Erythropoietin shows gender dependent positive effects on social deficits, learning/memory impairments, neuronal loss and neuroinflammation in the lipopolysaccharide induced rat model of autism
Introduction
Autism spectrum disorder (ASD) is a neurodevelopmental disorder with early onset symptoms characterized by deficits in social and communicative skills, repetitive behaviors and/or restricted areas of interest (Vahia 2013). With a drastic increase in its prevalence over the few decades, ASD is now seen one in every 100 individuals and affects males more than females (Fombonne 2009). The etiology of ASD is poorly understood and tend to be complex and heterogenous with considerable amount of variation from one individual to another (Huguet et al. 2016; Hallmayer et al. 2011). In a study, it is reported that while genetic alterations may explain %35–40 of the cases; environmental factors during the different periods of brain development may cover the remaining cases of ASD. Neuroimmune alterations and inflammatory processes during brain development may contribute to the etiology of ASD (Hallmayer et al. 2011). In lipopolysaccharide induced rat model of autism, a well-known maternal immune activation model of ASD, it is shown that maternal immune activation during pregnancy may alter the expression of different pro- and anti-inflammatory cytokines in the developing brain and associated with abnormalities of neuronal proliferation, differentiation, maturation and neurodegeneration in different areas of cerebral cortex and hippocampus which eventually lead to an ASD-like phenotype (Boksa 2010; Ornoy et al. 2019). In animal studies, LPS administration to the pregnant rodents at the 10th gestational day is known to yield autism-like behavior in the offspring, with males being affected more severely. LPS exposed rats tend to display deficits in communicative and social skills, memory impairments and repetitive/restrictive behaviors (Kirsten et al. 2010).
Erythropoietin (EPO) is a glycoprotein hormone and has an important role in neurogenesis, along with its well-known role for erythropoiesis (Dhir 2010). Both EPO and its receptors are expressed in various regions of the fetal brain including hippocampus, internal capsule, cerebral cortex and midbrain (Frymoyer et al. 2017; Dhir 2010). Administration of human recombinant EPO is shown to have neuroprotective and neurotrophic effects in various clinical and non-clinical studies of different neuropsychiatric disorders including Alzheimer's disease, traumatic brain injury, epilepsy, neuropathies and multiple sclerosis (Sargin et al. 2010; Othman et al. 2018). In animal studies, it is shown that EPO exert its neuroprotective and neurotrophic effects by different mechanisms of action. Along with its anti-inflammatory, anti-excitotoxic and anti-oxidant properties, it also has modulatory roles on the processes of neurogenesis, angiogenesis and programmed cell death (Maiese 2016). It is also associated with improved performance on cognitive tasks of memory and learning, as well as increased expression of long term potentiation in hippocampus(Kamal et al. 2011).
While different agents with neuroprotective properties such as Vitamin D and fingolimod (Vuillermot et al. 2017; Wu et al. 2017) were studied on animal models of ASD and shown to be ameliorating the symptoms of ASD, to the best of authors knowledge, there is no study evaluated the effects of EPO on the social deficits, learning and memory impairments, neuronal loss and neuroinflammation in the lipopolysaccharide induced rat model of autism. In this study, we aimed to evaluate the effects of EPO in the lipopolysaccharide induced rat model of autism in terms of social deficits, learning and memory impairments, as well as, their neurochemical and histopathological correlates.
Section snippets
Animals
Sixteen female and 6 male Sprague Dawley adult rats (238 ± 10 g) were included in the study. The rats were housed in plastic cages and maintained under standard conditions with 12-h light/dark cycles at room temperature (22 ± 2 °C). All animal studies strictly adhered to the animal experiment guidelines as designated by the Institutional Animal Care and Ethics Committee.
Study design
Female rats were randomly distributed into two groups: Group A (control, n = 8) and Group B (LPS induced group n = 8) group.
Statistical analysis
Statistical evaluation was performed using SPSS version 15.0 for Windows (SPSS Inc., Chicago, IL, USA). Shapiro-Wilk's W and Levene's tests were used to check the normality and the homogeneity of variance, respectively. The results are presented as mean ± standard error of the mean (SEM). The value of p < .05 was accepted as statistically significant.
Results
A total of 48 rats exposed to % 0.9 NaCl saline or LPS were included in this study (8 male and 8 female rats exposed to % 0.9 NaCl saline as the control group; 16 male and 16 female rats exposed to LPS as the study group). Rats in the study arm were further divided into four groups and treated with saline or EPO (Group 1: 8 male rats LPS-exposed and saline treated; Group 2: 8 female rats LPS-exposed and saline treated; Group 3: 8 male rats LPS-exposed and EPO treated; Group 4: 8 male rats
Discussion
In this study, we found some beneficial effects of EPO, especially in male rats, on ASD-like symptoms, learning and memory processes at the levels of behavior and neurochemistry in a lipopolysaccharide induced rat model of autism. Anti-inflammatory effects of EPO, as evidenced by the findings of our study (lower level of TNF-α and lower number of GFAP-positive neurons in the hippocampus and increased frontal cortical thickness), may be helpful in explaining the beneficial effects of this
Declaration of competing interest
all the authors declares that there is no conflict of interests.
Author Contribution Statement.
VS: conceived and designed research, wrote the manuscript, Conceptualization. MAE and AA: Data curation, conducted experiments, wrote the manuscript AM and OE: Formal analysis, conducted experiments, edited the text. All authors read and approved the manuscript.
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