MEF2B-Nox1 signaling is critical for stretch-induced phenotypic modulation of vascular smooth muscle cells.

OBJECTIVE: Blood vessel hemodynamics have profound influences on function and structure of vascular cells. One of the main mechanical forces influencing vascular smooth muscle cells (VSMC) is cyclic stretch (CS). Increased CS stimulates reactive oxygen species (ROS) production in VSMC, leading to their dedifferentiation, yet the mechanisms involved are poorly understood. This study was designed to test the hypothesis that pathological CS stimulates NADPH oxidase isoform 1 (Nox1)-derived ROS via MEF2B, leading to VSMC dysfunction via a switch from a contractile to a synthetic phenotype. APPROACH AND RESULTS: Using a newly developed isoform-specific Nox1 inhibitor and gene silencing technology, we demonstrate that a novel pathway, including MEF2B-Nox1-ROS, is upregulated under pathological stretch conditions, and this pathway promotes a VSMC phenotypic switch from a contractile to a synthetic phenotype. We observed that CS (10% at 1 Hz) mimicking systemic hypertension in humans increased Nox1 mRNA, protein levels, and enzymatic activity in a time-dependent manner, and this upregulation was mediated by MEF2B. Furthermore, we show that stretch-induced Nox1-derived ROS upregulated a specific marker for synthetic phenotype (osteopontin), whereas it downregulated classical markers for contractile phenotype (calponin1 and smoothelin B). In addition, our data demonstrated that stretch-induced Nox1 activation decreases actin fiber density and augments matrix metalloproteinase 9 activity, VSMC migration, and vectorial alignment. CONCLUSIONS: These results suggest that CS initiates a signal through MEF2B that potentiates Nox1-mediated ROS production and causes VSMC to switch to a synthetic phenotype. The data also characterize a new Nox1 inhibitor as a potential therapy for treatment of vascular dysfunction in hypertension.

Cyclic stretch induced IL-33 production through HMGB1/TLR-4 signaling pathway in murine respiratory epithelial cells.

Interleukin 33 (IL-33), an inflammatory and mechanically responsive cytokine, is an important component of a TLR4-dependent innate immune process in mucosal epithelium. Although TLR4 also plays a role in sensing biomechanical stretch, a pathway of stretch-induced TLR4-dependent IL-33 biosynthesis has not been revealed. In the current study, we show that short term (6 h) cyclic stretch (CS) of cultured murine respiratory epithelial cells (MLE-12) increased intracellular IL-33 expression in a TLR4 dependent fashion. There was no detectable IL-33 in conditioned media in this interval. CS, however, increased release of the notable alarmin, HMGB1, and a neutralizing antibody (2G7) to HMGB1 completely abolished the CS mediated increase in IL-33. rHMGB1 increased IL-33 synthesis and this was partially abrogated by silencing TLR4 suggesting additional receptors for HMGB1 are involved in its regulation of IL-33. Collectively, these data reveal a HMGB1/TLR4/IL-33 pathway in the response of respiratory epithelium to mechanical stretch.

Design and Validation of a Vacuum Assisted Anchorage for the Uniaxial Tensile Testing of Soft Materials.

Current commercial tensile testing systems use spring-loaded or other compression-based grips to clamp materials in place posing a problem for very soft or delicate materials that cannot withstand this mechanical clamping force. In order to perform uniaxial tensile tests on soft tissues or materials, we have created a novel vacuum-assisted anchor (VAA). Fibrin gels were subjected to uniaxial extension, and the testing data was used to determine material mechanical properties. Utilizing the VAA, we achieved successful tensile breaks of soft fibrin gels while finding statistically significant differences between the mechanical properties of gels fabricated at two different fibrinogen concentrations.

Periadventitial adipose-derived stem cell treatment halts elastase-induced abdominal aortic aneurysm progression.

AIM: Demonstrate that periadventitial delivery of adipose-derived mesenchymal stem cells (ADMSCs) slows aneurysm progression in an established murine elastase-perfusion model of abdominal aortic aneurysm (AAA). MATERIALS & METHODS: AAAs were induced in C57BL/6 mice using porcine elastase. During elastase perfusion, a delivery device consisting of a subcutaneous port, tubing and porous scaffold was implanted. Five days after elastase perfusion, 100,000 ADMSCs were delivered through the port to the aorta. After sacrifice at day 14, analyzed metrics included aortic diameter and structure of aortic elastin. RESULTS: ADMSC treated aneurysms had a smaller diameter and less fragmented elastin versus saline controls. CONCLUSION: Periadventitial stem cell delivery prevented the expansion of an established aneurysm between days 5 and 14 after elastase perfusion.