 micromol/L) had a smaller but still significant inhibitory effect on NE-induced vasoconstriction (-18%) and did not inhibit KCI-induced vasoconstriction. Next, we investigated the effect of L-JNKI1 (5 mg/kg intravenously [IV]) in vivo on Ang II-induced pressor responses in SD rats. Ang II induces a dose-dependent increase in systolic blood pressure and L-JNKI1 slightly attenuated the Ang II-induced pressor response. These results suggest that JNK signaling plays a role in the regulation of vascular tone.

Neuronostatin inhibits cardiac contractile function via a protein kinase A- and JNK-dependent mechanism in murine hearts

Neuronostatin, a newly identified peptide hormone sharing the same precursor with somatostatin, exerts multiple pharmacological effects in gastrointestinal tract, hypothalamus, and cerebellum. However, the cardiovascular effect of neuronostatin is unknown. The aim of this study was to elucidate the impact of neuronostatin on cardiac contractile function in murine hearts and isolated cardiomyocytes. Short-term exposure of neuronostatin depressed left ventricular developed pressure (LVDP), maximal velocity of pressure development (+/-dP/dt), and heart rate in Langendorff heart preparation. Consistently, neuronostatin inhibited peak shortening (PS) and maximal velocity of shortening/relengthening (+/-dL/dt) without affecting time-to-PS (TPS) and time-to-90% relengthening (TR(90)) in cardiomyocytes. The neuronostatin-elicited cardiomyocyte mechanical responses were mimicked by somatostatin, the other posttranslational product of preprosomatostatin. Furthermore, the neuronostatin-induced cardiomyocyte mechanical effects were ablated by the PKA inhibitor H89 (1 microM) and the Jun N-terminal kinase (JNK) inhibitor SP600125 (20 microM). The PKC inhibitor chelerythrine (1 microM) failed to alter neuronostatin-induced cardiomyocyte mechanical responses. To the contrary, chelerythrine, but not H89, abrogated somatostatin-induced cardiomyocyte contractile responses. Our results also showed enhanced c-fos and c-jun expression in response to neuronostatin exposure (0.5 to 2 h). Taken together, our data suggest that neuronostatin is a peptide hormone with overt cardiac depressant action. The neuronostatin-elicited cardiac contractile response appears to be mediated, at least in part, through a PKA- and/or JNK-dependent mechanism.