Serliponaz Alfa’nın in vitro Alzheimer Hastalığı Modelinde Aβ Yüküne ve Erken Evre Otofaji ile ilişkili Yolaklara Etkisi

Abstract

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-beta (Aβ) peptides in the brain, resulting in the formation of extracellular senile plaques and intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein. It is the most common neurodegenerative disease, accompanied by neuronal loss and inflammation in the brain, with reduced cognitive function and dementia. Extracellular aggregation of amyloid-beta (Aβ) in the brain plays a central role in the onset and progression of Alzheimer’s disease (AD). Moreover, intraneuronal accumulation of Aβ via oligomer internalization might play an important role in the progression of AD. Lysosomes contain approximately 50 different enzymes that can degrade proteins, DNA, RNA, polysaccharides, and lipids. Mutations in the genes encoding these enzymes are responsible for over 30 genetic diseases called “lysosomal storage diseases” because they result in the accumulation of undegraded material in lysosomes. Most of these diseases are caused by the deficiency of a single lysosomal enzyme. One of these diseases, mutations in the CLN2 gene encoding the lysosomal enzyme Tripeptidyl peptidase-1 (TPP1), is associated with type 2 late infantile neuronal ceroid lipofuscinosis (LINCL2). However, there is limited information on the role of TPP1 in the pathogenesis of Alzheimer's disease (AD). Therefore, this study aimed to measure the reduction in intraneuronal Aβ accumulation using cerliponase alfa (CER) (Brineura®), a recombinant analogue of the TPP1 enzyme, and to determine whether autophagy pathways play a role in this reduction. In this study, Aβ accumulation in mouse hippocampal neuron cells (HT-22) was induced by exposure to fibrillar fAβ1-42. Cells were treated with CER (human recombinant rhTPP1; 1 mg/ml). Following exposure to fAβ1-42, the levels of intraneuronal soluble Aβ, TPP1, and key proteins associated with autophagy such as phosphorylated and total mammalian target of rapamycin (p-mTOR/mTOR), p62/sequestosome-1 (p62/SQSTM1), and microtubule-associated protein 1A/1B-light chain 3 (LC3) as well as the neuroprotective protein sirtuin-1 (SIRT1), were analyzed using the Western blot technique. Changes in the expression of sirtuin-1 (SIRT1), beclin-1 (BECN1), and autophagy related gene-5 (ATG5) genes were analyzed using RT-PCR, while the localization of Aβ, TPP1, p62, and LC3 was assessed through immunocytochemistry. Treatment with CER and fAβ1-42 resulted in an increase in mature TPP1 levels in HT-22 cells, which subsequently reduced the Aβ load. Furthermore, exposure to CER alone enhanced sirtuin-1 activity. Based on the current findings, this thesis suggests that TPP1 enzyme replacement therapy could represent a promising therapeutic strategy for the treatment of Alzheimer’s disease.