Influence of age and gender on cytokine expression in a murine model of Parkinson's disease

Should We Consider Neurodegeneration by Itself or in a Triangulation with Neuroinflammation and Demyelination? The Example of Multiple Sclerosis and Beyond

Neurodegeneration is preeminent in many neurological diseases, and still a major burden we fail to manage in patient's care. Its pathogenesis is complicated, intricate, and far from being completely understood. Taking multiple sclerosis as an example, we propose that neurodegeneration is neither a cause nor a consequence by itself. Mitochondrial dysfunction, leading to energy deficiency and ion imbalance, plays a key role in neurodegeneration, and is partly caused by the oxidative stress generated by microglia and astrocytes. Nodal and paranodal disruption, with or without myelin alteration, is further involved. Myelin loss exposes the axons directly to the inflammatory and oxidative environment. Moreover, oligodendrocytes provide a singular metabolic and trophic support to axons, but do not emerge unscathed from the pathological events, by primary myelin defects and cell apoptosis or secondary to neuroinflammation or axonal damage. Hereby, trophic failure might be an overlooked contributor to neurodegeneration. Thus, a complex interplay between neuroinflammation, demyelination, and neurodegeneration, wherein each is primarily and secondarily involved, might offer a more comprehensive understanding of the pathogenesis and help establishing novel therapeutic strategies for many neurological diseases and beyond.

Inflammation as common link to progressive neurological diseases

Life expectancy has increased immensely over the past decades, bringing new challenges to the health systems as advanced age increases the predisposition for many diseases. One of those is the burden of neurologic disorders. While many hypotheses have been placed to explain aging mechanisms, it has been widely accepted that the increasing pro-inflammatory status with advanced age or "inflammaging" is a main determinant of biological aging. Furthermore, inflammaging is at the cornerstone of many age-related diseases and its involvement in neurologic disorders is an exciting hypothesis. Indeed, aging and neurologic disorders development in the elderly seem to share some basic pathways that fundamentally converge on inflammation. Peripheral inflammation significantly influences brain function and contributes to the development of neurological disorders, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Understanding the role of inflammation in the pathogenesis of progressive neurological diseases is of crucial importance for developing effective treatments and interventions that can slow down or prevent disease progression, therefore, decreasing its social and economic burden.

Impact of Sex on Neuroimmune contributions to Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. Inflammation has been observed in both the idiopathic and familial forms of PD. Importantly, PD is reported more often in men than in women, men having at least 1.5- fold higher risk to develop PD than women. This review summarizes the impact of biological sex and sex hormones on the neuroimmune contributions to PD and its investigation in animal models of PD. Innate and peripheral immune systems participate in the brain neuroinflammation of PD patients and is reproduced in neurotoxin, genetic and alpha-synuclein based models of PD. Microglia and astrocytes are the main cells of the innate immune system in the central nervous system and are the first to react to restore homeostasis in the brain. Analysis of serum immunoprofiles in female and male control and PD patients show that a great proportion of these markers differ between male and female. The relationship between CSF inflammatory markers and PD clinical characteristics or PD biomarkers shows sex differences. Conversely, in animal models of PD, sex differences in inflammation are well documented and the beneficial effects of endogenous and exogenous estrogenic modulation in inflammation have been reported. Targeting neuroinflammation in PD is an emerging therapeutic option but gonadal drugs have not yet been investigated in this respect, thus offering new opportunities for sex specific treatments.

Effect of sex and gonadectomy on brain MPTP toxicity and response to dutasteride treatment in mice

The main neuropathological feature of Parkinson's disease (PD) is degeneration of dopamine (DA) neurons in the substantia nigra (SN); PD prevalence is higher in men, suggesting a role of sex hormones in neuroprotection. This study sought the effects of sex hormones in the brain in a mouse model of PD and modulation of steroid metabolism/synthesis with the 5α-reductase inhibitor dutasteride shown to protect 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) male mice. Male and female mice were gonadectomized (GDX) or SHAM operated. They were treated with vehicle or dutasteride (5 mg/kg) for 10 days and administered a low dose of MPTP (5.5 mg/kg) or saline on the 5th day to model early PD; brains were collected thereafter. Striatal measures of the active metabolite 1-methyl-4-phenylpyridinium (MPP+) contents showed no difference supporting an effect of the experimental conditions investigated. In SHAM MPTP male mice loss of striatal DA and metabolites, DA transporter (DAT) and vesicular monoamine transporter 2 (VMAT2) specific binding in the striatum and SN was prevented by dutasteride treatment; these changes were inversely correlated with glial fibrillary acidic protein (GFAP, an astrogliosis marker) levels. In SHAM female mice MPTP treatment had little or no effect on striatal and SN DA markers and GFAP levels whereas GDX male and female mice showed a similar loss of striatal DA markers and increase of GFAP. No effect of dutasteride treatment was observed in GDX male and female mice. In conclusion, sex differences in mice MPTP toxicity and response to dutasteride were observed that were lost upon gonadectomy implicating neuroinflammation.

Genetic Defects and Pro-inflammatory Cytokines in Parkinson's Disease

Parkinson's disease (PD) is a movement disorder attributed to the loss of dopaminergic (DA) neurons mainly in the substantia nigra pars compacta. Motor symptoms include resting tremor, rigidity, and bradykinesias, while non-motor symptoms include autonomic dysfunction, anxiety, and sleeping problems. Genetic mutations in a number of genes (e.g., LRRK2, GBA, SNCA, PARK2, PARK6, and PARK7) and the resultant abnormal activation of microglial cells are assumed to be the main reasons for the loss of DA neurons in PD with genetic causes. Additionally, immune cell infiltration and their participation in major histocompatibility complex I (MHCI) and/or MHCII-mediated processing and presentation of cytosolic or mitochondrial antigens activate the microglial cells and cause the massive generation of pro-inflammatory cytokines and chemokines, which are all critical for the propagation of brain inflammation and the neurodegeneration in PD with genetic and idiopathic causes. Despite knowing the involvement of several of such immune devices that trigger neuroinflammation and neurodegeneration in PD, the exact disease mechanism or the innovative biomarker that could detect disease severity in PD linked to LRRK2, GBA, SNCA, PARK2, PARK6, and PARK7 defects is largely unknown. The current review has explored data from genetics, immunology, and in vivo and ex vivo functional studies that demonstrate that certain genetic defects might contribute to microglial cell activation and massive generation of a number of pro-inflammatory cytokines and chemokines, which ultimately drive the brain inflammation and lead to neurodegeneration in PD. Understanding the detailed involvement of a variety of immune mediators, their source, and the target could provide a better understanding of the disease process. This information might be helpful in clinical diagnosis, monitoring of disease progression, and early identification of affected individuals.

ApoE isoform-specific differences in behavior and cognition associated with subchronic MPTP exposure

Parkinson's disease (PD) is characterized clinically by progressive motor dysfunction; overt parkinsonism is often preceded by prodromal symptoms including disturbances in the sleep–wake cycle. Up to 80% of patients with PD also develop dementia. In humans, there are three major apolipoprotein E isoforms: E2, E3, and E4. Increased rate of dementia in PD may be associated with E4 isoform. To better understand prodromal changes associated with E4, we exposed young (3–5 mo) male and female mice expressing E3 or E4 via targeted replacement to a subchronic dosage of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We hypothesized that E4 mice would be more susceptible to MPTP-related behavioral and cognitive changes. MPTP-treated E4 mice explored novel objects longer than genotype-matched saline-treated mice. In contrast, saline-treated E3 mice preferentially explored the novel object whereas MPTP-treated E3 mice did not and showed impaired object recognition. MPTP treatment altered swim speed of E4, but not E3, mice in the water maze compared to controls. Thus, E4 carriage may influence the preclinical symptoms associated with PD. Increased efforts are warranted to study early time points in this disease model.

Plasma IL-6 and IL-17A Correlate with Severity of Motor and Non-Motor Symptoms in Parkinson's Disease

The nature of the inflammatory response in Parkinson’s disease (PD) remains to be better understood. Here, we used highly sensitive Single Molecule Array (SIMOA) technology to measure the levels of the inflammatory mediators Interleukin 6 (IL-6), Interleukin 17A (IL-17A), Tumour Necrosis Factor α (TNFα) and Transforming Growth Factor β (TGFβ) in plasma from PD patients and age- and gender-matched healthy controls. We report that IL-17A correlates with non-motor symptoms (NMS) scores, while IL-6 positively correlates with motor scores. We found no correlations between cytokines and disease duration suggesting that IL-6 and IL-17A are associated with disease severity rather than disease duration in this cohort, furthermore IL-17A may be involved in the underlying pathophysiology of NMS in PD.

The assessment of possible gender-related effect of endogenous striatal alpha-tocopherol level on MPTP neurotoxicity in mice

Several studies supported an increased vulnerability of males regarding Parkinson's disease (PD) and its animal models, the background of which has not been exactly revealed, yet. In addition to hormonal differences, another possible factor behind that may be a female-predominant increase in endogenous striatal alpha-tocopherol (αT) level with aging, even significant at 16 weeks of age, previously demonstrated by the authors. Accordingly, the aim of the current study was the assessment whether this difference in striatal αT concentration may contribute to the above-mentioned distinct vulnerability of genders to nigrostriatal injury. Female and male C57Bl/6 mice at the age of 16 weeks were injected with 12 mg/kg body weight 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) 5 times at 2 h intervals or with saline. The levels of some biogenic amines (striatum) and αT (striatum and plasma) were determined by validated high performance liquid chromatography methods. Although the results proved previous findings, i.e., striatal dopamine decrease was less pronounced in females following MPTP treatment, and striatal αT level was significantly higher in female mice, the correlation between these 2 variables was not significant. Surprisingly, MPTP treatment did not affect striatal αT concentrations, but significantly decreased plasma αT levels without differences between genders. The current study, examining the possible role of elevated αT in female C57Bl/6 mice behind their decreased sensitivity to MPTP intoxication for the first time, was unable to demonstrate any remarkable connection between these 2 variables. These findings may further confirm that αT does not play a major role against neurotoxicity induced by MPTP.

Systemic Inflammation in Lewy Body Diseases: A Systematic Review

Few studies have investigated the role of inflammation in Lewy body dementia (LBD) and variable results have been found. We systematically reviewed the literature for evidence of systemic inflammatory changes in dementia with Lewy bodies and Parkinson disease dementia. Owing to the low number of studies we also included Parkinson disease. Key terms were used to search the relevant databases. Titles and abstracts were screened and potentially relevant articles were reviewed in full. References of included studies and relevant reviews were searched. The database search returned 2166 results, 46 of which were finally included in the systematic review. These studies showed a general increase in inflammatory markers in the peripheral blood, most notably interleukin-1β (IL-1β), tumor necrosis factor-α, IL-6, and IL-10. Studies examining cerebrospinal fluid found IL-1β, IL-6, and transforming growth factor-β1 to be particularly increased, and interferon-γ decreased. C-reactive protein levels were increased, particularly in Parkinson disease dementia. These results provide evidence that LBD is associated with an increased inflammatory response. Furthermore, there may be a stronger general inflammatory response in LBD than in Parkinson disease, while complex changes occur in the individual cytokines.

Sex influences in neurological disorders: case studies and perspectives

Beginning in the late 1980s and early 1990s, scientists and the public alike recognized that, for too long, women had been underrepresented in clinical trials. While much progress was made in the following decades, preclinical research still often ignores sex as a fundamental biological variable. Many neurological disorders, including multiple sclerosis and migraine, show strong sex differences in incidence and disease manifestation. In this commentary, we highlight case studies of neurological disorders affecting men and women to demonstrate the need for more such studies. Research conducted in these areas so far has shed light on the underlying mechanisms of the disease and offers the promise to help develop more personalized treatments for both men and women.

The influence of AAV2-mediated gene transfer of human IL-10 on neurodegeneration and immune response in a murine model of Parkinson's disease

BACKGROUND

The aim of this study was to examine the effect of AAV2-hIL-10 (vector containing cDNA for human interleukin 10) on dopaminergic system activity (measured as DA levels and TH mRNA expression in mouse striata), and other monoamine and amino acid neurotransmitters concentration as well as development of inflammatory processes (measured as TGF-β, IFN-γ and GFAP mRNA expression) in a murine MPTP neurotoxicant model of Parkinson's disease.

METHODS

Male C57BL/6 mice 12 months-old were used in this study. AAV2-hIL-10 vector was bilaterally administered into striatum at 14, 21 or 28 days prior to MPTP intoxication. Animals were sacrificed at 7 days following MPTP injection. The expression of hIL-10 (human interleukin 10) was examined by ELISA. Striatal monoamine and amino acid neurotransmitters were measured by HPLC method. TH, TGF-β, IFN-γ and GFAP mRNA expression was examined by RT-PCR method.

RESULTS

MPTP treatment dramatically reduced DA levels and decreased TH mRNA expression in mouse striata, effects that were significantly impeded by AAV2-hIL-10 administration prior to MPTP intoxication. AAV2-hIL-10 infusion increased IFN-γ, TGF-β and GFAP mRNA expression.

CONCLUSIONS

Our data suggest that the transfer of AAV2-hIL-10 into the striatum may play a neuroprotective role in the mouse MPTP model of PD and these effects are mediated by the anti-inflammatory action of IL-10.

gp130 cytokines stimulate proteasomal degradation of tyrosine hydroxylase via extracellular signal regulated kinases 1 and 2

Injury-induced cytokines act through gp130 in sympathetic neurons to suppress expression of tyrosine hydroxylase (TH) and other genes associated with noradrenergic transmission. These cytokines also trigger the local loss of TH in peri-infarct sympathetic axons after myocardial infarction, but altered gene expression cannot explain the selective loss of TH enzyme in one region of the heart. We hypothesized that inflammatory cytokines, which are highest near the infarct, stimulated local degradation of TH protein. We used cultured sympathetic neurons and neuroblastoma cells to test this hypothesis. The cytokines ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) suppressed TH content in both neurons and neuroblastoma cells. CNTF suppressed TH in a gp130-dependent manner, and decreased the half-life of TH protein by approximately 50%. CNTF stimulated the ubiquitination of TH in both neurons and neuroblastoma cells, and the proteasome inhibitors MG-132 and lactacystin prevented the CNTF-induced loss of TH protein. Inhibiting activation of extracellular signal regulated kinases 1&2 (ERK1/2) with U0126 prevented the CNTF-induced ubiquitination of TH and the associated decrease in protein half-life. Likewise, inhibiting ERK1/2 activation blunted the cytokine-stimulated loss of TH protein in sympathetic neurons, despite enhancing the loss of TH mRNA. These data suggest that gp130 cytokines stimulate proteasomal degradation of TH through an ERK1/2 dependent pathway, and may have important implications for local regulation of neurotransmission at sites of inflammation.

Role of CB1 cannabinoid receptors on GABAergic neurons in brain aging

Brain aging is associated with cognitive decline that is accompanied by progressive neuroinflammatory changes. The endocannabinoid system (ECS) is involved in the regulation of glial activity and influences the progression of age-related learning and memory deficits. Mice lacking the Cnr1 gene (Cnr1(-/-)), which encodes the cannabinoid receptor 1 (CB1), showed an accelerated age-dependent deficit in spatial learning accompanied by a loss of principal neurons in the hippocampus. The age-dependent decrease in neuronal numbers in Cnr1(-/-) mice was not related to decreased neurogenesis or to epileptic seizures. However, enhanced neuroinflammation characterized by an increased density of astrocytes and activated microglia as well as an enhanced expression of the inflammatory cytokine IL-6 during aging was present in the hippocampus of Cnr1(-/-) mice. The ongoing process of pyramidal cell degeneration and neuroinflammation can exacerbate each other and both contribute to the cognitive deficits. Deletion of CB1 receptors from the forebrain GABAergic, but not from the glutamatergic neurons, led to a similar neuronal loss and increased neuroinflammation in the hippocampus as observed in animals lacking CB1 receptors in all cells. Our results suggest that CB1 receptor activity on hippocampal GABAergic neurons protects against age-dependent cognitive decline by reducing pyramidal cell degeneration and neuroinflammation.

Sex differences in the injured brain

Observations obtained in human and in experimental models clearly demonstrate sex differences in degenerative events occurring in the central nervous system. The present review focuses on potential factors that may contribute to these sex-dimorphic features; in particular, morphological organization of the central nervous system and functional influence by neuroactive steroids, genes, and immune system are considered.

The impact of age and gender on the striatal astrocytes activation in murine model of Parkinson's disease

OBJECTIVE

The aim of the present study was to determine how aging and gender influence the response of astrocytes to 1-methyl-4-phenyl-1,2,3,6-tetrahydropiridine (MPTP) intoxication.

MATERIALS AND METHODS

To asses the MPTP-induced astrocytes activation in nigro-striatal system, we measured the temporal changes in mRNA and protein expression of the specific astrocytic marker, glial fibrillary acidic protein (GFAP; by RT-PCR and Western blot), in the striatum of male and female C57BL/6 mice (2 and 12-month old) after 6 h and 1, 3, 7, 14 and 21 days post-intoxication.

RESULTS

We observed the increases of GFAP mRNA level post-MPTP intoxication in both young and aging males only at early time points, whereas in females (both ages) also at later time points. We noticed maximal increase of GFAP protein content on the 3rd day post-intoxication in young and aged males, whereas in females at the 7-daytime point.

CONCLUSIONS

The present results provide additional information of potential relevance to understand the mechanisms of gender and age-related difference in susceptibility of nigro-striatal system to MPTP insult.

Gender differences on MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in C57BL/6 mice

The aim of this study was to investigate the impact of gender difference in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated animal model of Parkinson's disease (PD). In the present study, we investigated the time-dependent alterations of dopamine and its metabolites, striatal tyrosine hydroxylase (TH) protein, dopamine transporter (DAT) protein, glial fibrillary acidic protein (GFAP) protein and midbrain TH protein and motor function in male and female mice 5h and 1, 3 and 7 days after four administrations of MPTP (20mg/kg) at 2-h intervals. The present study showed that the decrease of dopamine, DOPAC (3,4-dihydroxyphenylacetic acid) and HVA (homovanillic acid) content in female mice was more pronounced than that in male animals 1, 3 and 7 days after MPTP treatment. Our Western blot analysis study also demonstrated that the decrease of both striatal and midbrain TH protein levels in female mice was more pronounced than that in male animals from 1 to 7 days after MPTP treatment. As compared to male mice, in contrast, the increase of striatal GFAP protein levels in female mice was observed from 5h to 7 days after MPTP treatment. Furthermore, the present study showed that motor deficits were found in both male and female mice 1 and 7 days after MPTP treatment. In the present study, moreover, the decrease of striatal DAT protein levels in female mice was more pronounced than that in male animals 1, 3 and 7 days after MPTP treatment. These results demonstrate that our administrations of MPTP at 2-h intervals can cause more severe damage in female mice as compared with male animals. The gender difference may be due to the decrease of DAT expression caused by MPTP. Thus our findings provide further valuable information for the pathogenesis of PD.

Interferon-gamma deficiency modifies the motor and co-morbid behavioral pathology and neurochemical changes provoked by the pesticide paraquat

In addition to nigrostriatal pathology and corresponding motor disturbances, Parkinson's disease (PD) is often characterized by co-morbid neuropsychiatric symptoms, most notably anxiety and depression. Separate lines of evidence indicate that inflammatory processes associated with microglial activation and cytokine release may be fundamental to the progression of both PD and its co-morbid psychiatric pathology. Accordingly, we assessed the contribution of the pro-inflammatory cytokine, interferon-gamma (IFN-gamma), to a range of PD-like pathology provoked by the ecologically relevant herbicide and dopamine (DA) toxin, paraquat. To this end, paraquat provoked overt motor impairment (reduced home-cage activity and impaired vertical climbing) and signs of anxiety-like behavior (reduced open field exploration) in wild-type but not IFN-gamma-deficient mice. Correspondingly, paraquat promoted somewhat divergent variations in neurochemical activity among wild-type and IFN-gamma null mice at brain sites important for both motor (striatum) and co-morbid affective pathologies (dorsal hippocampus, medial prefrontal cortex, and locus coeruleus). Specifically, the herbicide provoked a dosing regimen-dependent reduction in striatal DA levels that was prevented by IFN-gamma deficiency. In addition, the herbicide influenced serotonergic and noradrenergic activity within the dorsal hippocampus and medial prefrontal cortex; and elevated noradrenergic activity within the locus coeruleus. Although genetic ablation of IFN-gamma had relatively few effects on monoamine variations within the locus coeruleus and prefrontal cortex, loss of the pro-inflammatory cytokine did normalize the paraquat-induced noradrenergic alterations within the hippocampus. These findings further elucidate the functional implications of paraquat intoxication and suggest an important role for IFN-gamma in the striatal and motor pathology, as well as the co-morbid behavioral and hippocampal changes induced by paraquat.

Decreased inflammation and augmented expression of trophic factors correlate with MOG-induced neuroprotection of the injured nigrostriatal system in the murine MPTP model of Parkinson's disease

The response of the immune system during injury of the central nervous system may play a role in protecting neurons. We have previously reported that immunization with MOG 35-55 prior to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced injury of the dopaminergic system promotes less dopamine depletion and less dopaminergic damage of neurons in mice. In this study, we evaluate the influence of MOG immunization on the inflammatory reaction that occurs at the place of injury. C57Bl male mice, 2 and 12 months old, received i.p. injections of MPTP (40 mg/kg) and some groups animals also received an additional injection with myelin oligodendrocyte glycoprotein (MOG) 35-55 in CFA 6 days before MPTP administration. MPTP caused a common inflammatory reaction characterized by microglial activation, infiltration of T cells into the substantia nigra and striatum and increased expression of mRNA encoding pro-inflammatory cytokines (IL-1 beta, TNFalpha, INF gamma) and trophic factors (TGFbeta, GDNF). MOG immunization prior to MPTP administration significantly diminished the microglial reaction and reduced the levels of infiltrating CD8+ lymphocytes. The number of CD4+ T cells remained at the same level as in the MPTP group. Expression of pro-inflammatory cytokines was diminished. The mRNA expression of GDNF was significantly higher in the MOG pretreated mice relative to the MPTP group, both in the 2 month old and 12 month old groups. Since MOG immunization prior to MPTP intoxication appears to prevent nigrostriatal injury, the observed decrease of inflammation and increase of GDNF mRNA expression in the injured areas might represent one of the mechanisms of observed neuroprotection.

Age- and sex-differences in the nitric oxide synthase expression and dopamine concentration in the murine model of Parkinson's disease induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

Parkinson's disease (PD) is an age- and sex-related neurodegenerative disorder of unknown aetiology. The involvement of nitric oxide synthase (NOS) in the etiopathogenesis of PD is quite well documented. We decided to examine changes in dopamine (DA) levels as well as iNOS, nNOS, eNOS mRNA and protein expression in the striatum of C57BL male and female (2- and 12-month old) mice in the course of PD-related neurodegeneration induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The significantly decreased level of DA was previously observed in male than in female, irrespective of age. In young mice the recovery of DA was significantly greater in female compared to male mice. On the contrary, both in male and female old animals the low concentration of DA was extended up to 21 days post MPTP injection. The increases in iNOS protein expression post MPTP intoxication occurred more rapidly in male (young and old) than in female mice. The pattern of changes in iNOS protein expression was also different in young versus aged mice. nNOS protein expression increased earlier in young male than young female mice. No changes were observed in eNOS expression. In conclusion, our results support the hypothesis of the involvement of iNOS and nNOS, but not eNOS in neurodegenerative processes. Our findings suggest that age- and sex-differences in DA concentration and iNOS expression as well as sex-differences of nNOS expression after intoxication may depend on the increased susceptibility of males as well as older animals to toxic effect of MPTP and aggravated process of recovery in old brains.