Acetylcholine synthesis, storage, degredation and nicotinic receptores in a rat model for space-induced muscle atrophy

Space flight results in loss of mass and function in skeletal muscle. Data from manned flights and animal biosatellites give evidence of possible changes in neuromuscular interactions. Components at the neuromuscular junction are a potential site of action for this space-induced muscle atrophy. We examined the nicotinic acetylcholine receptor population (Bmax) and affinity (Kd), the activity of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), and the endogenous levels of acetylcholine (ACh) and choline (Ch). We assayed the hindlimb soleus, gastrocnemius and tibialis, and the forelimb triceps brachii muscles after 1, 3 or 8 weeks of supsension. Bmax was greater than controls in the triceps brachii and in the gastrocnemius after 3 and 8 weeks of suspension respectively. Receptor Kd was decreased in the soleus muscles of rats suspended for 3 weeks. Enzyme activity decreased from control animals' levels in all 4 muscles, with the time to effect varying depending on the muscle and the enzyme. No difference was found in endogenous ACh levels in the soleus, but levels were increased in the gastrocnemius (3 weeks), and decreased in the tibialis (3 weeks) and triceps brachii (1 week). Ch levels were decreased in the soleus (1 and 3 weeks) and gastrocnemius (3 weeks) with no change from control levels in the tibialis and triceps brachii. Testosterone, as an anabolic hormone to skeletal muscle, was assayed in suspended and control rats. We found no difference from control animals in total testes tissue levels. Plasma levels were increased in suspended animals after 8 weeks

Age-Dependent Variability in Gene Expression in Male Fischer 344 Rat Retina

Recent evidence suggests that older adults may be a sensitive population with regard to environmental exposure to toxic compounds. One source of this sensitivity could be an enhanced variability in response. Studies on phenotypic differences have suggested that variation in response does increase with age. However, few reports address the question of variation in gene expression as an underlying cause for increased variability of phenotypic response in the aged. In this study, we utilized global analysis to compare variation in constitutive gene expression in the retinae of young (4 months), middle-aged (11 months), and aged (23 months) Fischer 344 rats. Three hundred and forty transcripts were identified in which variance in expression increased from 4 to 23 months of age, while only 12 transcripts were found for which it decreased. Functional roles for identified genes were clustered in basic biological categories including cell communication, function, metabolism, and response to stimuli. Our data suggest that population stochastically induced variability should be considered in assessing sensitivity due to old age

Atypical microglial response to biodiesel exhaust in healthy and hypertensive rats

Accumulating evidence suggests a deleterious role for urban air pollution in central nervous system (CNS) diseases and neurodevelopmental disorders. Microglia, the resident innate immune cells and sentinels in the brain, are a common source of neuroinflammation and are implicated in how air pollution may exert CNS effects. While renewable energy, such as soy-based biofuel, is of increasing public interest, there is little information on how soy biofuel may affect the brain. To address this, male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats were exposed to 100% Soy Biodiesel Exhaust (100SBDE; 0, 50, 150 and 500 μg/m3) by inhalation for 4 h/day for 4 weeks (5 days/week). IBA-1 staining of microglia in the substantia nigra revealed significant changes in morphology with 100SBDE exposure in rats from both genotypes, where the SHR were less sensitive. Further analysis failed to show consistent changes in pro-inflammatory cytokine expression, nitrated protein, and arginase1 expression in brain tissue from either rat strain exposed to 100SBDE. CX3CR1 and fractalkine mRNA expression were lower in the striatum of all 100SBDE exposed rats, but greater SBDE exposure was required for loss of fractalkine expression in the SHR. Together, these data support that month-long 100SBDE exposure impacts the basal ganglia with changes in microglia morphology, an impaired fractalkine axis, and an atypical activation response without traditional markers of M1 or M2 activation, where the SHR may be less sensitive to these effects

Developmental Exposure to a Commercial PBDE Mixture: Effects on Protein Networks in the Cerebellum and Hippocampus of Rats

Background: Polybrominated diphenyl ethers (PBDEs) are structurally similar to polychlorinated biphenyls (PCBs) and have both central (learning and memory deficits) and peripheral (motor dysfunction) neurotoxic effects at concentrations/doses similar to those of PCBs. The cellular and molecular mechanisms for these neurotoxic effects are not fully understood; however, several studies have shown that PBDEs affect thyroid hormones, cause oxidative stress, and disrupt Ca2+-mediated signal transduction. Changes in these signal transduction pathways can lead to differential gene regulation with subsequent changes in protein expression, which can affect the development and function of the nervous system

Diesel exhaust impairs TREM2 to dysregulate neuroinflammation

BACKGROUND: Air pollution has been linked to neurodegenerative diseases, including Alzheimer's disease (AD), and the underlying neuroimmune mechanisms remain poorly understood. TREM2 is a myeloid cell membrane receptor that is a key regulator of disease-associated microglia (DAM) cells, where loss-of-function TREM2 mutations are associated with an increased risk of AD. At present, the basic function of TREM2 in neuroinflammation is a point of controversy. Further, the impact of air pollution on TREM2 and the DAM phenotype is largely unknown. Using diesel exhaust (DE) as a model of urban air pollution exposure, we sought to address its impact on TREM2 expression, the DAM phenotype, the association of microglia with the neurovasculature, and the role of TREM2 in DE-induced neuroinflammation. METHODS: WYK rats were exposed for 4 weeks to DE (0, 50, 150, 500 μg/m3) by inhalation. DE particles (DEP) were administered intratracheally once (600 μg/mouse) or 8 times (100 μg/mouse) across 28 days to male mice (Trem2+/+, Trem2-/-, PHOX+/+, and PHOX-/-). RESULTS: Rats exposed to DE exhibited inverted-U patterns of Trem2 mRNA expression in the hippocampus and frontal cortex, while TREM2 protein was globally diminished, indicating impaired TREM2 expression. Analysis of DAM markers Cx3Cr1, Lyz2, and Lpl in the frontal cortex and hippocampus showed inverted-U patterns of expression as well, supporting dysregulation of the DAM phenotype. Further, microglial-vessel association decreased with DE inhalation in a dose-dependent manner. Mechanistically, intratracheal administration of DEP increased Tnf (TNFα), Ncf1 (p47PHOX), and Ncf2 (p67PHOX) mRNA expression in only Trem2+/+ mice, where Il1b (IL-1β) expression was elevated in only Trem2-/- mice, emphasizing an important role for TREM2 in DEP-induced neuroinflammation. CONCLUSIONS: Collectively, these findings reveal a novel role for TREM2 in how air pollution regulates neuroinflammation and provides much needed insight into the potential mechanisms linking urban air pollution to AD

Age- and Organ-Specific Differences in Mitochondrial Bioenergetics in Brown Norway Rats

Mitochondria play a central role in energy homeostasis and act as regulatory checkpoints for downstream metabolic responses and cell senescence processes during an entire life span. Acute or chronic environmental toxicant exposures have shown deleterious organ-specific human health issues at various life stages. Since mitochondria are a prime target for ensuing cellular bioenergetics responses and senescence, it is essential to understand mitochondrial bioenergetic responses in different organs over multiple life stages. Therefore, in the present study, we evaluated mitochondrial bioenergetic parameters in the liver, lung, and heart in four diverse age groups (young: 1 month; adult: 4 months; middle-aged: 12 months; old-aged: 24 month) using male Brown Norway rats as a model of aging (n = 5 sample size/organ/age group) and compared them with our previously published results on brain. Real-time mitochondrial bioenergetic parameters (i.e., State III, State IV, and State V) were measured using the Seahorse Extracellular Flux Analyzer. Additionally, mitochondrial enzyme pyruvate dehydrogenase complex (PDHC), Complex I, Complex II, and Complex IV activities were measured using Synergy HT plate reader. Our results indicated that nearly in all parameters, significant age- and organ-specific interactions were observed. We observed age-specific declines in State III (i.e., ATP synthesis rate) responses in both the heart and lung, where opposite was observed in the liver as age advances. Across the age, the heart has highest enzyme activities than the liver and lung. Interestingly, heart and liver mitochondrial bioenergetic rates and enzyme activities remain higher than the lung, which specifies their higher metabolic capabilities than the lung. Amongst all, bioenergetic rates and enzyme activities in the lung remain lowest suggesting the lung may display higher vulnerability and lower resilience to environmental toxicants during aging than other organs tested here. Overall, these age- and organ-specific findings may facilitate a more contextualized understanding of mitochondrial bioenergetic outcomes when considering the interactions of age-related sensitivities with exposure to chemical stressors from the environment

Interaction of Diet and Ozone Exposure on Oxidative Stress Parameters within Specific Brain Regions of Male Brown Norway Rats

Oxidative stress (OS) contributes to the neurological and cardio/pulmonary effects caused by adverse metabolic states and air pollutants such as ozone (O3). This study explores the interactive effects of O3 and diet (high-fructose (FRUC) or high⁻fat (FAT)) on OS in different rat brain regions. In acute exposure, there was a decrease in markers of reactive oxygen species (ROS) production in some brain regions by diet and not by O3. Total antioxidant substances (TAS) were increased in the cerebellum (CER) and frontal cortex (FC) and decreased in the striatum (STR) by both diets irrespective of O3 exposure. Protein carbonyls (PC) and total aconitase decreased in some brain regions irrespective of exposure. Following subacute exposure, an increase in markers of ROS was observed in both diet groups. TAS was increased in the FC (FAT only) and there was a clear O3 effect where TAS was increased in the FC and STR. Diet increased PC formation within the CER in the FAT group, while the hippocampus showed a decrease in PC after O3 exposure in controls. In general, these results indicate that diet/O3 did not have a global effect on brain OS parameters, but showed some brain region- and OS parameter-specific effects by diets

Developmental Exposure to a Commercial PBDE Mixture: Effects on Protein Networks in the Cerebellum and Hippocampus of Rats

Background: Polybrominated diphenyl ethers (PBDEs) are structurally similar to polychlorinated biphenyls (PCBs) and have both central (learning and memory deficits) and peripheral (motor dysfunction) neurotoxic effects at concentrations/doses similar to those of PCBs. The cellular and molecular mechanisms for these neurotoxic effects are not fully understood; however, several studies have shown that PBDEs affect thyroid hormones, cause oxidative stress, and disrupt Ca(2+)-mediated signal transduction. Changes in these signal transduction pathways can lead to differential gene regulation with subsequent changes in protein expression, which can affect the development and function of the nervous system. Objective: In this study, we examined the protein expression profiles in the rat cerebellum and hippocampus following developmental exposure to a commercial PBDE mixture, DE-71. Methods: Pregnant Long-Evans rats were dosed perinatally with 0 or 30.6 mg/kg/day of DE-71 from gestation day 6 through sampling on postnatal day 14. Proteins from the cerebellum and hippocampus were extracted, expression differences were detected by two-dimensional difference gel electrophoresis, and proteins were identified by tandem mass spectrometry. Protein network interaction analysis was performed using Ingenuity® Pathway Analysis, and the proteins of interest were validated by Western blotting. Results: Four proteins were significantly differentially expressed in the cerebellum following DE-71 exposure, whereas 70 proteins were significantly differentially expressed in the hippocampus. Of these proteins, 4 from the cerebellum and 47 from the hippocampus, identifiable by mass spectrometry, were found to have roles in mitochondrial energy metabolism, oxidative stress, apoptosis, calcium signaling, and growth of the nervous system. Conclusions: Results suggest that changes in energy metabolism and processes related to neuroplasticity and growth may be involved in the developmental neurotoxicity of PBDEs. Citation: Kodavanti PR, Royland JE, Osorio C, Winnik WM, Ortiz P, Lei L, Ramabhadran R, Alzate O. 2015. Developmental exposure to a commercial PBDE mixture: effects on protein networks in the cerebellum and hippocampus of rats. Environ Health Perspect 123:428–436; http://dx.doi.org/10.1289/ehp.140850