PARP-1 and p53 Regulate the Increased Susceptibility to Oxidative Death of Lymphocytes from MCI and AD Patients

Abstract

Mild cognitive impairment (MCI) is a clinically detectable initial stage of cognitive deterioration with a high conversion rate to dementia. There is increasing evidence that some of the cerebral alterations present in Alzheimer type dementia can be found in peripheral tissues. We have previously shown that lymphocytes from Alzheimer’s disease (AD) patients have increased susceptibility to hydrogen peroxide (H2O2)-induced death that depends on dementia severity. We here investigated whether lymphocytes from MCI patients show increased vulnerability to death, and explored the involvement of Poly [ADP-ribose] polymerase (PARP-1) and p53 in the regulation of this process. Lymphocytes from 16 MCI and 10 AD patients, and 15 healthy controls (HCs) were submitted to increasing concentrations of H2O2 for 20 h. Cell death was determined by flow cytometry, in the presence or absence of PARP-1 inhibitors (3-aminobenzamide (3-ABA) or Nicotinamide (NAM)), or the p53 inhibitor (nutlin-3) or stabilizer (pifithrin-α). PARP-1 and p53 mRNA levels were determined by quantitative PCR (qPCR). Lymphocytes from MCI patients showed increased susceptibility to death, attaining intermediate values between AD and controls. PARP inhibitors -3-ABA and NAM- markedly protected from H2O2-induced death, making the difference between MCI and controls disappear, but not the difference between AD and controls. PARP-1 mRNA expression was increased in MCI lymphocytes. Modulation of p53 with Nutlin-3 or pifithrin-α did not modify the H2O2-induced death of lymphocytes from MCI or AD patients, but augmented the death in control lymphocytes attaining levels similar to MCI and AD. Accordingly, p53 mRNA expression was increased in AD and MCI lymphocytes compared to controls. In all, these results show that increased oxidative death is present in lymphocytes at the MCI stage. PARP-1 has a preponderant role, with complete death protection achieved with PARP inhibition in MCI lymphocytes, but not in AD, suggesting that PARP-1 might have a protective role. In addition, deregulations of the p53 pathway seem to contribute to the H2O2-induced death in MCI and AD lymphocytes, which show increased p53 expression. The results showing a prominent protective role of PARP inhibitors opens the door to study the use of these agents to prevent oxidative death in MCI patients.

Cancer Imprints an Increased PARP-1 and p53-Dependent Resistance to Oxidative Stress on Lymphocytes of Patients That Later Develop Alzheimer's Disease

“…Caregivers of patients with severe dementia provided the consent. Three patients from the healthy control and cancer group were analyzed in previous reports (Behrens et al, 2012 ; Salech et al, 2017 ), but donated new blood samples. For the diagnosis of AD the guidelines of Alzheimer's Association and the National Institute on Aging (McKhann et al, 2011 ) were followed and dementia severity was rated with the CDR (Morris, 1997 ).…”

“…The effects of p53 modulation were studied by the addition of the p53 inhibitor, Pifithrin-α (20 μM), or stabilizer, Nutlin-3 (10 μM), added 30 min before H 2 O 2 exposure. Samples containing roughly 1 × 10 6 cells were analyzed by flow cytometry following propidium iodide (PI) staining, in which viable (PI-negative), apoptotic (PI-positive, hypodiploid), and necrotic (PI-positive diploid) cells were distinguished (Behrens et al, 2011 , 2012 ; Ponce et al, 2014 ; Salech et al, 2017 ).…”

“…We here investigated the death of lymphocytes induced by H 2 O 2 in survivors of any type of cancer and in survivors of cancer who later developed AD (Ca&AD). In addition, we investigated the role of PARP-1 and p53 on the regulation of the susceptibility to oxidative death in these two groups of patients and compared them with the results previously reported in AD lymphocytes (Salech et al, 2017 ), in order to elucidate the involvement of the cell repair machinery in the inverse susceptibility to oxidative death of lymphocytes from cancer and AD patients.…”

“…In previous studies, we showed that the susceptibility of lymphocytes to cell death induced by H 2 O 2 in patients with cognitive impairment is dependent on both PARP-1 an p53 activity (Salech et al, 2017 ). In AD patients PARP-1 inhibition caused significant protection from H 2 O 2 -induced death, but did not reach control levels, suggesting that other cell death mechanisms are involved.…”

“…Accordingly, we demonstrated that lymphocytes from AD patients show an increased susceptibility to death by H 2 O 2 exposure, whereas those from skin cancer patients show increased survival, compared with lymphocytes from healthy control donors, without cognitive impairment, or cancer history of similar age and sex (Behrens et al, 2012 ). In addition, we showed that in patients with dementia, the H 2 O 2 lymphocyte death susceptibility increased in magnitude with the severity of the disease (Ponce et al, 2014 ), and is also present in the early stages of the disorder, in patients with mild cognitive impairment (MCI) (Salech et al, 2017 ).…”