Autoregulatory Control of Smooth Muscle Myosin Light Chain Kinase Promoter by Notch Signaling

Loss of Jagged1 in mature endothelial cells causes vascular dysfunction with alterations in smooth muscle phenotypes

BACKGROUND

Notch signaling is an evolutionarily conserved pathway that functions via direct cell-cell contact. The Notch ligand Jagged1 (Jag1) has been extensively studied in vascular development, particularly for its role in smooth muscle cell maturation. Endothelial cell-expressed Jag1 is essential for blood vessel formation by signaling to nascent vascular smooth muscle cells and promoting their differentiation. Given the established importance of Jag1 in endothelial cell/smooth muscle crosstalk during development, we sought to determine the extent of this communication in the adult vasculature for blood vessel function and homeostasis.

METHODS

We conditionally deleted Jag1 in endothelial cells of adult mice and examined the phenotypic consequences on smooth muscle cells of the vasculature.

RESULTS

Our results show that genetic loss of Jag1 in endothelial cells has a significant impact on Notch signaling and vascular smooth muscle function in mature blood vessels. Endothelial cell-specific deletion of Jag1 causes a concomitant loss of JAG1 and NOTCH3 expression in vascular smooth muscle cells, resulting in a transition to a less differentiated state. Aortic vascular smooth muscle cells isolated from the endothelial cell-specific Jag1 deficient mice retain an altered phenotype in culture with fixed changes in gene expression and reduced Notch signaling. Utilizing comparative RNA-sequence analysis, we found that Jag1 deficiency preferentially affects extracellular matrix and adhesion protein gene expression. Vasoreactivity studies revealed a reduced contractile response and impaired agonist-induced relaxation in endothelial cell Jag1-deficient aortas compared to controls.

CONCLUSIONS

These data are the first to demonstrate that Jag1 in adult endothelial cells is required for the regulation and homeostasis of smooth muscle cell function in arterial vessels partially through the autoregulation of Notch signaling and cell matrix/adhesion components in smooth muscle cells.

Phenylephrine induces relaxation of longitudinal strips from small arteries of goat legs

Alpha adrenergic stimulation is known to produce vasoconstriction. We have earlier shown that, in spiral strips of small arteries Phenylephrine (PE) caused vasorelaxation under high nitric oxide (NO) environment. However, on further experimentation it was realized that the PE-induced vasorelaxant response occurred only with longitudinal strips of small arteries even under normal NO environment while circular strips showed contraction with PE even under high NO environment. Such PE-induced vasorelaxation of longitudinal strips was blocked by Phentolamine, an alpha-adrenergic receptor blocker. On delineation of specific receptor subtype, PE-induced relaxation was found to be mediated through alpha 1D receptor. However, this phenomenon is specific to small artery, as longitudinal smooth muscle of aorta showed only contractile response to adrenergic stimulation. There is no prior report of longitudinal smooth muscle in small artery up to our knowledge. The results of this study and histological examination of vessel sections suggest the presence of longitudinal smooth muscle in small artery and their relaxant response to alpha adrenergic stimulation is a novel phenomenon.

Notch signaling regulates arterial vasoreactivity through opposing functions of Jagged1 and Dll4 in the vessel wall

Functional interactions between endothelial cells (ECs) and smooth muscle cells (SMCs) in the arterial wall are necessary for controlling vasoreactivity that underlies vascular resistance and tone. Key signaling pathways converge on the phosphorylation of myosin light chain (p-MLC), the molecular signature of force production in SMCs, through coordinating the relative activities of myosin light chain kinase (MLCK) and myosin phosphatase (MP). Notch signaling in the vessel wall serves critical roles in arterial formation and maturation and has been implicated in arterial vasoregulation. In this report, we hypothesized that Notch signaling through ligands Jagged1 (in SMCs) and delta-like protein-4 (Dll4; in ECs) regulates vasoreactivity via homotypic (SMC-SMC) and heterotypic (EC-SMC) cell interactions. Using ligand induction assays, we demonstrated that Jagged1 selectively induced smooth muscle MLCK gene expression and p-MLC content while inhibiting MP function (i.e., increased Ca²⁺ sensitization) in a Rho kinase II-dependent manner. Likewise, selective deficiency of smooth muscle Jagged1 in mice resulted in MLCK and p-MLC loss, reduced Ca²⁺ sensitization, and impaired arterial force generation measured by myography. In contrast, smooth muscle Notch signaling triggered by Dll4 increased expression of MP-targeting subunit 1 (MYPT1; the MP regulatory subunit), whereas arteries from endothelial Dll4-deficient mice featured reduced MYPT1 levels, enhanced force production, and impaired relaxation independent of endothelium-derived nitric oxide signaling. Taken together, this study identifies novel opposing vasoregulatory functions for ligand-specific Notch signaling in the vessel wall, underscoring instructional signaling between ECs and SMCs and suggesting that Notch signals might behave as a "rheostat" in arterial tone control. NEW & NOTEWORTHY The present study unveils novel roles for ligand-specific Notch signaling in arterial function. Smooth muscle Jagged1 and endothelial cell delta-like protein-4 ligands exhibit selective regulation of myosin light chain kinase and myosin phosphatase-targeting subunit 1/myosin phosphatase, respectively, providing a mechanistic link through which Notch signals modulate contractile activities in vascular smooth muscle. These findings may inform vascular derangements observed in human syndromes of Notch signaling deficiency while offering fundamental molecular insights into arterial physiological function.

Mechanosensitivity of Jagged-Notch signaling can induce a switch-type behavior in vascular homeostasis

Hemodynamic forces and Notch signaling are both known as key regulators of arterial remodeling and homeostasis. However, how these two factors integrate in vascular morphogenesis and homeostasis is unclear. Here, we combined experiments and modeling to evaluate the impact of the integration of mechanics and Notch signaling on vascular homeostasis. Vascular smooth muscle cells (VSMCs) were cyclically stretched on flexible membranes, as quantified via video tracking, demonstrating that the expression of Jagged1, Notch3, and target genes was down-regulated with strain. The data were incorporated in a computational framework of Notch signaling in the vascular wall, where the mechanical load was defined by the vascular geometry and blood pressure. Upon increasing wall thickness, the model predicted a switch-type behavior of the Notch signaling state with a steep transition of synthetic toward contractile VSMCs at a certain transition thickness. These thicknesses varied per investigated arterial location and were in good agreement with human anatomical data, thereby suggesting that the Notch response to hemodynamics plays an important role in the establishment of vascular homeostasis.

ML-7 attenuates airway inflammation and remodeling via inhibiting the secretion of Th2 cytokines in mice model of asthma

Previous studies have indicated that smooth muscle myosin light chain kinase (MLCK) has a prominent role in the regulation of smooth muscle contraction, which tends to be upregulated in asthma. In recent years, numerous studies have reported that MLCK is intimately connected with the immunoregulatory mechanism of T cells. The imbalance of T helper type 1 cells (Th1)/Th2 constitutes the immune-associated pathological basis of chronic asthma. Th2-associated cytokines, including interleukin-4, −5, −13, −25 and −33, are involved in airway inflammation, hyperresponsiveness and remodeling, which leads to a progressive decline in lung function. The purpose of the present study was to verify whether inhibition of bronchial MLCK attenuated the expression Th2-associated cytokines in asthmatic mice, including the above-mentioned ones. Female BALB/c mice were used to establish an ovalbumin (OVA)-induced model of asthma, of which one group was treated with the MLCK inhibitor (5-iodonaphthalene-1-sulfonyl) homopiperazine (ML-7). The inhibitor of MLCK, ML-7 attenuated airway inflammation and remodeling by reducing inflammatory cell infiltration and the secretion of Th2 cytokines in mice model of asthma, which may represent a promising therapeutic strategy for asthma.

Myosin Light Chain Kinase MYLK1: Anatomy, Interactions, Functions, and Regulation

This review discusses and summarizes the results of molecular and cellular investigations of myosin light chain kinase (MLCK, MYLK1), the key regulator of cell motility. The structure and regulation of a complex mylk1 gene and the domain organization of its products is presented. The interactions of the mylk1 gene protein products with other proteins and posttranslational modifications of the mylk1 gene protein products are reviewed, which altogether might determine the role and place of MLCK in physiological and pathological reactions of cells and entire organisms. Translational potential of MLCK as a drug target is evaluated.