Apolipoprotein E Polymorphism and Oxidative Stress in Peripheral Blood-Derived Macrophage-Mediated Amyloid-Beta Phagocytosis in Alzheimer’s Disease Patients
Peripheral blood-derived macrophages isolated from Alzheimer’s disease (AD) patients have earlier been reported to demonstrate ineffective phagocytosis of amyloid-beta compared to the age-matched control subjects. However, the mechanisms causing unsuccessful phagocytosis remain unclear. Oxidative stress and the presence of ApoEε4 allele has been reported to play a major role in the pathogenesis of AD, but the contribution of oxidative stress and ApoEε4 in macrophage dysfunction leading to ineffective Aβ phagocytosis needs to be analyzed. Aβ phagocytosis assay has been performed using FITC-labeled Aβ and analyzed using flow cytometry and confocal imaging in patient samples and in THP-1 cells. Oxidative stress in patient-derived macrophages was analyzed by assessing the DNA damage using comet assay. ApoE polymorphism was analyzed using sequence-specific PCR and Hixson & Vernier Restriction isotyping protocol. In this study, we have analyzed the patterns of phagocytic inefficiency of macrophages in Indian population with a gradual decline in the phagocytic potential from mild cognitive impairment (MCI) to AD patients. Further, we have shown that the presence of ApoEε4 allele might also have a possible effect on the phagocytosis efficiency of the macrophages. Here, we demonstrate for the first time that oxidative stress could affect the amyloid-beta phagocytic potential of macrophages and hence by alleviating oxidative stress using curcumin, an anti-oxidant could enhance the amyloid-beta phagocytic efficacy of macrophages of patients with AD and MCI, although the responsiveness to curcumin might depends on the presence or absence of APOEε4 allele. Oxidative stress contributes significantly to decreased phagocytosis of Aβ by macrophages. Moreover, the phagocytic inefficiency of macrophages was correlated to the presence of ApoEε4 allele. This study also found that the Aβ-phagocytic potential of macrophage gets significantly enhanced in curcumin-treated patient-derived macrophages.
KeywordsAlzheimer’s disease Mild cognitive impairment Phagocytosis Internalization Colocalization Amyloid beta Macrophages Monocytes Curcumin APO E
We thank all the patients involved in the study.
MPS, RNM, JV and SG conceived and designed the study. JPS, DK, APM performed the experiments, acquired the results. JPS, APM, DK, MPS, RNM and SG analyzed, interpreted the results and drafted the manuscript. All authors reviewed and approved the manuscript. All authors verify that the data contained in the manuscript being submitted have not been previously published, have not been submitted elsewhere and will not be submitted elsewhere while under consideration at Cellular and Molecular Neurobiology.
This work was supported by the Indian Council of Medical Research, Government of India, Sanction Order No. 53/2/2011/CMB/BMS (GS) and research fellowship Council of Scientific and Industrial Research (JPS and APM) and Institute research fellowship from SCTIMST (DK).
Compliance with Ethical Standards
Conflict of interest
All authors declare that they have no conflict of interest.
All procedures performed in the above study were in accordance with the ethical standards of the Institutional Human Ethical Committee and with the 1964 Helsinki declaration and its later amendments or comparable standards.
Informed consent was obtained from all individual participants included in the study.