PM2.5 Exposure of Mice during Spermatogenesis: A Role of Inhibitor κB Kinase 2 in Pro-Opiomelanocortin Neurons.

BACKGROUND: Epidemiological studies have shown that exposure to ambient fine particulate matter with aerodynamic diameter less than or equal to 2.5 µm (PM2.5) correlates with a decrease in sperm count, but the biological mechanism remains elusive. OBJECTIVES: This study tested whether hypothalamic inflammation, an emerging pathophysiological mediator, mediates the development of lower epididymal sperm count due to PM2.5 exposure. METHODS: Inhibitor κB kinase 2 (IKK2) was conditionally knocked out either in all neurons or subtypes of hypothalamic neurons of mice. Effects of concentrated ambient PM2.5 (CAP) exposure on hypothalamic inflammation, the hypothalamic-pituitary-gonadal (HPG) axis, and epididymal sperm count of these mouse models were then assessed. Furthermore, to test whether hypothalamic inflammation is sufficient to decrease sperm production, we overexpressed constitutively active IKK2 (IKK2ca) either in all neurons or subtypes of hypothalamic neurons and assessed hypothalamic inflammation, the HPG axis, and sperm production of these overexpression mouse models. RESULTS: CAP-exposed wild-type control mice vs. filtered air (FA)-exposed wild-type control mice had a higher expression of hypothalamic inflammatory markers, lower functional indexes of the HPG axis, and a lower epididymal sperm count. In contrast, all these measurements for CAP- vs. FA-exposed mice deficient of IKK2 in all neurons were comparable. We also found that overexpression of IKK2ca in either all neurons or pro-opiomelanocortin (POMC) neurons only, but not in Agouti-related protein (AgRP) neurons only, resulted in lower functional indexes of the HPG axis and a lower epididymal sperm count. Moreover, we showed that CAP- vs. FA-exposed mice deficient of IKK2 in POMC neurons had a comparable expression of hypothalamic inflammatory markers, comparable functional indexes of the HPG axis, and a comparable epididymal sperm count. DISCUSSION: This mouse model study shows a causal role of IKK2 of POMC neurons in the development of lower epididymal sperm count due to PM2.5 exposure, providing a mechanistic insight into this emerging pathogenesis. https://doi.org/10.1289/EHP8868.

Concentrated Ambient PM2.5-Induced Inflammation and Endothelial Dysfunction in a Murine Model of Neural IKK2 Deficiency.

BACKGROUND: Exposure to ambient fine particulate matter (PM2.5) is associated with cardiovascular mortality, but underlying pathophysiologic mechanisms are not fully understood. Hypothalamic inflammation, characterized by the activation of Inhibitor kappaB kinase 2/Nuclear factor kappaB (IKK2/NF-κB) signaling pathway, may play an important role in the pathogenesis of cardiovascular diseases. We recently demonstrated that hypothalamic inflammation is increased in mice exposed to concentrated ambient PM2.5 (CAP). OBJECTIVES: In the present study, we used a neuron-specific IKK2 knockout mouse model to examine the role of neural IKK2 expression and hypothalamic inflammation in the pathophysiologic effects of PM2.5. METHODS: We assessed inflammatory and vascular responses in Nestin-creIKK2flox/flox (IKK2Neu-KO) and littermate Nestin-creIKK2flox/+ (control) mice after 4 mo of exposure to filtered air (FA) or CAP. RESULTS: CAP exposure was associated with significantly higher tumor necrosis factor-α (TNFα) and interleukin (IL)-6 mRNA in the hypothalamus of control mice, but not IKK2Neu-KO mice. In addition, CAP exposure-induced increases in bronchoalveolar lavage fluid (BALF) leukocytes, pulmonary macrophage infiltration and IL-6 expression, plasma TNFα and IL-1ß levels, adipose macrophage infiltration and IL-1ß expression, and endothelial dysfunction were reduced or absent in IKK2Neu-KO mice compared with controls. CONCLUSIONS: Our findings support a role of neural IKK2 in CAP exposure-induced local and systemic pro-inflammatory cytokine expression, pulmonary and adipose inflammation, and endothelial dysfunction, thus providing insight into pathophysiologic mechanisms that may mediate effects of PM2.5 exposure. https://doi.org/10.1289/EHP2311.

Decreased Taurine and Creatine in the Thalamus May Relate to Behavioral Impairments in Ethanol-Fed Mice: A Pilot Study of Proton Magnetic Resonance Spectroscopy.

Minimal hepatic encephalopathy (MHE) is highly prevalent, observed in up to 80% of patients with liver dysfunction. Minimal hepatic encephalopathy is defined as hepatic encephalopathy with cognitive deficits and no grossly evident neurologic abnormalities. Clinical management may be delayed due to the lack of in vivo quantitative methods needed to reveal changes in brain neurobiochemical biomarkers. To gain insight into the development of alcoholic liver disease-induced neurological dysfunction (NDF), a mouse model of late-stage alcoholic liver fibrosis (LALF) was used to investigate changes in neurochemical levels in the thalamus and hippocampus that relate to behavioral changes. Proton magnetic resonance spectroscopy of the brain and behavioral testing were performed to determine neurochemical alterations and their relationships to behavioral changes in LALF. Glutamine levels were higher in both the thalamus and hippocampus of alcohol-treated mice than in controls. Thalamic levels of taurine and creatine were significantly diminished and strongly correlated with alcohol-induced behavioral changes. Chronic long-term alcohol consumption gives rise to advanced liver fibrosis, neurochemical changes in the nuclei, and behavioral changes which may be linked to NDF. Magnetic resonance spectroscopy represents a sensitive and noninvasive measurement of pathological alterations in the brain, which may provide insight into the pathogenesis underlying the development of MHE.

From the Cover: Lung-Specific Overexpression of Constitutively Active IKK2 Induces Pulmonary and Systemic Inflammations but Not Hypothalamic Inflammation and Glucose Intolerance.

The lung is constantly exposed to ambient pollutants such as ambient fine particulate matter (PM2.5), making it one of the most frequent locations of inflammation in the body. Given the establishment of crucial role of inflammation in the pathogenesis of cardiometabolic diseases, pulmonary inflammation is thus widely believed to be an important risk factor for cardiometabolic diseases. However, the causality between them has not yet been well established. To determine if pulmonary inflammation is sufficient to cause adverse cardiometabolic effects, SFTPC-rtTA+/-tetO-cre+/-pROSA-inhibitor κB kinase 2(IKK2)ca+/- (LungIKK2ca) and littermate SFTPC-rtTA+/-tetO-cre-/-pROSA-IKK2ca+/- wildtype (WT) mice were fed with doxycycline diet to induce constitutively active Ikk2 (Ikk2ca) overexpression in the lung and their pulmonary, systemic, adipose, and hypothalamic inflammations, vascular function, and glucose homeostasis were assessed. Feeding with doxycycline diet resulted in IKK2ca overexpression in the lungs of LungIKK2ca but not WT mice. This induction of IKK2ca was accompanied by marked pulmonary inflammation as evidenced by significant increases in bronchoalveolar lavage fluid leukocytes, pulmonary macrophage infiltration, and pulmonary mRNA expression of tumor necrosis factor α (Tnfα) and interleukin-6 (Il-6). This pulmonary inflammation due to lung-specific overexpression of IKK2ca was sufficient to increase circulating TNFα and IL-6 levels, adipose expression of Tnfα and Il-6 mRNA, aortic endothelial dysfunction, and systemic insulin resistance. Unexpectedly, no significant alteration in hypothalamic expression of Tnfα and Il-6 mRNA and glucose intolerance were observed in these mice. Pulmonary inflammation is sufficient to induce systemic inflammation, endothelial dysfunction, and insulin resistance, but not hypothalamic inflammation and glucose intolerance.

Programming of mouse obesity by maternal exposure to concentrated ambient fine particles.

BACKGROUND: Many diseases including obesity may originate through alterations in the early-life environment that interrupts fetal development. Increasing evidence has shown that exposure to ambient fine particles (PM2.5) is associated with abnormal fetal development. However, its long-term metabolic effects on offspring have not been systematically investigated. RESULTS: To determine if maternal exposure to PM2.5 programs offspring obesity, female C57Bl/6j mice were exposed to filtered air (FA) or concentrated ambient PM2.5 (CAP) during pre-conception, pregnancy, and lactation, and the developmental and metabolic responses of offspring were assessed. The growth trajectory of offspring revealed that maternal exposure to CAP significantly decreased offspring birth weight but increased body weight of adult male but not female offspring, and the latter was expressed as increased adiposity. These adult male offspring had increased food intake, but were sensitive to exogenous leptin. Their hypothalamic expression of Socs3 and Pomc, two target genes of leptin, was not changed, and the hypothalamic expression of NPY, an orexigenic peptide that is inhibited by leptin, was significantly increased. These decreases in central anorexigenic signaling were accompanied by reduced plasma leptin and its expression in adipose tissues, the primary source of circulating leptin. In contrast, maternal exposure did not significantly change any of these indexes in adult female offspring. Pyrosequencing demonstrated that the leptin promoter methylation of adipocytes was significantly increased in CAP-exposed male but not female offspring. CONCLUSIONS: Our data indicate that maternal exposure to ambient PM2.5 programs obesity in male offspring probably through alterations in the methylation of the promoter region of the leptin gene.

Exposure to concentrated ambient particulate matter induces reversible increase of heart weight in spontaneously hypertensive rats.

BACKGROUND: Exposure to ambient PM2.5 increases cardiovascular mortality and morbidity. To delineate the underlying biological mechanism, we investigated the time dependence of cardiovascular response to chronic exposure to concentrated ambient PM2.5 (CAP). METHODS: Spontaneously hypertensive rats (SHR) were exposed to CAP for 15 weeks, and blood pressure (BP), cardiac function and structure, and inflammations of lung, hypothalamus, and heart were measured at different time points. RESULTS: Chronic exposure to CAP significantly increased BP, and withdrawal from CAP exposure restored BP. Consistent with its BP effect, chronic exposure to CAP significantly decreased cardiac stroke volume and output in SHR, accompanied by increased heart weight and increased cardiac expression of hypertrophic markers ACTA1 and MYH7. Withdrawal from CAP exposure restored cardiac function, weight, and expression of hypertrophic markers, supporting the notion that cardiac dysfunction and hypertrophy is subsequent to hypertension. In agreement with the role of systemic inflammation in mediating the cardiovascular effects of CAP exposure, chronic exposure to CAP markedly increased expression of pro-inflammatory cytokines in lung, heart, and hypothalamus. However, withdrawal from exposure resolves inflammation in the heart and hypothalamus, but not in the lung, suggesting that CAP exposure-induced systemic inflammation may be independent of pulmonary inflammation. CONCLUSION: Chronic exposure to CAP induces reversible cardiac dysfunction and hypertrophy, which is likely to be subsequent to the elevation in BP and induction of systemic inflammation as evidenced by increased mRNA expression of pro-inflammatory cytokines in diverse tissues.

Central IKKß inhibition prevents air pollution mediated peripheral inflammation and exaggeration of type II diabetes.

BACKGROUND: Prior experimental and epidemiologic data support a link between exposure to fine ambient particulate matter (<2.5 µm in aerodynamic diameter, PM2.5) and development of insulin resistance/Type II diabetes mellitus (Type II DM). We investigated the role of hypothalamic inflammation in PM2.5-mediated diabetes development. METHODS: KKay mice, a genetically susceptible model of Type II DM, were assigned to either concentrated PM2.5 or filtered air (FA) for 4-8 weeks via a versatile aerosol concentrator and exposure system, or administered intra-cerebroventricular with either IKKß inhibitor (IMD-0354) or TNFα antibody (infliximab) for 4-5 weeks simultaneously with PM2.5 exposure. Glucose tolerance, insulin sensitivity, oxygen consumption and heat production were evaluated. At euthanasia, blood, spleen, visceral adipose tissue and hypothalamus were collected to measure inflammatory cells using flow cytometry. Standard immunohistochemical methods and quantitative PCR were used to assess targets of interest. RESULTS: PM2.5 exposure led to hyperglycemia and insulin resistance, which was accompanied by increased hypothalamic IL-6, TNFα, and IKKß mRNA expression and microglial/astrocyte reactivity. Targeting the NFκB pathway with intra-cerebroventricular administration of an IKKß inhibitor [IMD-0354, n = 8 for each group)], but not TNFα blockade with infliximab [(n = 6 for each group], improved glucose tolerance, insulin sensitivity, rectified energy homeostasis (O2 consumption, CO2 production, respiratory exchange ratio and heat generation) and reduced peripheral inflammation in response to PM2.5. CONCLUSIONS: Central inhibition of IKKß prevents PM2.5 mediated peripheral inflammation and exaggeration of type II diabetes. These results provide novel insights into how air pollution may mediate susceptibility to insulin resistance and Type II DM.

Long-term exposure to concentrated ambient PM2.5 increases mouse blood pressure through abnormal activation of the sympathetic nervous system: a role for hypothalamic inflammation.

BACKGROUND: Exposure to particulate matter≤2.5 µm in diameter (PM2.5) increases blood pressure (BP) in humans and animal models. Abnormal activation of the sympathetic nervous system may have a role in the acute BP response to PM2.5 exposure. The mechanisms responsible for sympathetic nervous system activation and its role in chronic sustenance of hypertension in response to PM2.5 exposure are currently unknown. OBJECTIVES: We investigated whether central nervous system inflammation may be implicated in chronic PM2.5 exposure-induced increases in BP and sympathetic nervous system activation. METHODS: C57BL/6J mice were exposed to concentrated ambient PM2.5 (CAPs) for 6 months, and we analyzed BP using radioactive telemetric transmitters. We assessed sympathetic tone by measuring low-frequency BP variability (LF-BPV) and urinary norepinephrine excretion. We also tested the effects of acute pharmacologic inhibitors of the sympathetic nervous system and parasympathetic nervous system. RESULTS: Long-term CAPs exposure significantly increased basal BP, paralleled by increases in LF-BPV and urinary norepinephrine excretion. The increased basal BP was attenuated by the centrally acting α2a agonist guanfacine, suggesting a role of increased sympathetic tone in CAPs exposure-induced hypertension. The increase in sympathetic tone was accompanied by an inflammatory response in the arcuate nucleus of the hypothalamus, evidenced by increased expression of pro-inflammatory genes and inhibitor kappaB kinase (IKK)/nuclear factor-kappaB (NF-κB) pathway activation. CONCLUSION: Long-term CAPs exposure increases BP through sympathetic nervous system activation, which may involve hypothalamic inflammation.

Lipoic acid effects on established atherosclerosis.

AIMS: Alpha-lipoic acid (LA) is a commonly used dietary supplement that exerts anti-oxidant and anti-inflammatory effects in vivo and in vitro. We investigated the mechanisms by which LA may confer protection in models of established atherosclerosis. MAIN METHODS: Watanabe heritable hyperlipidemic (WHHL) rabbits were fed with high cholesterol chow for 6 weeks and then randomized to receive either high cholesterol diet alone or combined with LA (20mg/kg/day) for 12 weeks. Vascular function was analyzed by myography. The effects of LA on T cell migration to chemokine gradients was assessed by Boyden chamber. NF-kappaB activation was determined by measuring translocation and electrophoresis migration shift assay (EMSA). KEY FINDINGS: LA decreased body weight by 15+/-5% without alterations in lipid parameters. Magnetic Resonance Imaging (MRI) analysis demonstrated that LA reduced atherosclerotic plaques in the abdominal aorta, with morphological analysis revealing reduced lipid and inflammatory cell content. Consistent with its effect on atherosclerosis, LA improved vascular reactivity (decreased constriction to angiotensin II and increased relaxation to acetylcholine and insulin), inhibited NF-kappaB activation, and decreased oxidative stress and expression of key adhesion molecules in the vasculature. LA reduced T cell content in atherosclerotic plaque in conjunction with decreasing ICAM and CD62L (l-selectin) expression. These effects were confirmed by demonstration of a direct effect of LA in reducing T cell migration in response to CCL5 and SDF-1 and decreasing T cell adhesion to the endothelium by intra-vital microscopy. SIGNIFICANCE: The present findings offer a mechanistic insight into the therapeutic effects of LA on atherosclerosis.