Spectrum of abnormalities of sympathetic tyrosine hydroxylase and alpha-synuclein in chronic autonomic failure

A pathophysiological biomarker combination separates Lewy body from non-Lewy body neurogenic orthostatic hypotension ​

PURPOSE

Neurogenic orthostatic hypotension (nOH) results from deficient reflexive delivery of norepinephrine to cardiovascular receptors in response to decreased cardiac venous return. Lewy body (LB) forms of nOH are characterized by low 18F-dopamine-derived radioactivity (a measure of cardiac noradrenergic deficiency), olfactory dysfunction by the University of Pennsylvania Smell Identification Test (UPSIT), and increased deposition of alpha-synuclein (α-syn) in dermal sympathetic noradrenergic nerves by the α-syn-tyrosine hydroxylase (TH) colocalization index. This observational, cross-sectional study explored whether combinations of these biomarkers specifically identify LB forms of nOH.

METHODS

Clinical laboratory data were reviewed from patients referred for evaluation at the National Institutes of Health for chronic autonomic failure between 2011 and 2023. The cutoff value for low myocardial 18F-dopamine-derived radioactivity was 6000 nCi-kg/cc-mCi, for olfactory dysfunction an UPSIT score ≤ 28, and for an increased α-syn-TH colocalization index ≥ 1.57.

RESULTS

A total of 44 patients (31 LB, 13 non-LB nOH) had data for all three biomarkers. Compared to the non-LB group, the LB nOH group had low myocardial 18F-dopamine-derived radioactivity, low UPSIT scores, and high α-syn-TH colocalization indexes (p < 0.0001 each). Combining the three biomarkers completely separated the groups. Cluster analysis identified two distinct groups (p < 0.0001) independently of the clinical diagnosis, with one cluster corresponding exactly to LB nOH.

CONCLUSION

LB forms of nOH feature cardiac noradrenergic deficiency, olfactory dysfunction, and increased α-syn-TH colocalization in skin biopsies. Combining the data for these variables efficiently separates LB from non-LB nOH. Independently of the clinical diagnosis, this biomarker triad identifies a pathophysiologically distinct cluster of nOH patients.

Exploring the prevalence of undetected bradyarrhythmia in dementia with Lewy bodies

PURPOSE

To explore the prevalence of undetected bradyarrhythmia in a cohort of people with dementia with Lewy bodies.

METHODS

Thirty participants diagnosed with dementia with Lewy bodies were enrolled from three memory clinics in southern Sweden between May 2021 and November 2022. None had a history of high-grade atrioventricular block or sick sinus syndrome. Each participant underwent orthostatic testing, cardiac [123I]metaiodobenzylguanidine scintigraphy and 24-h ambulatory electrocardiographic monitoring. Concluding bradyarrhythmia diagnosis was obtained until the end of December 2022.

RESULTS

Thirteen participants (46.4%) had bradycardia at rest during orthostatic testing and four had an average heart rate < 60 beats per minute during ambulatory electrocardiographic monitoring. Three participants (10.7%) received a diagnosis of sick sinus syndrome, of whom two received pacemaker implants to manage associated symptoms. None received a diagnosis of second- or third-degree atrioventricular block.

CONCLUSION

This report showed a high prevalence of sick sinus syndrome in a clinical cohort of people with dementia with Lewy bodies. Further research on the causes and consequences of sick sinus syndrome in dementia with Lewy bodies is thus warranted.

Self-organized yolk sac-like organoids allow for scalable generation of multipotent hematopoietic progenitor cells from induced pluripotent stem cells

Although the differentiation of human induced pluripotent stem cells (hiPSCs) into various types of blood cells has been well established, approaches for clinical-scale production of multipotent hematopoietic progenitor cells (HPCs) remain challenging. We found that hiPSCs cocultured with stromal cells as spheroids (hematopoietic spheroids [Hp-spheroids]) can grow in a stirred bioreactor and develop into yolk sac-like organoids without the addition of exogenous factors. Hp-spheroid-induced organoids recapitulated a yolk sac-characteristic cellular complement and structures as well as the functional ability to generate HPCs with lympho-myeloid potential. Moreover, sequential hemato-vascular ontogenesis could also be observed during organoid formation. We demonstrated that organoid-induced HPCs can be differentiated into erythroid cells, macrophages, and T lymphocytes with current maturation protocols. Notably, the Hp-spheroid system can be performed in an autologous and xeno-free manner, thereby improving the feasibility of bulk production of hiPSC-derived HPCs in clinical, therapeutic contexts.

Assessment of myocardial sympathetic innervation with 18F-FDOPA-PET/CT in patients with autonomic dysfunction: feasibility study in IPD patients

BACKGROUND

Dysfunction and denervation of myocardial nor-adrenergic sympathetic neurons has been documented in IPD patients with dysautonomia. The aim of this study was to evaluate the feasibility of single tracer imaging of myocardial sympathetic and cerebral striatal involvement in these patients.

METHODS

Twenty-two controls (mean-age 59.09 ± 12.39 years, 15 men) with no clinical autonomic-dysfunction and normal striatal-uptake in 18F-FDOPA-PET/CT; and 28 patients (mean-age 58.18 ± 8.25 years, 18 men) with autonomic-dysfunction (in Autonomic Function Tests) and striatal dopaminergic-dysfunction were enrolled. Both cardiac-PET/CT (40 minutes post IV-injection of 185-259MBq 18F-FDOPA) and Brain-PET/CT (60 minutes post-IV) were acquired in same session. ROIs were drawn over the entire left ventricular myocardium, individual walls and mediastinum for quantification. Patients and controls were followed-up for 26.93 ± 5.43 months and 37.91 ± 8.63 months, respectively.

RESULTS

Striatal and myocardial-parameters were significantly lower in patients compared to controls; with Myocardium/mediastinal ratio (MwMR) yielding the area-under-the-curve of .941 (P < .001). MwMR correlated negatively with the drop in systolic blood pressure (SBP) during AFTs {Pearson-coefficient (-).565, P = .002}. Mean MwMR in patients with abnormal-AFTs was significantly lower than patients with borderline-AFTs (1.39 ± .12 vs 1.55 ± .10; P = .002). 9/20 patients with abnormal-AFTs showed functional worsening during follow-up, compared to 2/8 with borderline-AFTs.

CONCLUSION

Single tracer, single session imaging of striatal and cardiac sympathetic dysfunction in patients with advanced IPD is feasible with use of 18F-FDOPA. Significantly reduced 18F-FDOPA uptake is seen in the myocardium of the IPD patients with sympathetic dysfunction.

Cardiac Alpha-Synuclein Is Present in Alpha-Synucleinopathies

Background: Alpha-synucleinopathies (AS) are characterized by pathologic aggregations of alpha-synuclein (α-syn) in the central nervous system, and comprise dementia with Lewy bodies, Parkinson’s disease, and multiple system atrophy. Previous studies on AS have reported findings of α-syn pathology in the peripheral nervous system of multiple organs, including the heart. Objective: The aim of this study was to further investigate and confirm the presence of cardiac α-syn in AS compared to other major neurocognitive disorders in a neuropathologically confirmed cohort. Methods: All deceased patients with performed autopsy and with neuropathologically confirmed AS at the Clinical Department of Pathology in Lund 2010–May 2021 were evaluated for inclusion. Cases with insufficiently sampled cardiac tissue or only limited neuropathological investigation were excluded. An age-matched group of individuals with other neurodegenerative diseases, having no α-syn in the CNS, served as controls. In total, 68 AS and 32 control cases were included in the study. Immunohistochemistry for detection of cardiac α-syn aggregates was performed. Results: The AS group had a significantly higher prevalence of cardiac α-syn pathology (p≤0.001) than the control group, 82% and 0%, respectively. Conclusion: This study confirms the association between AS and the presence of cardiac α-syn in a neuropathologically confirmed cohort. This motivates further research on potential pathophysiological effects on cardiac function in AS patients.

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.

Different phenoconversion pathways in pure autonomic failure with versus without Lewy bodies

Pure autonomic failure (PAF) is a rare disease in which chronic neurogenic orthostatic hypotension (nOH) dominates the clinical picture. Longitudinal studies have reported that PAF can phenoconvert to a central synucleinopathy with motor or cognitive involvement-i.e., to Parkinson disease (PD), dementia with Lewy bodies (DLB), or multiple system atrophy (MSA). These studies have classified patients clinically as having PAF based on nOH without an identified secondary cause or clinical evidence of motor or cognitive impairment due to central neurodegeneration. This approach lumps together two nOH syndromes that are pathologically and neurochemically distinct. One is characterized by intraneuronal cytoplasmic alpha-synuclein aggregates (i.e., Lewy bodies) and degeneration of postganglionic sympathetic neurons, as in PD and DLB; the other is not, as in MSA. Clinical and postmortem data show that the form of PAF that involves sympathetic intraneuronal synucleinopathy and noradrenergic deficiency can phenoconvert to PD or DLB-but not to MSA. Conversely, PAF without these features leaves open the possibility of premotor MSA.

α-Synuclein Deposition in Sympathetic Nerve Fibers in Genetic Forms of Parkinson's Disease

BACKGROUND

Cytoplasmic inclusions of α-synuclein (α-syn) in brainstem neurons are characteristic of idiopathic Parkinson's disease (PD). PD also entails α-syn buildup in sympathetic nerves. Among genetic forms of PD, the relative extents of sympathetic intraneuronal accumulation of α-syn have not been reported.

OBJECTIVE

This cross-sectional observational study compared magnitudes of intraneuronal deposition of α-syn in common and rare genetic forms of PD.

METHODS

α-Syn deposition was quantified by the α-syn-tyrosine hydroxylase colocalization index in C2 cervical skin biopsies from 65 subjects. These included 30 subjects with pathogenic mutations in SNCA (n = 3), PRKN [biallelic (n = 7) and monoallelic (n = 3)], LRRK2 (n = 7), GBA (n = 7), or PARK7/DJ1 [biallelic (n = 1) and monoallelic (n = 2)]. Twenty-five of the mutation carriers had PD and five did not. Data were also analyzed from 19 patients with idiopathic PD and 16 control participants.

RESULTS

α-Syn deposition varied as a function of genotype (F = 16.7, P < 0.0001). It was above the control range in 100% of subjects with SNCA mutations, 100% with LRRK2 mutations, 95% with idiopathic PD, 83% with GBA mutations, and 0% with biallelic PRKN mutations. α-Syn deposition in the biallelic PRKN group was significantly higher than in the control group. In addition, patients with biallelic PRKN mutations had higher α-syn deposition than their unaffected siblings.

CONCLUSIONS

Individuals with SNCA, DJ-1, LRRK2, or GBA mutations have substantial intraneuronal α-syn deposition in sympathetic noradrenergic nerves in skin biopsies, whereas those with biallelic PRKN mutations do not. Biallelic PRKN patients may have mildly increased α-syn deposition compared with control subjects. © 2021 International Parkinson and Movement Disorder Society.

The "Sick-but-not-Dead" Phenomenon Applied to Catecholamine Deficiency in Neurodegenerative Diseases

The catecholamines dopamine and norepinephrine are key central neurotransmitters that participate in many neurobehavioral processes and disease states. Norepinephrine is also the main neurotransmitter mediating regulation of the circulation by the sympathetic nervous system. Several neurodegenerative disorders feature catecholamine deficiency. The most common is Parkinson's disease (PD), in which putamen dopamine content is drastically reduced. PD also entails severely decreased myocardial norepinephrine content, a feature that characterizes two other Lewy body diseases-pure autonomic failure and dementia with Lewy bodies. It is widely presumed that tissue catecholamine depletion in these conditions results directly from loss of catecholaminergic neurons; however, as highlighted in this review, there are also important functional abnormalities in extant residual catecholaminergic neurons. We refer to this as the "sick-but-not-dead" phenomenon. The malfunctions include diminished dopamine biosynthesis via tyrosine hydroxylase (TH) and L-aromatic-amino-acid decarboxylase (LAAAD), inefficient vesicular sequestration of cytoplasmic catecholamines, and attenuated neuronal reuptake via cell membrane catecholamine transporters. A unifying explanation for catecholaminergic neurodegeneration is autotoxicity exerted by 3,4-dihydroxyphenylacetaldehyde (DOPAL), an obligate intermediate in cytoplasmic dopamine metabolism. In PD, putamen DOPAL is built up with respect to dopamine, associated with a vesicular storage defect and decreased aldehyde dehydrogenase activity. Probably via spontaneous oxidation, DOPAL potently oligomerizes and forms quinone-protein adducts with ("quinonizes") α-synuclein (AS), a major constituent in Lewy bodies, and DOPAL-induced AS oligomers impede vesicular storage. DOPAL also quinonizes numerous intracellular proteins and inhibits enzymatic activities of TH and LAAAD. Treatments targeting DOPAL formation and oxidation therefore might rescue sick-but-not-dead catecholaminergic neurons in Lewy body diseases.

Cardiac sympathetic innervation and vesicular storage in pure autonomic failure

Objective

Pure autonomic failure (PAF) is a rare disease characterized by neurogenic orthostatic hypotension (nOH), absence of signs of central neurodegeneration, and profound deficiency of the sympathetic neurotransmitter norepinephrine. Reports have disagreed about mechanisms of the noradrenergic lesion. Neuropathological studies have highlighted denervation, while functional studies have emphasized deficient vesicular sequestration of cytoplasmic catecholamines in extant neurons. We examined both aspects by a combined positron emission tomographic (PET) neuroimaging approach using ¹¹C‐methylreboxetine (¹¹C‐MRB), a selective ligand for the cell membrane norepinephrine transporter, to quantify interventricular septal myocardial noradrenergic innervation and using ¹⁸F‐dopamine (¹⁸F‐DA) to assess intraneuronal vesicular storage in the same subjects.

Methods

Seven comprehensively tested PAF patients and 11 controls underwent ¹¹C‐MRB PET scanning for 45 minutes (dynamic 5X1’, 3X5’, 1X10’, static 15 minutes) and ¹⁸F‐DA scanning for 30 minutes (same dynamic imaging sequence) after 3‐minute infusions of the tracers on separate days.

Results

In the PAF group septal ¹¹C‐MRB‐derived radioactivity in the static frame was decreased by 26.7% from control (p = 0.012). After adjustment for nonspecific binding of ¹¹C‐MRB, the PAF group had a 41.1% mean decrease in myocardial ¹¹C‐MRB‐derived radioactivity (p = 0.015). The PAF patients had five times faster postinfusion loss of ¹⁸F‐DA‐derived radioactivity (70 ± 3% vs. 14 ± 8% by 30 minutes, p < 0.0001). At all time points after infusion of ¹⁸F‐DA and ¹¹C‐MRB mean ¹⁸F/¹¹C ratios in septal myocardium were lower in the PAF than control group.

Interpretation

PAF entails moderately decreased cardiac sympathetic innervation and a substantial vesicular storage defect in residual nerves.

Association of innervation-adjusted alpha-synuclein in arrector pili muscles with cardiac noradrenergic deficiency in autonomic synucleinopathies

BACKGROUND

Autonomic synucleinopathies feature deposition of the protein alpha-synuclein (AS) in neurons [e.g., Lewy body neurogenic orthostatic hypotension (nOH)] or glial cells (multiple system atrophy, MSA). AS in skin biopsies might provide biomarkers of these diseases; however, this approach would be complicated or invalidated if there were substantial loss of AS-containing nerves. We report AS content in arrector pili muscles in skin biopsies after adjustment for local innervation in patients with Lewy body nOH or MSA. Cardiac sympathetic neuroimaging by myocardial ¹⁸F-dopamine positron emission tomography (PET) was done to examine pathophysiological correlates of innervation-adjusted AS.

METHODS

Thirty-one patients (19 Lewy body nOH, 12 MSA) underwent thoracic ¹⁸F-dopamine PET and skin biopsies. AS signal intensity analyzed by immunofluorescence microscopy was adjusted for innervation by the ratio of AS to protein gene product (PGP) 9.5, a pan-axonal marker (Harvard lab site), or the ratio of AS to tyrosine hydroxylase (TH), an indicator of catecholaminergic neurons (NIH lab site).

RESULTS

The Lewy body nOH group had higher ratios of AS/PGP 9.5 or log AS/TH than did the MSA group (0.89 ± 0.05 vs. 0.66 ± 0.04, -0.13 ± 0.05 vs. -1.60 ± 0.33; p < 0.00001 each). All 19 Lewy body patients had AS/PGP 9.5 > 0.8 or log AS/TH > 1.2 and had myocardial ¹⁸F-dopamine-derived radioactivity < 6000 nCi-kg/cc-mCi, the lower limit of normal. Two MSA patients (17%) had increased AS/PGP or log AS/TH, and two (17%) had low ¹⁸F-dopamine-derived radioactivity.

CONCLUSIONS

Lewy body forms of nOH are associated with increased innervation-adjusted AS in arrector pili muscles and neuroimaging evidence of myocardial noradrenergic deficiency.

Computational modeling reveals multiple abnormalities of myocardial noradrenergic function in Lewy body diseases

BACKGROUND

Lewy body diseases, a family of aging-related neurodegenerative disorders, entail loss of the catecholamine dopamine in the nigrostriatal system and equally severe deficiency of the closely related catecholamine norepinephrine in the heart. The myocardial noradrenergic lesion is associated with major non-motor symptoms and decreased survival. Numerous mechanisms determine norepinephrine stores, and which of these are altered in Lewy body diseases has not been examined in an integrated way. We used a computational modeling approach to assess comprehensively pathways of cardiac norepinephrine synthesis, storage, release, reuptake, and metabolism in Lewy body diseases. Application of a novel kinetic model identified a pattern of dysfunctional steps contributing to norepinephrine deficiency. We then tested predictions from the model in a new cohort of Parkinson disease patients.

METHODS

Rate constants were calculated for 17 reactions determining intra-neuronal norepinephrine stores. Model predictions were tested by measuring post-mortem apical ventricular concentrations and concentration ratios of catechols in controls and patients with Parkinson disease.

RESULTS

The model identified low rate constants for three types of processes in the Lewy body group-catecholamine biosynthesis via tyrosine hydroxylase and L-aromatic-amino-acid decarboxylase, vesicular storage of dopamine and norepinephrine, and neuronal norepinephrine reuptake via the cell membrane norepinephrine transporter. Post-mortem catechols and catechol ratios confirmed this triad of model-predicted functional abnormalities.

CONCLUSION

Denervation-independent impairments of neurotransmitter biosynthesis, vesicular sequestration, and norepinephrine recycling contribute to the myocardial norepinephrine deficiency attending Lewy body diseases. A proportion of cardiac sympathetic nerves are "sick but not dead," suggesting targeted disease-modification strategies might retard clinical progression.

TRIAL REGISTRATION

This study was not a clinical trial.

FUNDING

The research reported here was supported by the Division of Intramural Research, NINDS.

Alpha-Synuclein Deposition Within Sympathetic Noradrenergic Neurons Is Associated With Myocardial Noradrenergic Deficiency in Neurogenic Orthostatic Hypotension

Lewy body diseases involve neurogenic orthostatic hypotension (nOH), cardiac noradrenergic deficiency, and deposition of the protein AS (alpha-synuclein) in sympathetic ganglion tissue. Mechanisms linking these abnormalities are poorly understood. One link may be AS deposition within sympathetic neurons. We validated methodology to quantify AS colocalization with TH (tyrosine hydroxylase), a marker of sympathetic noradrenergic innervation, and assessed associations of AS/TH colocalization with myocardial norepinephrine content and cardiac sympathetic neuroimaging data in nOH. Postmortem sympathetic ganglionic AS/TH colocalization indices and myocardial norepinephrine contents were measured in 4 Lewy body and 3 rare non-Lewy body nOH patients. Sixteen Lewy body and 11 non-Lewy body nOH patients underwent in vivo skin biopsies and thoracic 18F-dopamine positron emission tomographic scanning, with cutaneous colocalization indices expressed versus cardiac 18F-dopamine-derived radioactivity. Ganglionic AS/TH colocalization indices were higher and myocardial norepinephrine lower in Lewy body than non-Lewy body nOH ( P=0.0020, P=0.014). The Lewy body nOH group had higher AS/TH colocalization indices in skin biopsies and lower myocardial 18F-dopamine-derived radioactivity than did the non-Lewy body nOH group ( P<0.0001 each). All Lewy body nOH patients had colocalization indices >1.5 in skin biopsies and 18F-dopamine-derived radioactivity <6000 nCi-kg/cc-mCi, a combination not seen in non-Lewy body nOH patients ( P<0.0001). In Lewy body nOH, AS deposition in sympathetic noradrenergic nerves is related to postmortem neurochemical and in vivo neuroimaging evidence of myocardial noradrenergic deficiency. These associations raise the possibility that intraneuronal AS deposition plays a pathophysiological role in the myocardial sympathetic neurodegeneration attending Lewy body nOH.

Orthostatic heart rate changes in patients with autonomic failure caused by neurodegenerative synucleinopathies

OBJECTIVE

Blunted tachycardia during hypotension is a characteristic feature of patients with autonomic failure, but the range has not been defined. This study reports the range of orthostatic heart rate (HR) changes in patients with autonomic failure caused by neurodegenerative synucleinopathies.

METHODS

Patients evaluated at sites of the U.S. Autonomic Consortium (NCT01799915) underwent standardized autonomic function tests and full neurological evaluation.

RESULTS

We identified 402 patients with orthostatic hypotension (OH) who had normal sinus rhythm. Of these, 378 had impaired sympathetic activation (ie, neurogenic OH) and based on their neurological examination were diagnosed with Parkinson disease, dementia with Lewy bodies, pure autonomic failure, or multiple system atrophy. The remaining 24 patients had preserved sympathetic activation and their OH was classified as nonneurogenic, due to volume depletion, anemia, or polypharmacy. Patients with neurogenic OH had twice the fall in systolic blood pressure (SBP; -44 ± 25 vs -21 ± 14 mmHg [mean ± standard deviation], p < 0.0001) but only one-third of the increase in HR of those with nonneurogenic OH (8 ± 8 vs 25 ± 11 beats per minute [bpm], p < 0.0001). A ΔHR/ΔSBP ratio of 0.492 bpm/mmHg had excellent sensitivity (91.3%) and specificity (88.4%) to distinguish between patients with neurogenic from nonneurogenic OH (area under the curve = 0.96, p < 0.0001). Within patients with neurogenic OH, HR increased more in those with multiple system atrophy (p = 0.0003), but there was considerable overlap with patients with Lewy body disorders.

INTERPRETATION

A blunted HR increase during hypotension suggests a neurogenic cause. A ΔHR/ΔSBP ratio < 0.5 bpm/mmHg is diagnostic of neurogenic OH. Ann Neurol 2018;83:522-531.