Effects of Simultaneous Exposure to a Western Diet and Wheel-Running Training on Brain Energy Metabolism in Female Rats

BACKGROUND

In the pathogenesis of central nervous system disorders (e.g., neurodegenerative), an important role is attributed to an unhealthy lifestyle affecting brain energy metabolism. Physical activity in the prevention and treatment of lifestyle-related diseases is getting increasing attention.

METHODS

We performed a series of assessments in adult female Long Evans rats subjected to 6 weeks of Western diet feeding and wheel-running training. A control group of lean rats was fed with a standard diet. In all experimental groups, we measured physiological parameters (animal weights, body composition, serum metabolic parameters). We assessed the impact of simultaneous exposure to a Western diet and wheel-running on the cerebrocortical protein expression (global proteomic profiling), and in the second part of the experiment, we measured the cortical levels of protein related to brain metabolism (Western blot).

RESULTS

Western diet led to an obese phenotype and induced changes in the serum metabolic parameters. Wheel-running did not reduce animal weights or fat mass but significantly decreased serum glucose level. The global proteome analysis revealed that the altered proteins were functionally annotated as they were involved mostly in metabolic pathways. Western blot analysis showed the downregulation of the mitochondrial protein-Acyl-CoA dehydrogenase family member 9, hexokinase 1 (HK1)-enzyme involved in principal glucose metabolism pathways and monocarboxylate transporter 2 (MCT2). Wheel-running reversed this decline in the cortical levels of HK1 and MCT2.

CONCLUSION

The cerebrocortical proteome is affected by a combination of physical activity and Western diet in female rats. An analysis of the cortical proteins involved in brain energy metabolism provides a valuable basis for the deeper investigation of changes in the brain structure and function induced by simultaneous exposure to a Western diet and physical activity.

Upregulation of hepatic autophagy under nutritional ketosis

Many of the metabolic effects evoked by the ketogenic diet mimic the actions of fasting and the benefits of the ketogenic diet are often attributed to these similarities. Since fasting is a potent autophagy inductor in vivo and in vitro it has been hypothesized that the ketogenic diet may upregulate autophagy. The aim of the present study was to provide a comprehensive evaluation of the influence of the ketogenic diet on the hepatic autophagy. C57BL/6N male mice were fed with two different ketogenic chows composed of fat of either animal or plant origin for 4 weeks. To gain some insight into the time frame for the induction of autophagy on the ketogenic diet, we performed a short-term experiment in which animals were fed with ketogenic diets for only 24 or 48 h. The results showed that autophagy is upregulated in the livers of animals fed with the ketogenic diet. Moreover, the size of the observed effect was likely dependent on the diet composition. Subsequently, the markers of regulatory pathways that may link ketogenic diet action to autophagy were measured, i.e., the activity of mTORC1, activation of AMPK, and the levels of SIRT1, p53, and FOXO3. Overall, observed treatment-specific effects including the upregulation of SIRT1 and downregulation of FOXO3 and p53. Finally, a GC/MS analysis of the fatty acid composition of animals' livers and the chows was performed in order to obtain an idea about the presence of specific compounds that may shape the effects of ketogenic diets on autophagy.

The behavioral and molecular evaluation of effects of social instability stress as a model of stress-related disorders in adult female rats

The study aimed to test the hypotheses that chronic social instability stress (CSIS) alters behavioral and physiological parameters and expression of selected genes important for stress response and social behaviors. Adult female Sprague-Dawley rats were subjected to the 4-week CSIS procedure, which involves unpredictable rotation between phases of isolation and overcrowding. Behavioral analyses (Experiment 1) were performed on the same rats before and after CSIS (n = 16) and physiological and biochemical measurements (Experiment 2) were made on further control (CON; n = 7) and stressed groups (CSIS; n = 8). Behaviors in the open field test (locomotor and exploratory activities) and elevated-plus maze (anxiety-related behaviors) indicated anxiety after CSIS. CSIS did not alter the physiological parameters measured, i.e. body weight gain, regularity of estrous cycles, and circulating concentrations of stress hormones and sex steroids. QRT-PCR analysis of mRNA expression levels was performed on amygdala, hippocampus, prefrontal cortex (PFC), and hypothalamus. The main finding is that CSIS alters the mRNA levels for the studied genes in a region-specific manner. Hence, expression of POMC (pro-opiomelanocortin), AVPR1a (arginine vasopressin receptor), and OXTR (oxytocin receptor) significantly increased in the amygdala following CSIS, while in PFC and/or hypothalamus, POMC, AVPR1a, AVPR1b, OXTR, and ERβ (estrogen receptor beta) expression decreased. CSIS significantly reduced expression of CRH-R1 (corticotropin-releasing hormone receptor type 1) in the hippocampus. The directions of change in gene expression and the genes and regions affected indicate a molecular basis for the behavior changes. In conclusion, CSIS may be valuable for further analyzing the neurobiology of stress-related disorders in females.

The modification of the ketogenic diet mitigates its stunting effects in rodents

The high-fat and low-carbohydrate ketogenic diet (HFKD) is extensively studied within the fields of numerous diseases, including cancer and neurological disorders. Since most studies incorporate animal models, ensuring the quality of ketogenic rodent diets is important, both in the context of laboratory animal welfare as well as for the accuracy of the obtained results. In this study we implemented a modification to a commonly used ketogenic rodent chow by replacing non-resorbable cellulose with wheat bran. We assessed the effects of month-long treatment with either the unmodified or the modified HFKD on the growth and development of young male rats. Daily body weight, functional performance, and brain morphometric parameters were assessed to evaluate the influence of both applied diets on rodent development. Our results revealed that the unmodified ketogenic chow induced strong side effects that included weakness, emaciation, and brain undergrowth concomitant to growth inhibition. However, application of the ketogenic chow supplemented with wheat bran suppressed these adverse side effects, which was associated with the restoration of insulin-like growth factor 1 and a decrease in corticosterone levels. We have also shown that the advantageous results of the modified HFKD are not species- or sex-specific. Our data indicate that the proposed HFKD modification even allows for its application in young animals, without causing detrimental side effects.

Alterations in VEGF expression induced by antidepressant drugs in female rats under chronic social stress

Vascular endothelial growth factor (VEGF) is thought to serve a role in neurogenesis and the stress response. Although a definite link between the action of antidepressants and VEGF has not been identified, it is assumed that VEGF, as a neurotrophic factor, serves an important role in the effects of antidepressant treatment. To examine this, the present study subjected adult female rats to four weeks of social instability stress and measured the effect of antidepressant treatment on the expression of VEGF. Firstly, endocrine markers of stress and body weight were measured in parallel with behavioral tests prior to and following subjection to stress. Then, the effect of 28-day daily treatment with desipramine (DMI; 10 mg/kg), fluoxetine (5 mg/kg) or tianeptine (10 mg/kg) on the number of copies of VEGF mRNA in the amygdala, hippocampus and hypothalamus, and on serum VEGF protein levels, of rats subjected to chronic stress was determined. In addition, the weight of the adrenal glands was measured following subjection to stress. Exposure to chronic stress was found to increase the rats' sucrose preference, and diminish their tendency for general exploration and time spent in the open. The relative adrenal weights of the stressed rats were significantly increased compared with the control. Plasma concentrations of corticosterone and adrenocorticotropic hormone were not significantly augmented. In addition, the present study identified that stress elevated VEGF mRNA expression in all studied neural structures. Furthermore, the results identified that the stress-induced increase in VEGF mRNA expression in the amygdala and hypothalamus was attenuated by long-term administration of DMI. Conversely, a decrease in serum VEGF concentration was observed in stressed rats, which was not reversed by treatment with antidepressants. In conclusion, the current study suggests that under conditions of stress, VEGF serves a role in the mechanism of action of DMI, through modulating activity of the norepinephrine system.

Expression of a novel splicing variant of Pcp2 in closely related laboratory rodents

Purkinje cell protein-2 (PCP2), also known as L7, is a member of the GoLoco protein family with highly cell-specific expression, being restricted to cerebellar Purkinje cells and retinal bipolar neurons in various species. However, its function in these tissues is unknown. Previous studies have suggested that PCP2 is a guanine nucleotide dissociation inhibitor, or a guanine nucleotide exchange factor. The Pcp2 gene is known to have many splice variants in both cerebellar Purkinje cells and retinal bipolar neurons. Here, we tested the hypothesis that a novel Pcp2 splice variant is conserved in closely related laboratory rodents (mice, rats, and hamsters). After analyzing alternative splicing of this gene in the Purkinje cells and retinas of these rodent species, we confirmed the presence of the novel longer transcript in mice. However, assessment of Pcp2 transcripts using polymerase chain reaction amplification of complementary DNA revealed this long splice variant containing the additional exon 3B to be absent from rats and hamsters. Thus, the novel Pcp2 transcript is particular to mouse cerebellar Purkinje cells and retinal bipolar neurons. It is likely to have arisen in this species, as a result of spontaneous mutation or de novo rearrangements. This gene presumably serves a very specific and, as yet, unknown function in the eyes and/or Purkinje cells of mice.