Golgi apparatus in Alzheimer’s disease

Abstract

Alzheimer’s disease (AD) is the most common cause of progressive and irreversiblepresenile and senile dementia of unavoidable tragicoutcome, affecting millions of humansworldwide. Even from the last decades of the 20 th century AD has become a seriousmedical challenge for aging population, inducing many ethical, legal, social, humanitarian, philosophical [1] and economic problems without an obvious perspective clarityfor the near future, despite the quotidian ongoing research [2]. The clinical phenomena of the disease are characterized by profound memory loss, visuo-spatial disorientation, loss of professional skills, learning inability, decline of speech fluency,gradual dysarthria,mood and behavioral disturbances and personality changes,phenomena which appear increasingly as the disease advances, complimented frequently by autonomic disorders andepileptic seizures, which progressively result in a final vegetative state, which is the common darkepilogue of the tragic life of the patients. The neuropathological profile of AD is plotted many years prior to phenomenological appearance of the disease. It consists of (a) abnormal accumulation of Aβ peptide in the form of neuritic plaques or diffusely dispersed in the neuropile and (b) intracellular accumulations of hyper-phosphorylated tau protein in the form of neurofibrillary tangles and (c) selective neuronal loss. All these findings, which compose the main neuropathological diagnostic criteria, as key hallmarks of AD [3,4] are usually observed, been dispersed in the hippocampus, the cortex of the cerebral hemispheres, and in many subcortical neuronal networks, which play a substantial role in cognition. Electron microscopy enlarged the horizons of morphological investigation in AD and revealed dendritic, spine andmarked synaptic pathology, in association with substantialorganelle alterations, involving mostly microtubules, mitochondria [5,6], Golgi apparatus (GA) [7] and endoplasmic reticulum (ER) [8] clearly observed even in areas of the brain, where dendritic plaques and neurofibrillary tangles are infrequent. The alterations of ER and GA result inaccumulation of misfolded proteins and neuronal loss [9], given that failure of the adaptive mechanisms of the unfolded protein response (UPR) may result in chronic accumulation of misfolded proteins in the ER [10] and impaired amyloid precursor protein (APP) processing and trafficking [11]. In addition Tau protein, which is accumulated in ER, Golgi complexes, and mitochondria [12], may activate the unfolded protein response by impairing ER-associated degradation [13]. In addition all newly synthesized proteins, which are used for membranic processes, insertion or secretion, axoplasmic or dendritic flow and synaptic activity, including APP, are practically processed through the vesicles and the cisternae of Golgi complex [14].