
==== Front
Eur J Neurol
Eur J Neurol
10.1111/(ISSN)1468-1331
ENE
European Journal of Neurology
1351-5101
1468-1331
John Wiley and Sons Inc. Hoboken

38946703
10.1111/ene.16388
ENE16388
EJoN-24-0515.R1
Original Article
Dementia and Cognitive Disorders
Association of elevated cerebrospinal fluid levels of the longevity protein α‐Klotho with a delayed onset of cognitive impairment in Parkinson's disease patients
Levels of α‐Klotho in CSF as modifier in Parkinson's disease
Zimmermann et al.
Zimmermann Milan 1 2 milan.zimmermann@uni-tuebingen.de

Fandrich Madeleine 3
Jakobi Meike 3
Röben Benjamin https://orcid.org/0000-0002-4905-8698
1 2
Wurster Isabel https://orcid.org/0000-0003-0157-5722
1 2
Lerche Stefanie 1 2
Schulte Claudia 1 2
Zimmermann Shahrzad 1
Deuschle Christian 1 2
Schneiderhan‐Marra Nicole 3
Gasser Thomas 1 2
Brockmann Kathrin 1 2
1 Center of Neurology Department of Neurodegeneration and Hertie‐Institute for Clinical Brain Research University of Tuebingen Germany
2 German Center for Neurodegenerative Diseases (DZNE) University of Tuebingen Germany
3 Natural and Medical Sciences Institute University of Tuebingen Reutlingen Germany
* Correspondence
Milan Zimmermann, Department of Neurodegeneration, Hertie Institute for Clinical Brain Research, University of Tuebingen, Hoppe Seyler‐Strasse 3, 72076 Tuebingen, Germany.
Email: milan.zimmermann@uni-tuebingen.de

01 7 2024
10 2024
31 10 10.1111/ene.v31.10 e1638805 6 2024
14 3 2024
06 6 2024
© 2024 The Author(s). European Journal of Neurology published by John Wiley & Sons Ltd on behalf of European Academy of Neurology.
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Abstract

Background and Purpose

Parkinson's disease (PD) is an age‐related condition characterized by substantial phenotypic variability. Consequently, pathways and proteins involved in biological aging, such as the central aging pathway comprising insulin‐like growth factor 1–α‐Klotho–sirtuin 1–forkhead box O3–peroxisome proliferator‐activated receptor γ, may potentially influence disease progression.

Methods

Cerebrospinal fluid (CSF) levels of α‐Klotho in 471 PD patients were examined. Of the 471 patients, 96 carried a GBA1 variant (PD GBA1), whilst the 375 non‐carriers were classified as PD wild‐type (PD WT). Each patient was stratified into a CSF α‐Klotho tertile group based on the individual level. Kaplan–Meier survival curves and Cox regression analysis stratified by tertile groups were conducted. These longitudinal data were available for 255 patients. Follow‐up times reached from 8.4 to 12.4 years. The stratification into PD WT and PD GBA1 was undertaken to evaluate potential continuum patterns, particularly in relation to CSF levels.

Results

Higher CSF levels of α‐Klotho were associated with a significant later onset of cognitive impairment. Elevated levels of α‐Klotho in CSF were linked to higher Montreal Cognitive Assessment scores in male PD patients with GBA1 mutations.

Conclusions

Our results indicate that higher CSF levels of α‐Klotho are associated with a delayed cognitive decline in PD. Notably, this correlation is more prominently observed in PD patients with GBA1 mutations, potentially reflecting the accelerated biological aging profile characteristic of individuals harboring GBA1 variants.

High CSF levels of alpha‐Klotho were associated with a later onset of cognitive impairment in patients with Parkinson´s disease.

aging
neurodegeneration
neurodegenerative diseases
Parkinson's disease
α‐Klotho
Ministerium für Wirtschaft, Arbeit und Wohnungsbau Baden‐Württemberg 10.13039/501100011736 FKZ AZ 35‐4223.10/8 source-schema-version-number2.0
cover-dateOctober 2024
details-of-publishers-convertorConverter:WILEY_ML3GV2_TO_JATSPMC version:6.4.8 mode:remove_FC converted:20.09.2024
Zimmermann M , Fandrich M , Jakobi M , et al. Association of elevated cerebrospinal fluid levels of the longevity protein α‐Klotho with a delayed onset of cognitive impairment in Parkinson's disease patients. Eur J Neurol. 2024;31 :e16388. doi:10.1111/ene.16388
==== Body
pmcINTRODUCTION

Parkinson's disease (PD) is an age‐related disorder. Incidence increases with age, highlighting age as one of the strongest risk factors for PD [1]. Moreover, it is well known from community‐based longitudinal cohorts that chronological age and older age at onset independently predict cognitive decline, motor worsening and mortality in PD [2, 3, 4]. The phenotypic variability with regard to the manifestation of motor and nonmotor symptoms and disease milestones such as cognitive impairment might be partly due to disease‐modifying factors such as lifestyle and genetic variation with corresponding protein profiles [5, 6].

In this line, the central aging pathway insulin‐like growth factor 1 (IGF1)–α‐Klotho–sirtuin 1 (SIRT1)–forkhead box O3 (FOXO3a)–peroxisome proliferator‐activated receptor γ (PPARγ) is a promising target for biomarker research. α‐Klotho knockout mice show a phenotype of premature aging with arteriosclerosis, osteoporosis, muscle atrophy, neuronal degeneration, a short lifespan and infertility [7, 8]. Mice with α‐Klotho deficiency specifically exhibit nigrostriatal dopaminergic degeneration, providing a link between pathological aging processes and PD‐associated neurodegeneration [9, 10]. α‐Klotho is a transmembrane protein which constitutes also a soluble form that is highly expressed in the brain [11, 12] and acts as a coreceptor for fibroblast growth factor 23 (FGF23) [13]. α‐Klotho stimulates the transcription factor FOXO3a [14], leading to increased expression of superoxide dismutase and human catalase via activation of PPARγ, amongst others, through phosphoinositide 3‐kinase/protein kinase B (PI3K/AKT) pathway inhibition [14]. Thus, it prevents the hyperphosphorylation of FOXO3a and its dislocation from the nucleus [15] (Figure 1). PD research in vitro and in mouse models has shown that activation of PPARγ via an agonist (pioglitazone) results in reduction of reactive oxygen species (ROS) [17, 18], a decrease in neuroinflammation by reduced levels of interleukins, tumor necrosis factor α and major histocompatibility complex, accompanied by mitochondrial biogenesis and increased autophagy [19, 20].

FIGURE 1 α‐Klotho counteracts the phosphorylation of Forkhead box O3 (FOXO3a), amongst others, via phosphoinositide 3‐kinase/protein kinase B (PI3K/AKT) inhibition, preventing the dislocation of this central transcription factor from the nucleus and thus leading to increased expression of antioxidative enzymes like superoxide dismutase II (SODII) and human catalase (CAT) via activation of peroxisome proliferator‐activated receptor γ (PPARγ). Possible effects are a lower production of interleukins and reactive oxygen species, an increase in mitochondrial biogenesis and autophagy and thus an increase in life expectancy [16]. Created with BioRender.com.

In this line of reasoning, the aim was to address the question whether alterations in concentrations of cerebrospinal fluid (CSF) α‐Klotho predispose toward a more rapid progression of cognitive impairment longitudinally in a large cohort of PD patients including also a considerable subgroup with glucocerebrosidase 1 (GBA1) variants as proxy for an accelerated progression [21].

METHODS

Participants and clinical investigations

All 471 PD patients (referred to as the PD total cohort) were recruited and examined between 2001 and 2022 from the ward and outpatient clinic for Parkinson's disease at the University of Tuebingen. All patients were examined by a movement disorder specialist. The diagnosis of PD was defined according to UK Brain Bank criteria [22]. The following demographic and clinical data were obtained: age, sex, age at onset of parkinsonism. Additionally, the disease duration was calculated. The severity of motor symptoms was assessed using the Unified Parkinson's Disease Rating Scale part III (UPDRS III) from 2000 to 2008, and from 2009 the Movement Disorder Society (MDS) UPDRS was applied [23]. Cognitive function was tested using the Montreal Cognitive Assessment (MoCA) [24] or the Mini Mental State Examination (MMSE) [25]. As the MoCA has only been available since 2009, all MMSE scores were converted to MoCA equivalent scores according to an algorithm published recently [26]. An MoCA cutoff ≤25 indicated cognitive impairment (point of maximum combined sensitivity and specificity [27]). Depressive symptoms were assessed using Beck's Depression Inventory (BDI) II [28]. The PD cohort, subjected to α‐Klotho measurements, was chosen based on the criterion of possessing a comprehensive clinical dataset. Of the 471 PD patients, 255 had longitudinal data pertaining to the onset of cognitive impairment, forming the smaller longitudinal sub‐cohort.

Analysis of α‐Klotho CSF protein profiles

A commercial enzyme‐linked immunosorbent assay kit (IBL International, Hamburg, Germany, Cat# 27998, LOT# 2C‐117) was used for the detection of α‐Klotho (in ng/mL). Single analyses were performed of 1:2 diluted samples. The assay was performed according to the manufacturer's protocol. Briefly, 100 μL of either standards or samples or quality control samples are pipetted into the wells of a 96‐well plate coated with capture antibody. α‐Klotho was allowed to bind for 1 h at room temperature. Unbound sample was removed, and wells were washed four times with wash buffer. 100 μL detection antibody was added to each well and incubated for 30 min before removal of unbound detection antibody and washing steps. 100 μL tetramethylbenzidine substrate solution was added to each well. After further incubation for 30 min, 100 μL stop solution was added to the wells. Optical density was determined using an Biotek ELX808 at 450 nm (main wavelength) to 630 nm (sub‐wavelength). Concentrations were back calculated using a 5PL regression fit on the standard samples (Biotek ELX808).

Statistics

Statistical analysis was performed using IBM SPSS Statistics (IBM Corp., released 2021, IBM SPSS Statistics for Macintosh, Version 28.0. Armonk, NY, USA).

Analysis of covariance (ANCOVA), with covariates sex, age at examination and disease duration, was applied to compare demographic and clinical data along with CSF levels of α‐Klotho between PD WT and PD GBA1, for the comparison of GBA1 variants (mild, risk, severe), for comparing α‐Klotho levels between males and females in the PD total cohort, PD WT and PD GBA1 and for the comparison of follow‐up times depending on the α‐Klotho tertile levels in the PD total cohort and PD WT. Given the limited number of patients in PD GBA1, the non‐parametric Mann–Whitney U test was conducted to compare follow‐up times and age at examination in this sub‐cohort.

Pearson correlation analysis was employed to investigate the influence of α‐Klotho levels and age at examination on demographic, clinical and biomarker data. η 2 was calculated to assess the impact of sex on α‐Klotho levels (Table S1).

Categorical variables (such as the incidence of cognitive impairment during the study period or prevalence of severe GBA1 variants) were compared using the χ 2 test.

Kaplan–Meier curves, along with Cox regression analysis incorporating the factor “tertile group”, were employed for longitudinal analysis regarding the onset of cognitive impairment. For these analyses, the lowest versus mid versus highest tertile of CSF α‐Klotho levels were compared (Figure 2 and Table S2).

FIGURE 2 Kaplan–Meier survival curves and Cox regression analysis for the time interval (in years) until 50% of the Parkinson's disease patients reached the milestone cognitive impairment (MoCA ≤25) in the PD total cohort (a), the PD wild‐type (WT) (b) and PD GBA1 (c), stratified by tertiles of CSF α‐Klotho levels. Categories: lowest tertile of α‐Klotho CSF levels; mid tertile of α‐Klotho levels; highest tertile of α‐Klotho levels. p values <0.05 are highlighted in bold.

RESULTS

Demographic and cross‐sectional data

PD total cohort

Of the 471 PD patients, 308 were male (65.4%). The age at examination was 65.4 years (± 9.9), the age at onset 58.1 years (± 10.5), the disease duration 7.3 years (± 5.1), the MoCA score 25.3 (± 3.9), the UPDRS III score 26.0 (± 11.5) and the BDI II score 9.1 (± 7.1) (Table 1).

TABLE 1 Demographic, clinical and cerebrospinal fluid (CSF) biomarker data in patients diagnosed with Parkinson's disease (PD): analysis of the total cohort, PD wild‐type (WT) and PD GBA1 subgroups.

	Cross‐sectional cohort	Longitudinal cohort	
PD total	PD WT	PD GBA1	PD total	PD WT	PD GBA1	
Age at examination	65.4 (± 9.9)	65.9 (± 9.9)	63.4 (± 9.4) §	62.2 (± 9.6)	62.6 (± 9.5)	60.8 (± 9.8)	
N = 471	N = 375	N = 96	N = 255	N = 198	N = 57	
Age at onset	58.1 (± 10.5)	58.9 (± 10.4)	55.1 (± 10.2) §§	55.5 (± 10.1)	56.1 (±  9.7)	53.5 (±  11.3)	
N = 471	N = 375	N = 96	N = 255	N = 198	N = 57	
Disease duration	7.3 (± 5.1)	7.1 (± 4.9)	8.3 (± 5.6) §	6.7 (± 5.0)	6.5 (± 4.8)	7.3 (± 5.7)	
N = 471	N = 375	N = 96	N = 255	N = 198	N = 57	
UPDRS III	26.0 (± 11.5)	25.9 (± 11.4)	26.6 (± 11.7)	24.8 (± 11.3)	24.8 (± 11.8)	24.7 (± 9.8)	
N = 442	N = 350	N = 92	N = 250	N = 193	N = 57	
MoCA	25.3 (± 3.9)	25.4 (± 3.6)	24.8 (± 4.8) §	27.3 (± 2.3)	27.3 (± 2.2)	27.2 (± 2.5)	
N = 403	N = 315	N = 88	N = 242	N = 187	N = 55	
BDI II	9.1 (± 7.1)	8.8 (± 7.0)	10.2 (± 7.3)	8.2 (± 6.5)	8.0 (± 6.6)	8.8 (± 6.3)	
N = 347	N = 274	N = 73	N = 203	N = 158	N = 45	
β‐amyloid 1–42 (in pg/mL)	722.7 (± 269.5)	720.2 (± 268.9)	732.2 (± 272.9)	720.8 (± 242.8)	707.4 (± 229.5)	767.1 (± 281.4)	
N = 449	N = 356	N = 93	N = 245	N = 190	N = 55	
h‐tau (in pg/mL)	250.3 (± 130.9)	250.7 (± 130.1)	248.8 (± 134.7)	232.4 (± 105.1)	232.6 (± 111.7)	232.0 (± 79.0)	
N = 449	N = 356	N = 93	N = 245	N = 190	N = 55	
p‐tau (in pg/mL)	42.2 (± 17.0)	42.7 (± 17.0)	40.6 (± 16.8)	40.4 (± 15.9)	40.4 (± 16.0)	40.8 (± 15.4)	
N = 440	N = 349	N = 91	N = 241	N = 186	N = 55	
NfL (in pg/mL)	971.2 (± 801.7)	986.2 (± 846.2)	914.6 (± 605.6)	878.6 (± 906.5)	886.9 (± 978.6)	850.9 (± 612.5)	
N = 430	N = 340	N = 90	N = 239	N = 184	N = 55	
α‐synuclein (in pg/mL)	614.3 (± 299.0)	631.4 (± 307.7)	545.2 (± 250.9) §	602.4 (± 301.8)	613.5 (± 314.6)	562.1 (± 248.3)	
N = 444	N = 356	N = 88	N = 241	N = 189	N = 52	
α‐Klotho (in ng/mL)	1.12 (± 0.43)	1.12 (± 0.42)	1.11 (± 0.47)	1.16 (± 0.44)	1.15 (± 0.40)	1.18 (± 0.56)	
N = 471	N = 375	N = 96	N = 255	N = 198	N = 57	
Note: Data are presented for the cross‐sectional cohort and the smaller longitudinal sub‐cohort, including patients with Kaplan–Meier data. Analysis of covariance (ANCOVA) with covariates age at examination, disease duration and sex with significant p values <0.05 presented as follows: “§” indicates the comparison between PD WT and PD GBA1; the levels of significance are indicated as follows: 0.001 < p ≤ 0.01: §§; 0.01 < p < 0.05: §.

Abbreviations: BDI II, Beck's Depression Inventory II; GBA1, variant in the gene glucocerebrosidase 1; MoCA, Montreal Cognitive Assessment; NfL, neurofilament light chain; UPDRS III, Unified Parkinson's Disease Rating Scale part III; WT, wild‐type.

Lower CSF levels of α‐Klotho were associated with a higher age at examination (−0.098, N = 471, p = 0.033) and a higher age at onset (−0.092, N = 471, p = 0.046). Additional correlations between α‐Klotho and demographic, clinical and biomarker data did not attain statistical significance (Table S1).

No significant differences were found between male and female PD patients regarding α‐Klotho levels (male 1.13 (± 0.46), N = 308; female 1.09 (± 0.38), N = 163; p = 0.412).

PD WT

In PD WT, 244 out of 375 patients were male (65.1%). The age at examination was 65.9 years (± 9.9), the age at onset 58.9 years (± 10.4), the disease duration 7.1 years (± 4.9), the MoCA score 25.4 (± 3.6), the UPDRS III score 25.9 (± 11.4) and the BDI II score 8.8 (± 7.0) (Table 1).

Lower CSF levels of α‐Klotho were associated with a higher age at examination (−0.134, N = 375, p = 0.009) and a higher age at onset (−0.125, N = 375, p = 0.015). Other correlations did not achieve statistical significance (Table S1).

No significant differences were found between male and female PD patients regarding α‐Klotho levels (male 1.13 (± 0.45), N = 244; female 1.09 (± 0.36), N = 131; p = 0.452).

PD GBA1

In total, 96 patients of the total cohort had a genetic variant in the gene GBA1 (PD GBA1). 64 out of 96 patients were male (66.7%). The age at examination was 63.4 years (± 9.4), the age at onset 55.1 years (± 10.2), the disease duration 8.3 years (± 5.6), the MoCA score 24.8 (± 4.8), the UPDRS III score 26.6 (± 11.7) and the BDI II score 10.2 (± 7.3) (Table 1).

Correlations between α‐Klotho levels and age at examination did not reach statistical significance (0.026, N = 96, p = 0.803). In male PD GBA1 patients, higher CSF α‐Klotho levels were associated with higher MoCA scores (r = 0.257, N = 59, p = 0.050). Other correlations did not achieve statistical significance (Table S1).

No significant differences were observed between male and female PD GBA1 patients in terms of α‐Klotho levels (male 1.12 (± 0.49), N = 64; female 1.08 (± 0.45), N = 32; p = 0.647). Similarly, there were no significant differences observed between PD WT and PD GBA1 (1.12 (± 0.42) vs. 1.11 (± 0.47), p = 0.682), nor in the comparison between different GBA1 variants (mild 1.29 (± 0.71), N = 20; risk 1.09 (± 0.37), N = 48; severe 1.01 (± 0.40), N = 28; p = 0.141).

Longitudinal analysis

Higher α‐Klotho levels are associated with a significant later onset of cognitive impairment

PD total cohort

The follow‐up time (in years) did not exhibit statistically significant differences amongst the three tertiles of CSF α‐Klotho levels in the sub‐cohort of patients who had Kaplan–Meier data (lowest tertile 8.6 (± 4.8), N = 85; mid tertile 9.2 (± 5.1), N = 85; highest tertile 9.7 (± 6.7), N = 85; p = 0.633). A lower age at examination was found in those patients with the highest tertile of CSF α‐Klotho levels (lowest tertile 63.3 (± 9.7), mid tertile 63.3 (± 8.9), highest tertile 60.0 (± 9.8), p = 0.041).

PD patients exhibiting the highest levels of α‐Klotho demonstrated a reduced incidence of cognitive impairment throughout the study period compared to those with lower CSF levels (lowest tertile 42/85 (49.4%), mid tertile 37/85 (43.5%), highest tertile 26/85 (30.6%), p = 0.039).

The temporal duration (measured in years) until 50% of patients reached cognitive impairment significantly varied amongst the three tertiles of CSF α‐Klotho levels. PD patients within the highest tertile of α‐Klotho levels experienced cognitive impairment at a later stage compared to those in the lowest tertile (lowest tertile 12.3, 95% confidence interval [CI] 10.4–14.3; mid tertile 15.3, 95% CI 12.8–17.7; highest tertile 21.7, 95% CI 15.5–28.0; N = 85, p = 0.009) (Figure 2 and Table S2).

PD WT

The follow‐up time (in years) did not demonstrate statistically significant differences amongst the three tertiles of CSF α‐Klotho levels in the longitudinal sub‐cohort (lowest tertile 8.7 (± 5.1), N = 66; mid tertile 9.6 (± 4.8), N = 66; highest tertile 8.8 (± 6.2), N = 66; p = 0.620). A lower age at examination was found in patients with the highest tertile of α‐Klotho levels compared to those patients with lower levels (lowest tertile 64.2 (± 9.2), mid tertile 63.9 (± 8.9), highest tertile 59.7 (± 9.8), p = 0.008).

Throughout the follow‐up times, PD patients with the highest levels of α‐Klotho presented with a lower incidence of cognitive impairment compared to those patients with lower CSF levels (lowest tertile 30/66 (45.5%), mid tertile 31/66 (47.0%), highest tertile 18/66 (27.3%), p = 0.037).

No statistically significant differences were observed in the time interval until 50% of patients reached cognitive impairment based on the α‐Klotho CSF tertiles (Figure 2 and Table S2).

PD GBA1

The follow‐up time (in years) did not exhibit statistically significant differences amongst the three tertiles of CSF α‐Klotho levels in the longitudinal sub‐cohort (lowest tertile 8.4 (± 3.9), N = 19; mid tertile 9.5 (± 6.6), N = 21; highest tertile 12.1 (± 7.8), N = 17; p = 0.487). Furthermore, no significant differences were found regarding the age at examination in this cohort (lowest tertile 60.2 (± 10.7), mid tertile 61.6 (± 9.0), highest tertile 60.5 (± 10.2), p = 0.858) and regarding the prevalence of severe GBA1 variants (lowest tertile 7/19 (36.8%), mid tertile 5/21 (23.8%), highest tertile 5/17 (29.4%), p = 0.641).

The time interval until 50% of patients reached cognitive impairment differed significantly amongst the three tertiles of CSF α‐Klotho levels. Specifically, in the lowest tertile it was 10.1 years (7.7–12.5), in the mid tertile it was 17.4 years (11.4–23.4) and in the highest tertile it was 20.1 years (13.4–26.8) (p = 0.018) (Figure 2 and Table S2).

Furthermore, PD GBA1 patients with higher levels of α‐Klotho presented with a lower incidence of cognitive impairment during study time (lowest tertile 13/19 (68.4%), mid tertile 7/21 (33.3%), highest tertile 6/17 (35.3%), p = 0.050).

DISCUSSION

Our findings provide evidence for a neuroprotective role of α‐Klotho in patients with PD, based on longitudinal data. High CSF levels of α‐Klotho were associated with a later onset of cognitive impairment. The observed effect within the PD total cohort was evidently primarily attributed to the PD GBA1 sub‐cohort. Given that there were no significant age differences amongst the three tertiles and no significant differences in terms of follow‐up times in PD GBA1, it is highly likely that the observed effect is a consequence of accelerated biological aging signature in patients with GBA1 variants in the lowest CSF α‐Klotho tertile. On the other hand, in the PD total cohort, patients with the highest α‐Klotho levels were younger at the time of examination. This age effect probably contributes to the later onset of cognitive impairment observed in this group. In this context, CSF measurements of α‐Klotho levels might serve as a surrogate marker, mirroring aging processes.

Individuals exhibiting the highest α‐Klotho levels also demonstrated a reduced incidence of cognitive impairment throughout the study duration. Furthermore, elevated levels of α‐Klotho in CSF were linked to higher MoCA scores in male PD patients with GBA1 mutations. As no negative correlation between α‐Klotho and age at examination was observed in PD GBA1, it is unlikely that this association can be attributed to age‐related effects.

The shift from predominant glucose metabolism in the IGF1–α‐Klotho–SIRT1–FOXO3a–PPARγ aging pathway to predominant lipid oxidation via activation of PPARγ appears to be a key pathway in aging processes and in neurodegeneration. This transition is concomitant with the upregulation of enzymes accountable for the detoxification of ROS, generated in greater quantities during lipid metabolism. Furthermore, it fosters mitochondrial biogenesis, resulting in the generation of more “efficient” mitochondria that produce reduced ROS, suppress inflammation [16] and stimulate autophagy. A similar effect can be induced by caloric restriction, which has been shown to be associated with an increase in life expectancy [29]. The potential positive effects on longevity and disease severity in neurodegenerative disorders may be ascribed to a plausible overshooting phenomenon arising from an elevated expression of antioxidative metabolites surpassing the heightened production of ROS. In our study, an advanced age at examination correlated with diminished CSF α‐Klotho levels, suggesting a potentially reduced protective effect against the onset of age‐related diseases such as PD or Alzheimer's disease. In this line, lower CSF levels of α‐Klotho and its corresponding coreceptor FGF23 were found in patients with PD in comparison to controls in a previous study [30]. Our current analyses in an extended cohort substantiate those previous findings suggesting protective strains of high α‐Klotho levels also in a longitudinal perspective, possibly providing further approaches for pharmacological interventions. Notably, polyamine metabolism pathways that influence SIRT1 [31] or PPARγ [32] emerge as particularly promising drug targets in individuals affected by neurodegenerative diseases. Other studies have also investigated the neuroprotective role of α‐Klotho in patients with PD [33]. In this context, CSF levels of α‐Klotho were found to be increased in patients with early‐stage PD. Additionally, the CSF levels of α‐Klotho were inversely correlated with α‐synuclein levels [34].

A limitation of our current study is the use of both the UPDRS III and, since 2009, the MDS‐UPDRS III, which has a broader scale.

If validated in other cohorts, one might envision several beneficial scenarios: (i) patient cohorts might be stratified based on their biological aging footprint in future observational studies and trials; (ii) the IGF1–α‐Klotho–SIRT1–FOXO3a–PPARγ aging pathway might be further studied and potentially targeted by treatments.

AUTHOR CONTRIBUTIONS

Milan Zimmermann, Kathrin Brockmann and Nicole Schneiderhan‐Marra designed the study. Milan Zimmermann, Kathrin Brockmann, Benjamin Röben, Isabel Wurster, Claudia Schulte, Christian Deuschle, Stefanie Lerche and Thomas Gasser generated and collected clinical data. Madeleine Fandrich, Meike Jakobi and Nicole Schneiderhan‐Marra measured the tissue factor levels and Claudia Schulte, Milan Zimmermann, Kathrin Brockmann and Shahrzad Zimmermann performed the statistical analysis. Milan Zimmermann and Kathrin Brockmann drafted the manuscript. All authors were involved in interpretation of the data and critical revision of the manuscript. All authors gave their final approval.

FUNDING INFORMATION

This work was funded by the State Ministry of Baden‐Württemberg for Economic Affairs, Labour and Tourism (Predictive Diagnostic of Immune‐associated Diseases for Personalized Medicine, AZ 35‐4223.10/8). The funder played no role in study design, data collection, analysis and interpretation of data, or the writing of this manuscript.

CONFLICT OF INTEREST STATEMENT

No conflicts of interest are reported for any of the authors in relation to the content of this paper. Dr Kathrin Brockmann received Research Grants from the Michael J. Fox Foundation for Parkinson's Research (LRRK2 Kinase Activity, Influence of Inflammatory Profiles on PD Phenotype and Progression, Prevent Dementia in GBA1‐associated PD), from the University of Tuebingen (Endophenotyping of GBA1‐PD), from the German Society for Parkinson DPG, from the Health Forum Baden Wuerttemberg (Predictive Diagnostic of Immune‐associated Diseases for Personalized Medicine, AZ 35‐4223.10/8), from the Else Kröner Fresenius Stiftung (ClinBrain) and from the German Research Foundation DFG (CORO‐TREND). She serves on advisory boards for F. Hoffmann‐La Roche Ltd and VanqaBio. She received speaker honoraria from Abbvie, Lundbeck, UCB and Zambon. Professor Dr Thomas Gasser serves on the editorial board of the Journal of Parkinson's Disease. He holds a patent re KASPP (LRRK2) gene, its production and use for the detection and treatment of neurodegenerative diseases. Professor Gasser has received speaker's honoraria from UCB Pharma, Novartis, Sanofi and MedUpdate. He has received consulting fees from Bayer AG, BlueRock Therapeutics and Biogen. He is Chairman of the Scientific Advisory Board of the Joint Programming for Neurodegenerative Diseases program, funded by the European Commission. He has received grant support from the German Research Foundation (DFG), the German Federal Ministry of Education and Research (BMBF), the Ministry for Science, Research and Art Baden‐Württemberg (MWK), the European Commission, the Helmholtz Association and the Michael J. Fox Foundation. Dr Benjamin Röben has received a research grant from the University of Tuebingen (Clinician Scientist; Project‐Nr. 480‐0‐0). Dr Nicole Schneiderhan‐Marra has received funding from the State Ministry of Baden‐Württemberg for Economic Affairs, Labour and Tourism (Predictive Diagnostic of Immune‐associated Diseases for Personalized Medicine, AZ 35‐4223.10/8). Dr Isabel Wurster receives funding from the Michael J. Fox Foundation as an Edmond J. Safra Fellow in Movement Disorders. Dr Milan Zimmermann has received a research grant from the University of Tuebingen (Clinician Scientist; Project‐Nr. 481‐0‐0) and the remaining authors have nothing to disclose.

ETHICS STATEMENT

All participants gave written informed consent. The study was approved by the Ethics Committee of the Faculty of Medicine at the University of Tuebingen (Project‐Nr. 458/2023BO2).

Supporting information

Data S1.

ACKNOWLEDGEMENTS

CSF samples were obtained from the Neuro‐Biobank of the University of Tuebingen, Germany (https://www.hih‐tuebingen.de/en/about‐us/core‐facilities/biobank/). The biobank is supported by the local university, the Hertie Institute and the DZNE. Open Access funding enabled and organized by Projekt DEAL.

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.
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