BackgroundElevated levels of ceramide, a sphingolipid known to cause a transition from nitric oxide (NO)– to hydrogen peroxide–dependent flow‐induced dilation (FID) in human arterioles, correlate with adverse cardiac events. However, elevations of ceramide are associated with changed concentrations of other sphingolipid metabolites. The effects of sphingolipid metabolites generated through manipulation of this lipid pathway on microvascular function are unknown. We examined the hypothesis that inhibition or activation of the ceramide pathway would determine the mediator of FID.Methods and ResultsUsing videomicroscopy, internal diameter changes were measured in human arterioles collected from discarded adipose tissue during surgery. Inhibition of neutral ceramidase, an enzyme responsible for the hydrolysis of ceramide, favored hydrogen peroxide–dependent FID in arterioles from healthy patients. Using adenoviral technology, overexpression of neutral ceramidase in microvessels from diseased patients resulted in restoration of NO‐dependent FID. Exogenous sphingosine‐1‐phosphate, a sphingolipid with opposing effects of ceramide, also restored NO as the mediator of FID in diseased arterioles. Likewise, exogenous adiponectin, a known activator of neutral ceramidase, or, activation of adiponectin receptors, favored NO‐dependent dilation in arterioles collected from patients with coronary artery disease.ConclusionsSphingolipid metabolites play a critical role in determining the mediator of FID in human resistance arterioles. Manipulating the sphingolipid balance towards ceramide versus sphingosine‐1‐phosphate favors microvascular dysfunction versus restoration of NO‐mediated FID, respectively. Multiple targets exist within this biolipid pathway to treat microvascular dysfunction and potentially improve patient outcomes.

Background: ESCRT-III can enhance Vta1 stimulation of Vps4 ATPase activity via the Vps4 stimulatory element (VSE) of Vta1. Results: ␣7 and ␣9 of the Vps4 small AAA domain mediate VSE stimulation, contributing to Vps4 function in vivo. Conclusion: Vta1 contacts Vps4 ␣7 and ␣9 during ESCRT-III-enhanced stimulation of Vps4. Significance: These studies identify a novel mechanism of Vps4 stimulation.

The membrane deforming dynamin family members MxA and MxB are large GTPases that convey resistance to a variety of infectious viruses. During viral infection, Mx proteins are known to show markedly increased expression via an interferon-responsive promoter to associate with nuclear pores. In this study we report that MxB is an inner mitochondrial membrane GTPase that plays an important role in the morphology and function of this organelle. Expression of mutant MxB or siRNA knockdown of MxB leads to fragmented mitochondria with disrupted inner membranes that are unable to maintain a proton gradient, while expelling their nucleoid-based genome into the cytoplasm. These findings implicate a dynamin family member in mitochondrial-based changes frequently observed during an interferon-based, anti-viral response.

Background: Preclinical studies suggest that S1P (sphingosine-1-phosphate) influences blood pressure regulation primarily through NO-induced vasodilation. Because microvascular tone significantly contributes to mean arterial pressure, the mechanism of S1P on human resistance arterioles was investigated. We hypothesized that S1P induces NO-mediated vasodilation in human arterioles from adults without coronary artery disease (non–coronary artery disease) through activation of 2 receptors, S1PR 1 (S1P receptor 1) and S1PR 3 (S1P receptor 3). Furthermore, we tested whether this mechanism is altered in vessels from patients diagnosed with coronary artery disease. methods: Human arterioles (50–200 µm in luminal diameter) were dissected from otherwise discarded surgical adipose tissue, cannulated, and pressurized. Following equilibration, resistance vessels were preconstricted with ET-1 (endothelin-1) and changes in internal diameter to increasing concentrations of S1P (10-12 to 10-7 M) in the presence or absence of various inhibitors were measured. Results: S1P resulted in significant dilation that was abolished in vessels treated with S1PR 1 and S1PR 3 inhibitors and in vessels with reduced expression of each receptor. Dilation to S1P was significantly reduced in the presence of the NOS (NO synthase) inhibitor Nω-nitro-L-arginine methyl ester and the NO scavenger 2-4-(carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. Interestingly, dilation was also significantly impaired in the presence of PEG-catalase (polyethylene glycol–catalase), apocynin, and specific inhibitors of NOX (NADPH oxidases) 2 and 4. Dilation in vessels from patients diagnosed with coronary artery disease was dependent on H 2 O 2 alone which was only dependent on S1PR 3 activation. Conclusions: These translational studies highlight the inter-species variation observed in vascular signaling and provide insight into the mechanism by which S1P regulates microvascular resistance and ultimately blood pressure in humans.