Growth Differentiation Factor 15 Is A Potential Biomarker For Parkinson’s Disease

Background:Parkinson’s disease(PD)is the second most common neurodegenerative disease just after Alzheimer’s disease(AD)in the world,and the numbers are projected to increase with age.The clinical manifestations are characterized by motor(such as rest tremor,rigidity,and bradykinesia)and non-motor syndromes(such as hyposmia,constipation,rapid eye movement sleep behavior disorder,depression and cognitive dysfunction).Presently,the diagnosis of PD is primarily based on clinical criteria,despite using these strict criteria,we fail to diagnose all PD patients accurately.The signs and symptoms of PD overlap with those of other neurological disorders such as multiple system atrophy,progressive supranuclear palsy,or corticobasal degeneration.Onset of each of these conditions is insidious and presentation can be heterogeneous,making early diagnosis particularly susceptible to error.There is a fast growing need for the development of biomarkers for early diagnosis of PD,as well as monitoring disease progression and evaluating treatment response.Growth differentiation factor 15(GDF-15)is a member of the transforming growth factor beta(TGF-P)superfamily,expressed in the kidney,brain,lung,heart,liver,placenta and prostate.It is a stress responsive cytokine playing an important regulatory role in inflammation and pro/anti-apoptosis in diseased and injured tissues.GDF15 is widely distributed in the central and peripheral nervous system.GDF15 plays an important role in the development and progression of several neurological diseases including stroke and neurodegenerative disease.Clinical researches have indicated that GDF-15 is an independent risk marker for disability in patients with stroke.Serum GDF15 levels are elevated above normal in patients with neurodegenerative diseases,such as AD.In the animal research,GDF15 was shown to be protective for nigrostriatal dopaminergic neurons,however,other studies just show the opposite effect.It has been reported that cerebrospinal fluid(CSF)GDF15 levels in patients with PD dementia were significantly higher than PD non-dementia(PDND)patients,and negatively correlated with cognitive function.Presently,little is known about the effect of serum GDF15 on dopaminergic neurons in humans.Fibroblast growth factor 21(FGF21)belongs to the fibroblast growth factor superfamily,with diverse biological functions in cell growth and cell differentiation.It is an important endocrine and paracrine regulator of glucose and fatty acid metabolism.As for central nervous system,FGF21 is expressed in different regions of the brain,specifically regions of the midbrain,including substantia nigra where the dopaminergic neurons are abundant.Recently,an in vitro study reported the presence of FGF21 in the midbrain and its expression by glial cells in culture,and showed that FGF21 could enhance mitochondrial respiratory capacity in dopaminergic neurons.However,the expression of FGF21 in PD patients has never been detected,and whether it has a protective effect on dopaminergic neurons is still unknown.Objective:This study detected the serum GDF15 and FGF21 levels in PD patients,investigated associations between these two proteins and clinical parameters,and found possible biomarkers for PD.Methods:Idiopathic PD patients and age-matched controls(n=104 and 88,respectively)were enrolled.For the PD subjects,information regarding gender,age,body mass index(BMI),disease duration,age at onset of Parkinsonism,duration of levodopa medication,and levodopa equivalent daily dose(LEDD)were collected.The motor severity of PD was evaluated according to the Unified Parkinson’s Disease Rating Scale(UPDRS-Ⅲ)score which was conducted during the off-medication phase.Serum GDF15 and FGF21 levels were measured by human enzyme-linked immunosorbent assay(ELISA).Univariate and multivariate analyses investigated correlations between GDF15 and clinical characteristics,including disease severity by the UPDRS-III.The diagnostic value of GDF15 was evaluated by receiver operating characteristic curve(ROC)analysis.Results:1.Basic characteristics for PD patients and controlsTo determine whether there was a significant difference in GDF15 levels between the PD patients and controls,we used a standard 2-sample t-test.The mean GDF15 level of the PD group(573.50 pg/mL)was about 2-fold that of the control group(288.23 pg/mL;P = 0.000).Moreover,when stratified by gender,the difference was substantially significant as well.The GDF15 levels of both men and women in the PD group(650.94 pg/mL and 498.98 pg/mL,respectively)were significantly higher than that of the men and women in the control group(308.54 pg/mL,P = 0.000 for men;268.83 pg/mL,P = 0.000 for women).However,unlike GDF15,FGF21 presented an insignificant difference between the two groups(PD vs control:425.26 pg/mL vs 407.88 pg/mL,P =0.602).When stratified by gender,the difference was insignificant as well.2.Clinical characteristics of men and women in the PD groupIn the PD group,the GDF15 levels of the men(650.94 pg/mL)were significantly higher than that of the women(498.98 pg/mL,P = 0.001).However,in the control group the GDF15 levels of the men(308.54 pg/mL)were similar to that of the women(268.83 pg/mL;P = 0.164).Serum FGF21 levels of male and female PD patients was 451.91 pg/mL and 399.62 pg/mL,respectively(P = 0.26),and therefore statistically similar.The men and women with PD were statistically similar in age,BMI,disease duration,age at onset of parkinsonism,duration of levodopa medication,LEDD,and UPDRS-Ⅲ score.3.Associations between GDF15 levels and clinical parameters in the PD groupThe correlation analysis showed that the serum GDF15 level was significantly and positively associated with age(r = 0.236,P = 0.016),disease duration(r = 0.231,P = 0.019),UPDRS-Ⅲscore(r = 0.386,P = 0.000),and male gender(r = 0.320,P = 0.001).However,no significant association was found between GDF15 and BMI(r = 0.013,P = 0.896),age at onset of parkinsonism(r = 0.158,P= 0.109),LEDD(r = 0.164,P = 0.097),duration of levodopa medication(r = 0.151,P=0.127),or use of dopamine receptor agonists(r = 0.061,P = 0.535).4.The multiple linear regression analysis of UPDRS-Ⅲ scoreWe used univariate and multiple linear regression analyses to identify potential risk factors for motor severity of PD,as reflected by the UPDRS-Ⅲ score.According to the results of the univariate analysis,the following were significantly associated with the UPDRS-Ⅲ score:disease duration(β=1.978,P= 0.000);LEDD(β=0.016,P=0.004);duration of levodopa medication(β=0.141,P = 0.000);and GDF15 level(P = 0.020,P = 0.000).We then performed a stepwise multiple linear regression analysis,adjusting for age,gender,disease duration,LEDD,and duration of levodopa medication.The results revealed that disease duration(β=1.659,P =0.000)and serum GDF15 level(β= 0.015,P=0.001)were independent risk factors that correlated with UPDRS-III score.5.ROC curve analysis of GDF15 as a possible PD biomarkerTo evaluate the utility of GDF15 as a candidate marker for discriminating the PD patients from the normal controls,an ROC curve analysis was performed.For all PD patients,an optimal cut-off value of 436.56 pg/mL for GDF15 was identified,and the AUC was 0.860(95%CI 0.803-0.906,P<0.0001),with a sensitivity of 71.15%and specificity of 87.50%.For men,the AUC was 0.891(95%CI 0.809-0.946,P<0.0001),with a sensitivity of 76.47%and specificity of 93.02%,where the best cut-off concentration of GDF15 was 474.49 pg/mL.Compared with men,women showed a lower sensitivity of 62.26%and specificity of 88.89%.The AUC of women with PD was 0.836(95%Cl 0.748-0.903,P<0.0001),and the optimal cut-off value of GDF15 was 427.63 pg/mL.Conclusion:Serum GDF15 levels were substantially elevated in PD patients compared with healthy age-matched controls and correlated with worsening of motor function.GDF15 may be a potential biomarker for diagnosis and monitoring motor severity in PD.