Biometals in rare neurodegenerative disorders of childhood

Targeting Higher Levels of Tau Protein in Ukrainian Patients with Wilson's Disease

INTRODUCTION

Wilson's disease (WD) is a rare genetic disorder of copper metabolism in which impaired copper homeostasis may enhance amyloid aggregation and trigger neurodegeneration. Tau protein is a highly soluble microtubule-associated phosphoprotein that plays a significant role in microtubule stabilization; it is also a critical component of neurotoxic degenerative mechanisms. Tau has been shown to be involved in neuronal degeneration and axonal damage, and impaired copper metabolism has been shown to be involved in copper intoxication and thus associated with the processes of neurodegeneration and cellular damage. We have therefore investigated tau protein as a potential marker of axonal impairment and neurodegeneration.

METHODS

Patients with WD (n = 47; mean age ± standard deviation [SD] 30.19 ± 7.87 years; mean disease duration : 10.06 ± 3.9 years) and healthy controls (HC; n = 30; mean age 29.6 ± 4.73 years) were tested for serum tau protein levels using an enzyme-linked immunosorbent assay method. All patients were receiving a stable penicillamine dose as ongoing therapy.

RESULTS

Patients with WD had a higher mean tau protein level than did the HC (221.7 ± 135.1 vs. 71.14 ± 20.56 pg/mL, p < 0.0001). Patients with WD also had abnormally high serum tau protein levels (t statistic 6.047, 95% confidence interval - 218.2 to - 95.86) in both the cerebral and hepatocerebral forms of WD, with patients having the cerebral form showing a tendency toward higher tau levels. We found that tau protein did not differ according to gender, disease duration, age at disease onset, ceruloplasmin serum level and copper serum level.

CONCLUSION

This study provides novel data revealing that high tau protein levels in WD patients could be a potential biomarker for axonal impairment and possible neuronal damage due to tau protein, leading to neurodegeneration in WD.

Copper as a key regulator of cell signalling pathways

Copper is an essential element in many biological processes. The critical functions associated with copper have resulted from evolutionary harnessing of its potent redox activity. This same property also places copper in a unique role as a key modulator of cell signal transduction pathways. These pathways are the complex sequence of molecular interactions that drive all cellular mechanisms and are often associated with the interplay of key enzymes including kinases and phosphatases but also including intracellular changes in pools of smaller molecules. A growing body of evidence is beginning to delineate the how, when and where of copper-mediated control over cell signal transduction. This has been driven by research demonstrating critical changes to copper homeostasis in many disorders including cancer and neurodegeneration and therapeutic potential through control of disease-associated cell signalling changes by modulation of copper-protein interactions. This timely review brings together for the first time the diverse actions of copper as a key regulator of cell signalling pathways and discusses the potential strategies for controlling disease-associated signalling processes using copper modulators. It is hoped that this review will provide a valuable insight into copper as a key signal regulator and stimulate further research to promote our understanding of copper in disease and therapy.

The relevance of metals in the pathophysiology of neurodegeneration, pathological considerations

Neurodegenerative disorders are featured by a variety of pathological conditions that share similar critical processes, such as oxidative stress, free radical activity, proteinaceous aggregations, mitochondrial dysfunctions, and energy failure. They are mediated or triggered by an imbalance of metal ions leading to changes of critical biological systems and initiating a cascade of events finally leading to neurodegeneration and cell death. Their causes are multifactorial, and although the source of the shift in oxidative homeostasis is still unclear, current evidence points to changes in the balance of redox transition metals, especially iron, copper, and other trace metals. They are present at elevated levels in Alzheimer disease, Parkinson disease, multisystem atrophy, etc., while in other neurodegenerative disorders, copper, zinc, aluminum, and manganese are involved. This chapter will review the recent advances of the role of metals in the pathogenesis and pathophysiology of major neurodegenerative diseases and discuss the use of chelating agents as potential therapies for metal-related disorders.