Ning Hua

Genetic disruption of myostatin reduces the development of proatherogenic dyslipidemia and atherogenic lesions in Ldlr null mice

OBJECTIVE Insulin-resistant states, such as obesity and type 2 diabetes, contribute substantially to accelerated atherogenesis. Null mutations of myostatin (Mstn) are associated with increased muscle mass and decreased fat mass. In this study, we determined whether Mstn disruption could prevent the development of insulin resistance, proatherogenic dyslipidemia, and atherogenesis. RESEARCH DESIGN AND METHODS C57BL/6 Ldlr−/− mice were cross-bred with C57BL/6 Mstn−/− mice for >10 generations to generate Mstn−/−/Ldlr−/− double-knockout mice. The effects of high-fat/high-cholesterol diet on body composition, plasma lipids, systemic and tissue-specific insulin sensitivity, hepatic steatosis, as well as aortic atheromatous lesion were characterized in Mstn−/−/Ldlr−/− mice in comparison with control Mstn+/+/Ldlr−/− mice. RESULTS Compared with Mstn+/+/Ldlr−/− controls, Mstn−/−/ Ldlr−/− mice were resistant to diet-induced obesity, and had greatly improved insulin sensitivity, as indicated by 42% higher glucose infusion rate and 90% greater muscle [3H]-2-deoxyglucose uptake during hyperinsulinemic-euglycemic clamp. Mstn−/−/Ldlr−/− mice were protected against diet-induced hepatic steatosis and had 56% higher rate of hepatic fatty acid β-oxidation than controls. Mstn−/−/Ldlr−/− mice also had 36% lower VLDL secretion rate and were protected against diet-induced dyslipidemia, as indicated by 30–60% lower VLDL and LDL cholesterol, free fatty acids, and triglycerides. Magnetic resonance angiography and en face analyses demonstrated 41% reduction in aortic atheromatous lesions in Ldlr−/− mice with Mstn deletion. CONCLUSIONS Inactivation of Mstn protects against the development of insulin resistance, proatherogenic dyslipidemia, and aortic atherogenesis in Ldlr−/− mice. Myostatin may be a useful target for drug development for prevention and treatment of obesity and its associated type 2 diabetes and atherosclerosis.

Porphyromonas gingivalis Accelerates Inflammatory Atherosclerosis in the Innominate Artery of ApoE Deficient Mice

OBJECTIVE Studies in humans support a role for the oral pathogen Porphyromonas gingivalis in the development of inflammatory atherosclerosis. The goal of this study was to determine if P. gingivalis infection accelerates inflammation and atherosclerosis in the innominate artery of mice, an artery which has been reported to exhibit many features of human atherosclerotic disease, including plaque rupture. METHODS AND RESULTS Apolipoprotein E-deficient (ApoE-/-) mice were orally infected with P. gingivalis, and magnetic resonance imaging (MRI) was used to monitor the progression of atherosclerosis in live mice. P. gingivalis infected mice exhibited a statistically significant increase in atherosclerotic plaque in the innominate artery as compared to uninfected mice. Polarized light microscopy and immunohistochemistry revealed that the innominate arteries of infected mice had increased lipids, macrophages and T cells as compared to uninfected mice. Increases in plaque, total cholesterol esters and cholesterol monohydrate crystals, macrophages, and T cells were prevented by immunization with heat-killed P. gingivalis prior to pathogen exposure. CONCLUSIONS These are the first studies to demonstrate progression of inflammatory plaque accumulation in the innominate arteries by in vivo MRI analysis following pathogen exposure, and to document protection from plaque progression in the innominate artery via immunization.

In vivo detection of vulnerable atherosclerotic plaque by MRI in a rabbit model

Background—The ability to identify atherosclerotic plaques with a high risk for sudden disruption before stroke or myocardial infarction would be of great utility. We used a rabbit model of controlled atherothrombosis to test whether in vivo MRI can noninvasively distinguish between plaques that disrupt after pharmacological triggering (vulnerable) and those that do not (stable). Methods and Results—Atherosclerosis was induced in male New Zealand White (n=17) rabbits by cholesterol diet and endothelial denudation of the abdominal aorta. After baseline (pretrigger) MRI with and without gadolinium contrast, the rabbits underwent 2 pharmacological triggerings to induce atherothrombosis, followed by another MRI 48 hours later (post-triggering). Atherosclerosis was identified by the pretriggered images in all rabbits, and thrombosis was identified in 9 of 17 animals (53%) by post-trigger MRI. After the animals were euthanized, 95 plaques were analyzed; 28 (29.5%) had thrombi (vulnerable) and 67 did not (stable) (70.5%). Pretriggered MRI revealed comparable stenosis in stable and vulnerable plaques, but vulnerable plaques had a larger plaque area (4.8±1.6 versus 3.0±1.0 mm2; P=0.01), vessel area (9.2±3.0 versus. 15.8±4.9 mm2; P=0.01), and higher remodeling ratio (1.16±0.2 versus 0.93±0.2; P=0.01) compared with stable plaques. Furthermore, vulnerable plaques more frequently exhibited (1) positive remodeling (67.8% versus 22.3%; P=0.01), in which the plaque is hidden within the vessel wall instead of occluding the lumen; and (2) enhanced gadolinium uptake (78.6% versus 20.9%; P=0.01) associated with histological findings of neovascularization, inflammation, and tissue necrosis. Conclusions—We demonstrate that in vivo MRI at 3.0 T detects features of vulnerable plaques in an animal model of controlled atherothrombosis. These findings suggest that MRI may be used as a noninvasive modality for localization of plaques that are prone to disruption.

In vivo Detection of Vulnerable Atherosclerotic Plaque by Magnetic Resonance Imaging in a Rabbit Model

Background—The ability to identify atherosclerotic plaques with a high risk for sudden disruption before stroke or myocardial infarction would be of great utility. We used a rabbit model of controlled atherothrombosis to test whether in vivo MRI can noninvasively distinguish between plaques that disrupt after pharmacological triggering (vulnerable) and those that do not (stable). Methods and Results—Atherosclerosis was induced in male New Zealand White (n=17) rabbits by cholesterol diet and endothelial denudation of the abdominal aorta. After baseline (pretrigger) MRI with and without gadolinium contrast, the rabbits underwent 2 pharmacological triggerings to induce atherothrombosis, followed by another MRI 48 hours later (post-triggering). Atherosclerosis was identified by the pretriggered images in all rabbits, and thrombosis was identified in 9 of 17 animals (53%) by post-trigger MRI. After the animals were euthanized, 95 plaques were analyzed; 28 (29.5%) had thrombi (vulnerable) and 67 did not (stable) (70.5%). Pretriggered MRI revealed comparable stenosis in stable and vulnerable plaques, but vulnerable plaques had a larger plaque area (4.8±1.6 versus 3.0±1.0 mm2; P=0.01), vessel area (9.2±3.0 versus. 15.8±4.9 mm2; P=0.01), and higher remodeling ratio (1.16±0.2 versus 0.93±0.2; P=0.01) compared with stable plaques. Furthermore, vulnerable plaques more frequently exhibited (1) positive remodeling (67.8% versus 22.3%; P=0.01), in which the plaque is hidden within the vessel wall instead of occluding the lumen; and (2) enhanced gadolinium uptake (78.6% versus 20.9%; P=0.01) associated with histological findings of neovascularization, inflammation, and tissue necrosis. Conclusions—We demonstrate that in vivo MRI at 3.0 T detects features of vulnerable plaques in an animal model of controlled atherothrombosis. These findings suggest that MRI may be used as a noninvasive modality for localization of plaques that are prone to disruption.

Distinct Lipid A Moieties Contribute to Pathogen-Induced Site-Specific Vascular Inflammation

Several successful pathogens have evolved mechanisms to evade host defense, resulting in the establishment of persistent and chronic infections. One such pathogen, Porphyromonas gingivalis, induces chronic low-grade inflammation associated with local inflammatory bone loss and systemic inflammation manifested as atherosclerosis. P. gingivalis expresses an atypical lipopolysaccharide (LPS) structure containing heterogeneous lipid A species, that exhibit Toll-like receptor-4 (TLR4) agonist or antagonist activity, or are non-activating at TLR4. In this study, we utilized a series of P. gingivalis lipid A mutants to demonstrate that antagonistic lipid A structures enable the pathogen to evade TLR4-mediated bactericidal activity in macrophages resulting in systemic inflammation. Production of antagonistic lipid A was associated with the induction of low levels of TLR4-dependent proinflammatory mediators, failed activation of the inflammasome and increased bacterial survival in macrophages. Oral infection of ApoE−/− mice with the P. gingivalis strain expressing antagonistic lipid A resulted in vascular inflammation, macrophage accumulation and atherosclerosis progression. In contrast, a P. gingivalis strain producing exclusively agonistic lipid A augmented levels of proinflammatory mediators and activated the inflammasome in a caspase-11-dependent manner, resulting in host cell lysis and decreased bacterial survival. ApoE−/− mice infected with this strain exhibited diminished vascular inflammation, macrophage accumulation, and atherosclerosis progression. Notably, the ability of P. gingivalis to induce local inflammatory bone loss was independent of lipid A expression, indicative of distinct mechanisms for induction of local versus systemic inflammation by this pathogen. Collectively, our results point to a pivotal role for activation of the non-canonical inflammasome in P. gingivalis infection and demonstrate that P. gingivalis evades immune detection at TLR4 facilitating chronic inflammation in the vasculature. These studies support the emerging concept that pathogen-mediated chronic inflammatory disorders result from specific pathogen-mediated evasion strategies resulting in low-grade chronic inflammation.

Key research issues concerning the conservation of migratory shorebirds in the Yellow Sea region

The widespread decline of migratory shorebirds in the East Asian-Australasian Flyway (EAAF) is one of the greatest crises for migrating birds. Among the migratory species with known population trends, 88% (22 of 25 species) show population declines, and seven have been listed as threatened or Near Threatened in the IUCN Red List. The decline of migratory shorebirds is related to the deterioration of stopping sites (including staging and stopping sites) in the Yellow Sea, including loss of intertidal wetlands, spread of invasive smooth cordgrass Spartina alterniflora on intertidal flats, an increase in pollution, and an increase in human disturbance. We review research concerning shorebird migration through the Yellow Sea and highlight key research activities required for the conservation of shorebirds in the region. These activities include: confirming the population consequences of loss of stopping sites, estimating migration timing and numbers of shorebirds at stopping sites, determining the differing abilities of species to use alternative habitats, understanding intra- and interspecific differences in the use of stopping sites, maintaining and expanding surveys on shorebirds and habitat condition, and identifying threats to shorebirds beyond habitat loss by reclamation. The information generated by these research activities is required for the design and selection of effective conservation actions to reverse the decline in shorebird populations.

Regions of Low Endothelial Shear Stress Colocalize With Positive Vascular Remodeling and Atherosclerotic Plaque Disruption An In Vivo Magnetic Resonance Imaging Study

Background— Local hemodynamic factors, particularly low endothelial shear stress (ESS), play a role in the focal formation of atherosclerosis. We used in vivo MRI to investigate the role of the magnitude of ESS on vascular remodeling, plaque burden, and disruption using a rabbit model of controlled atherothrombosis. Methods and Results— Atherosclerosis was induced in New Zealand white rabbits by cholesterol diet and endothelial denudation. MRI was performed before (pretrigger) and after (posttrigger) inducing plaque disruption with Russell viper venom and histamine. Of the 134 vascular segments studied, 28 contained thrombus (disrupted) and 106 did not (nondisrupted). Disrupted plaques were histologically characterized by a thin, inflamed fibrous cap, a dense lipid core, and mural thrombus. Pretriggered MRI revealed that disrupted plaques clustered at regions with low mean ESS (11.55±5.3 versus 20.9±9.74 dynes/cm2; P<0.001) and low peak ESS (21.5±11.2 versus 49.2±21.5 dynes/cm2; P<0.001) compared with nondisrupted plaques. The peak ESS negatively correlated with the plaque area (r=−0.56, P<0.001) and remodeling ratio (r=−0.4, P=0.008). There was also a negative correlation between the mean ESS and the remodeling ratio (r=−0.55, P<0.001). Both the peak ESS and the mean ESS did not correlate with the % stenosis; there was a weak but statistically significant correlation with the % cross-sectional narrowing (r=0.3, P=0.002 and r=0.2, P=0.04, respectively). Receiver operating characteristic analysis showed that both mean (Area under the curve=0.78; 95% CI, 0.69–0.87) and peak ESS (Area under the curve=0.85; 95% CI, 0.78–0.93) identified disrupted plaques. Conclusions— We demonstrated that low ESS is associated with plaque burden, positive vascular remodeling, and plaque disruption in a rabbit model. Assessment of ESS by noninvasive MRI might be useful for assessing atherosclerotic risk.

The Relationship of Ectopic Lipid Accumulation to Cardiac and Vascular Function in Obesity and Metabolic Syndrome

Storage of lipid in ectopic depots outside of abdominal visceral and subcutaneous stores, including within the pericardium and liver, has been associated with obesity, insulin resistance, and cardiovascular risk. We sought to determine whether anatomically distinct ectopic depots were physiologically correlated and site‐specific effects upon cardiovascular function could be identified. Obese subjects (n = 28) with metabolic syndrome but without known atherosclerotic disease and healthy controls (n = 18) underwent magnetic resonance imaging (MRI) and proton MR spectroscopy (MRS) to quantify pericardial and periaortic lipid volumes, cardiac function, aortic compliance, and intrahepatic lipid content. Fasting plasma lipoproteins, glucose, insulin, and free‐fatty acids were measured. Pericardial and intrahepatic (P < 0.01) and periaortic (P < 0.05) lipid volumes were increased in obese subjects vs. controls and were strongly and positively correlated (P ≤ 0.01) but independent of BMI (P = NS) among obese subjects. Intrahepatic lipid was associated with insulin resistance (P < 0.01) and triglycerides (P < 0.05), whereas pericardial and periaortic lipid were not (P = NS). Periaortic and pericardial lipid positively correlated to free‐fatty acids (P ≤ 0.01) and negatively correlated to high‐density lipoprotein (HDL) cholesterol (P < 0.05). Pericardial lipid negatively correlated to cardiac output (P = 0.03) and stroke volume (P = 0.01) but not to left ventricular ejection fraction (P = 0.46). None of the ectopic depots correlated to aortic compliance. In conclusion, ectopic storage of lipid in anatomically distinct depots appeared tightly correlated but independent of body size. Site‐specific functional abnormalities were observed for pericardial but not periaortic lipid. These findings underscore the utility of MRI to assess individual differences in ectopic lipid that are not predictable from BMI.

Concussion, microvascular injury, and early tauopathy in young athletes after impact head injury and an impact concussion mouse model

The mechanisms underpinning concussion, traumatic brain injury (TBI) and chronic traumatic encephalopathy (CTE) are poorly understood. Using neuropathological analyses of brains from teenage athletes, a new mouse model of concussive impact injury, and computational simulations, Tagge et al. show that head injuries can induce TBI and early CTE pathologies independent of concussion.

Economic design in a long-distance migrating molluscivore: how fast-fuelling red knots in Bohai Bay, China, get away with small gizzards

SUMMARY We carried out an observational and experimental study to decipher how resource characteristics, in interaction with the predators phenotype, constrain a fitness-determining performance measure, i.e. refuelling in a migrant bird. Two subspecies of red knot (Calidris canutus rogersi and C. c. piersmai) use northern Bohai Bay, Yellow Sea, China, for the final prebreeding stopover, during their 10,000–15,000 km long migrations between wintering and breeding areas. Here, they feed on small bivalves, especially 2–7 mm long Potamocorbula laevis. With an average stay of 29 days, and the need to store 80 g of fat for the onward flights to high-Arctic breeding grounds, red knots need to refuel fast. Using existing knowledge, we expected them to achieve this on the basis of (1) prey with high flesh to shell mass ratios, (2) large gizzards to crush the ingested molluscs, or (3) a combination of the two. Rejecting all three predictions, we found that red knots staging in Bohai Bay had the smallest gizzards on record (4.9±0.8 g, mean ± s.e.m., N=27), and also found that prey quality of P. laevis is much lower than predicted for the measured gizzard size (i.e. 1.3 rather than the predicted 4.5 kJ g−1 dry shell mass, DMshell). The estimated handling time of P. laevis (0.2 s) is much shorter than the observed time between two prey ingestions (0.7 s), indicating that prey handling time is no constraint. Based on field observations of dropping rates and on indoor digestion trails, the shell processing rate was estimated at 3.9 mg DMshell s−1, i.e. three times higher the rate previously predicted for red knots eating as fast as they can with the measured gizzard size. This is explained by the small and easily crushed P. laevis enabling high processing rates. As P. laevis also occurred in high densities, the metabolizable energy intake rate of red knots with small gizzards at 5 J s−1 was as high as at northward staging sites elsewhere in the world. Currently, therefore, food characteristics in Bohai Bay are such that red knots can refuel fast whilst economizing on the size of their gizzard. These time-stressed migrants thus provide an elegant example of symmorphosis.