Myocardial nerve fibers are preserved in MPTP-treated mice, despite cardiac sympathetic dysfunction

Pathophysiological significance of increased α-synuclein deposition in sympathetic nerves in Parkinson's disease: a post-mortem observational study

Background

Parkinson’s disease (PD) is characterized by intra-neuronal deposition of the protein α-synuclein (α-syn) and by deficiencies of the catecholamines dopamine and norepinephrine (NE) in the brain and heart. Accumulation of α-syn in sympathetic noradrenergic nerves may provide a useful PD biomarker; however, whether α-syn buildup is pathophysiological has been unclear. If it were, one would expect associations of intra-neuronal α-syn deposition with catecholaminergic denervation and with decreased NE contents in the same samples.

Methods

We assayed immunoreactive α-syn and tyrosine hydroxylase (TH, a marker of catecholaminergic innervation) concurrently with catecholamines in coded post-mortem scalp skin, submandibular gland (SMG), and apical left ventricular myocardial tissue samples from 14 patients with autopsy-proven PD and 12 age-matched control subjects who did not have a neurodegenerative disease.

Results

The PD group had increased α-syn in sympathetic noradrenergically innervated arrector pili muscles (5.7 times control, P < 0.0001), SMG (35 times control, P = 0.0011), and myocardium (11 times control, P = 0.0011). Myocardial TH in the PD group was decreased by 65% compared to the control group (P = 0.0008), whereas the groups did not differ in TH in either arrector pili muscles or SMG. Similarly, myocardial NE was decreased by 92% in the PD group (P < 0.0001), but the groups did not differ in NE in either scalp skin or SMG.

Conclusions

PD entails increased α-syn in skin, SMG, and myocardial tissues. In skin and SMG, augmented α-syn deposition in sympathetic nerves does not seem to be pathogenic. The pathophysiological significance of intra-neuronal α-syn deposition appears to be organ-selective and prominent in the heart.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-022-00289-y.

Cardiac Changes in Parkinson's Disease: Lessons from Clinical and Experimental Evidence

Dysautonomia is a common non-motor symptom in Parkinson's disease (PD). Most dysautonomic symptoms appear due to alterations in the peripheral nerves of the autonomic nervous system, including both the sympathetic and parasympathetic nervous systems. The degeneration of sympathetic nerve fibers and neurons leads to cardiovascular dysfunction, which is highly prevalent in PD patients. Cardiac alterations such as orthostatic hypotension, heart rate variability, modifications in cardiogram parameters and baroreflex dysfunction can appear in both the early and late stages of PD, worsening as the disease progresses. In PD patients it is generally found that parasympathetic activity is decreased, while sympathetic activity is increased. This situation gives rise to an imbalance of both tonicities which might, in turn, promote a higher risk of cardiac damage through tachycardia and vasoconstriction. Cardiovascular abnormalities can also appear as a side effect of PD treatment: L-DOPA can decrease blood pressure and aggravate orthostatic hypotension as a result of a negative inotropic effect on the heart. This unwanted side effect limits the therapeutic use of L-DOPA in geriatric patients with PD and can contribute to the number of hospital admissions. Therefore, it is essential to define the cardiac features related to PD for the monitorization of the heart condition in parkinsonian individuals. This information can allow the application of intervention strategies to improve the course of the disease and the proposition of new alternatives for its treatment to eliminate or reverse the motor and non-motor symptoms, especially in geriatric patients.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

Cardiac sympathetic innervation in the MPTP non-human primate model of Parkinson disease

PURPOSE

Systemic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces degeneration of dopaminergic neurons and reproduces the motor features of Parkinson disease (PD); however, the effect of MPTP on extranigral structures has been poorly studied. The aim of this research was to study the cardiac sympathetic innervation of control and MPTP-treated monkeys in order to describe the influence of MPTP toxicity on cardiac tissue.

METHODS

Eight monkeys were included in the study and divided into two groups, four monkeys serving as controls and four forming the MPTP group. Sections from the anterior left ventricle were immunohistochemically examined to characterize the sympathetic fibers of cardiac tissue. The intensity of immunoreactivity in the nerve fibers was quantitatively analyzed using ImageJ software.

RESULTS

As occurs in PD, the sympathetic peripheral nervous system is affected in MPTP-treated monkeys. The percentage of tyrosine hydroxylase immunoreactive fibers in the entire fascicle area was markedly lower in the MPTP group (24.23%) than the control group (35.27%) (p < 0.05), with preservation of neurofilament immunoreactive fibers in the epicardium of MPTP-treated monkeys. Alpha-synuclein deposits were observed in sections of the anterior left ventricle of MPTP-treated monkeys but not in control animals, whereas phosphorylated synuclein aggregates were not observed in either controls or MPTP-treated monkeys.

CONCLUSION

The peripheral autonomic system can also be affected by neurotoxins that specifically inhibit mitochondrial complex I.

Distribution of oxidized DJ-1 in Parkinson's disease-related sites in the brain and in the peripheral tissues: effects of aging and a neurotoxin

DJ-1 plays an important role in antioxidant defenses, and a reactive cysteine at position 106 (Cys106) of DJ-1, a critical residue of its biological function, is oxidized under oxidative stress. DJ-1 oxidation has been reported in patients with Parkinson's disease (PD), but the relationship between DJ-1 oxidation and PD is still unclear. In the present study using specific antibody for Cys106-oxidized DJ-1 (oxDJ-1), we analyzed oxDJ-1 levels in the brain and peripheral tissues in young and aged mice and in a mouse model of PD induced using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). OxDJ-1 levels in the brain, heart, and skeletal muscle were high compared with other tissues. In the brain, oxDJ-1 was detected in PD-related brain sites such as the substantia nigra (SN) of the midbrain, olfactory bulb (OB), and striatum. In aged wild-type mice, oxDJ-1 levels in the OB, striatum, and heart tended to decrease, while those in the skeletal muscle increased significantly. Expression of dopamine-metabolizing enzymes significantly increased in the SN and OB of aged DJ-1-/- mice, accompanied by a complementary increase in glutathione peroxidase 1. MPTP treatment concordantly changed oxDJ-1 levels in PD-related brain sites and heart. These results indicate that the effects of physiological metabolism, aging, and neurotoxin change oxDJ-1 levels in PD-related brain sites, heart, and skeletal muscle where mitochondrial load is high, suggesting a substantial role of DJ-1 in antioxidant defenses and/or dopamine metabolism in these tissues.

Serum Tyrosine-to-Phenylalanine Ratio is Low in Parkinson's Disease

BACKGROUND

Noninvasive biomarkers for Parkinson's disease (PD) are currently unavailable.

OBJECTIVE

To search for a biomarker unique to PD in sweat and serum.

METHODS

Sweat samples in 42 PD patients and 16 controls were analyzed using liquid chromatography/mass spectrometry (LC/MS). The principal component analysis (PCA) and the orthogonal projections to latent structures (OPLS) analysis were employed. Serum Phe and Tyr levels were determined using the HPLC-fluorescence detection system in 28 de novo PD patients, 52 L-Dopa-treated PD patients, and 27 controls.

RESULTS

PCA and OPLS analyses of LC/MS of sweat samples revealed that Tyr, Phe, Leu (Ile), and Asp have high effect sizes to differentiate PD and controls. As Phe and Tyr are precursors of dopamine, we quantified the serum Phe and Tyr levels in de novo and treated PD patients, as well as in controls. Phe was high in de novo patients, but not in treated patients. In contrast, Tyr tended to be low in treated patients, but not in de novo patients. Tyr/Phe ratios were lower in both de novo and treated patients than in controls. The Tyr/Phe ratios were all higher than 0.82 in controls, whereas 49% of the de novo and treated patients had Tyr/Phe ratios less than 0.82. The low Tyr/Phe ratios were associated with male patients and low doses of entacapone. However, Tyr/Phe ratios were not different between male and female patients, and between patients with and without entacapone.

CONCLUSIONS

The low serum Tyr/Phe ratio differentiates PD from controls with sensitivity = 0.49, specificity = 1.00, positive predictive value = 1.00, and negative predictive value = 0.40.

Nonmotor Symptoms in Experimental Models of Parkinson's Disease

Nonmotor symptoms of Parkinson's disease (PD) range from neuropsychiatric, cognitive to sleep and sensory disorders and can arise from the disease process as well as from drug treatment. The clinical heterogeneity of nonmotor symptoms of PD is underpinned by a wide range of neuropathological and molecular pathology, affecting almost the entire range of neurotransmitters present in brain and the periphery. Understanding the neurobiology and pathology of nonmotor symptoms is crucial to the effective treatment of PD and currently a key unmet need. This bench-to-bedside translational concept can only be successful if robust animal models of PD charting the genesis and natural history of nonmotor symptoms can be devised. Toxin-based and transgenic rodent and primate models of PD have given us important clues to the underlying basis of motor symptomatology and in addition, can provide a snapshot of some nonmotor aspects of PD, although the data are far from complete. In this chapter, we discuss some of the nonmotor aspects of the available experimental models of PD and how the development of robust animal models to understand and treat nonmotor symptoms needs to become a research priority.

Non-motor features of Parkinson disease

Many of the motor symptoms of Parkinson disease (PD) can be preceded, sometimes for several years, by non-motor symptoms that include hyposmia, sleep disorders, depression and constipation. These non-motor features appear across the spectrum of patients with PD, including individuals with genetic causes of PD. The neuroanatomical and neuropharmacological bases of non-motor abnormalities in PD remain largely undefined. Here, we discuss recent advances that have helped to establish the presence, severity and effect on the quality of life of non-motor symptoms in PD, and the neuroanatomical and neuropharmacological mechanisms involved. We also discuss the potential for the non-motor features to define a prodrome that may enable the early diagnosis of PD.

Cardiac sympathetic denervation in 6-OHDA-treated nonhuman primates

Cardiac sympathetic neurodegeneration and dysautonomia affect patients with sporadic and familial Parkinson's disease (PD) and are currently proposed as prodromal signs of PD. We have recently developed a nonhuman primate model of cardiac dysautonomia by iv 6-hydroxydopamine (6-OHDA). Our in vivo findings included decreased cardiac uptake of a sympathetic radioligand and circulating catecholamines; here we report the postmortem characterization of the model. Ten adult rhesus monkeys (5–17 yrs old) were used in this study. Five animals received 6-OHDA (50 mg/kg iv) and five were age-matched controls. Three months post-neurotoxin the animals were euthanized; hearts and adrenal glands were processed for immunohistochemistry. Quantification of immunoreactivity (ir) of stainings was performed by an investigator blind to the treatment group using NIH ImageJ software (for cardiac bundles and adrenals, area above threshold and optical density) and MBF StereoInvestigator (for cardiac fibers, area fraction fractionator probe). Sympathetic cardiac nerve bundle analysis and fiber area density showed a significant reduction in global cardiac tyrosine hydroxylase-ir (TH; catecholaminergic marker) in 6-OHDA animals compared to controls. Quantification of protein gene protein 9.5 (pan-neuronal marker) positive cardiac fibers showed a significant deficit in 6-OHDA monkeys compared to controls and correlated with TH-ir fiber area. Semi-quantitative evaluation of human leukocyte antigen-ir (inflammatory marker) and nitrotyrosine-ir (oxidative stress marker) did not show significant changes 3 months post-neurotoxin. Cardiac nerve bundle α-synuclein-ir (presynaptic protein) was reduced (trend) in 6-OHDA treated monkeys; insoluble proteinase-K resistant α-synuclein (typical of PD pathology) was not observed. In the adrenal medulla, 6-OHDA monkeys had significantly reduced TH-ir and aminoacid decarboxylase-ir. Our results confirm that systemic 6-OHDA dosing to nonhuman primates induces cardiac sympathetic neurodegeneration and loss of catecholaminergic enzymes in the adrenal medulla, and suggests that this model can be used as a platform to evaluate disease-modifying strategies aiming to induce peripheral neuroprotection.

Treadmill gait analysis characterizes gait alterations in Parkinson's disease and amyotrophic lateral sclerosis mouse models

Guillot, Asress, Richardson, Glass, and Miller (2008) recently reported that treadmill gait analysis does not detect motor deficits in animal models of Parkinson's disease (PD) or amyotrophic lateral sclerosis (ALS). The authors studied aged C57BL/6J mice administered the neurotoxin 1-methyl 4-phenyl 1-, 2-, 3-, 6-tetrahydropyridine to model PD, and a small number of presymptomatic superoxide dismutase 1 G93A mice to study ALS. Several key issues merit discussion to put their observations in perspective. An increasing number of research groups are applying treadmill gait analysis to their rodent models of numerous movement disorders. The conclusions Guillot et al. drew undermine the potential importance of the paradigm of treadmill gait analysis for understanding and treating PD and ALS.

Multipoint analysis of reduced (125)I-meta-iodobenzylguanidine uptake and norepinephrine turnover in the hearts of mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydroxypyridine-induced parkinsonism

INTRODUCTION

(125)I-Meta-iodobenzylguanidine (MIBG) cardiac uptake is reduced in mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydroxypyridine (MPTP)-induced parkinsonism, although the cause of disturbance of norepinephrine (NE) turnover is unclear.

METHODS

C57BL6 mice (15 weeks old) were divided into six groups (n=14 each) according to the timing of MPTP injection (40 mg/kg) before (125)I-MIBG: Group A, control (no MPTP injection); Group B, 1 day; Group C, 4 days; Group D, 7 days; Group E, 21 days; Group F, 7, 14 and 21 days. (125)I-MIBG (0.185 MBq) was injected and the cardiac percentage injected dose per gram of tissue (%ID/g), dopamine (DA) and NE concentrations were measured. The cardiac maximal binding potential (B(max)) of NE transporter (NET) was also calculated in 20 mice per group.

RESULTS

The %ID/g of B, C, D, E and F mice were significantly lower than in A; those of C, D and E were significantly higher than in B; and that of F was significantly lower than in E. The DA concentrations were similar among all groups. The NE concentrations of B, C and F mice were significantly lower than in A, while those of C, D, E and F were significantly higher than in B, and that of F was significantly lower than in E. The B(max) of NET in B was significantly lower than in A.

CONCLUSIONS

Thus, MPTP causes rapid reductions in cardiac (125)I-MIBG uptake and B(max) of NET, followed by partial recovery of (125)I-MIBG uptake. Changes in cardiac (125)I-MIBG uptake and NE turnover were closely related in postganglionic cardiac sympathetic nerve terminals in mice with MPTP-induced parkinsonism.