From Molecules to Behavior in Long-Term Inorganic Mercury Intoxication: Unraveling Proteomic Features in Cerebellar Neurodegeneration of Rats

Abstract

Mercury is a severe environmental pollutant with neurotoxic effects, especially when exposed for long periods. Although there are several evidences regarding mercury toxicity, little is known about inorganic mercury (IHg) species and cerebellum, one of the main targets of mercury associated with the neurological symptomatology of mercurial poisoning. Besides that, the global proteomic profile assessment is a valuable tool to screen possible biomarkers and elucidate molecular targets of mercury neurotoxicity; however, the literature is still scarce. Thus, this study aimed to investigate the effects of long-term exposure to IHg in adult rats’ cerebellum and explore the modulation of the cerebellar proteome associated with biochemical and functional outcomes, providing evidence, in a translational perspective, of new mercury toxicity targets and possible biomarkers. Fifty-four adult rats were exposed to 0.375 mg/kg of HgCl2 or distilled water for 45 days using intragastric gavage. Then, the motor functions were evaluated by rotarod and inclined plane. The cerebellum was collected to quantify mercury levels, to assess the antioxidant activity against peroxyl radicals (ACAPs), the lipid peroxidation (LPO), the proteomic profile, the cell death nature by cytotoxicity and apoptosis, and the Purkinje cells density. The IHg exposure increased mercury levels in the cerebellum, reducing ACAP and increasing LPO. The proteomic approach revealed a total 419 proteins with different statuses of regulation, associated with different biological processes, such as synaptic signaling, energy metabolism and nervous system development, e.g., all these molecular changes are associated with increased cytotoxicity and apoptosis, with a neurodegenerative pattern on Purkinje cells layer and poor motor coordination and balance. In conclusion, all these findings feature a neurodegenerative process triggered by IHg in the cerebellum that culminated into motor functions deficits, which are associated with several molecular features and may be related to the clinical outcomes of people exposed to the toxicant.

Global Proteomic Profile of Aluminum-Induced Hippocampal Impairments in Rats: Are Low Doses of Aluminum Really Safe?

“…The proteomic data analyses were only possible due to the comparability between the samples within the same group, and the use of Protein Lynx GlobalSERVER software, robust software for data analyses, was able to determine the p values, hence the quantitative proteomic analysis, considering p < 0.05 for downregulated proteins and 1 − p > 0.95 for upregulated proteins. Detailed methodology is available elsewhere [ 11 , 66 , 86 ].…”

“…Al has no biological function in humans; moreover, prolonged exposure to Al may be associated with hematopoietic, skeletal, respiratory, immunological, neurological, and functional adverse effects [ 8 ]. Since Al-induced toxic effects are evidenced in vitro [ 9 ], in humans [ 10 ], and animal studies [ 11 ], this element has received considerable attention mainly due to its neurotoxic abilities. These effects are prominent and have been associated with neurodegenerative diseases, especially Alzheimer’s disease (AD) [ 12 , 13 ].…”

Methylmercury exposure during prenatal and postnatal neurodevelopment promotes oxidative stress associated with motor and cognitive damages in rats: an environmental-experimental toxicology study

“…This profile guarantees the translational value of this work, standing out in the current literature as a more realistic approach when compared to other studies. For instance, cerebellar cortex is one of the most affected regions in humans chronically contaminated by Hg (Eto et al [103] ), a pattern also observed in rats submitted to a long-term intoxication (Bittencourt et al [104] ). Therefore, although it is important to bear in mind that the physiological particularities between humans and rats should be considered when evaluating the results of studies using animal models [105] , this study took advantage of the improvement recommendations that were previously suggested to have a significant and differentiated translational value within the current literature.…”

Intrauterine and Postnatal Exposure to High Levels of Fluoride Is Associated with Motor Impairments, Oxidative Stress, and Morphological Damage in the Cerebellum of Offspring Rats

“…For evaluation of Purkinje cell density, the sections obtained by microtomy were stained by routine hematoxylin–eosin (HE) and then analyzed by light microscopy (Nikon Eclipse E200, Tokyo, Japan), using a grid corresponding to an area of 0.0625 mm 2 coupled to one of the eyepieces, using an objective lens with 40× magnification. At least three fields in the cerebellum per section and one section per animal of each group were analyzed to count the number of Purkinje neurons per field [ 49 ].…”