Molecular Changes in Circulating microRNAs' Expression and Oxidative Stress in Adults with Mild Cognitive Impairment: A Biochemical and Molecular Study

Abstract

Background: The release of miRNAs in tissue fluids significantly recommends its use as non-invasive diagnostic biomarkers for the progression and pathogenesis of mild cognitive impairment (MCI) in aged patients.

Objective: The potential role of circulated miRNAs in the pathogenesis of MCI and its association with cellular oxidative stress, apoptosis, and circulated BDNF, Sirtuin 1 (SIRT1), and dipeptidyl peptidase-4 (DPP4) were evaluated in older adults with MCI.

Methods: A total of 150 subjects aged 65.4±3.7 years were recruited in this study. The participants were classified into two groups: healthy normal (n=80) and MCI (n=70). Real-time PCR analysis was performed to estimate the relative expression of miRNAs; miR-124a, miR-483-5p, miR-142-3p, and miR-125b, and apoptotic-related genes Bax, Bcl-2, and caspase-3 in the sera of MCI and control subjects. In addition, oxidative stress parameters; MDA, NO, SOD, and CAT; as well as plasma DPP4 activity, BDNF, SIRT1 levels were colorimetrically estimated.

Results: The levels of miR-124a and miR-483-5p significantly increased and miR-142-3p and miR-125b significantly reduced in the serum of MCI patients compared to controls. The expressed miRNAs significantly correlated with severe cognitive decline, measured by MMSE, MoCA, ADL, and memory scores. The expression of Bax, and caspase-3 apoptotic inducing genes significantly increased and Bcl-2 antiapoptotic gene significantly reduced in MCI subjects compared to controls. In addition, the plasma levels of MDA, NO, and DPP4 activity significantly increased, and the levels of SOD, CAT, BDNF, and SIRT1 significantly reduced in MCI subjects compared to controls. The expressed miRNAs correlated positively with NO, MDA, DPP4 activity, BDNF, and SIRT-1, and negatively with the levels of CAT, SOD, Bcl-2, Bax, and caspase-3 genes.

Conclusion: Circulating miR-124a, miR-483-5p, miR-142-3p, and miR-125b significantly associated with severe cognitive decline, cellular oxidative stress, and apoptosis in patients with MCI. Thus, it could be potential non-invasive biomarkers for the diagnosis of MCI with high diagnostic performance.

Keywords: MCI; apoptosis; biomarkers; cellular oxidative stress; circulating miRNAs; real-time RT-PCR.

Figure 1

Changes in cellular oxidative stress; NO and MDA (A and B) and antioxidant enzymes; Cat and SOD the levels (C and D) in healthy control (n=80) and older adults with MCI (n=70). The results showed significant increase (p=0.001) in the levels of cellular NO and MDA in older adults with MCI compared to healthy controls (A and B). In addition, significant decrease (p=0.001) in the levels of antioxidant enzymes; CAT and SOD in older adults with MCI compared to healthy controls. Significance of the comparison was evaluated by Mann–Whitney-Wilcoxon test and sample t-test, ^{* *} p≤ 0.01, ^{* * *}p≤ 0.001.

Figure 2

Metabolic changes in the DPP4 activity, BDNF, SIRT-1, and apoptotic genes Bcl-2, Bax, and caspase-3 in healthy control (n=80) and older adults with MCI (n=70). (A–D). The results showed that the levels of BDNF, SIRT-1 significantly reduced and the levels of DPP4 activity significantly increased in older subjects with MCI compared to healthy controls (A–C). In addition, the expression of apoptotic genes was significantly reported in all subjects. In Older adults with MCI, the expression levels of both Bax and caspase-3 genes significantly (p=0.001) increased, and the expression levels of Bcl-2 gene significantly (p=0.01) reduced in comparison with the results of healthy controls (D). Significance of the comparison was evaluated by Mann–Whitney–Wilcoxon test and sample t-test, ^**p≤ 0.01 ^***p≤ 0.001.

Figure 3

MicroRNAs’ differential expression profile in healthy control (n=80) and older adults with MCI (n=70). The results showed that the relative expression of miR-124a and miR-483-5p significantly increased (P=0.001), and miR-142-3p, and miR-125b significantly reduced (P=0.01) in older adults with MCI compared healthy controls. Significance of the comparison was evaluated by Mann–Whitney–Wilcoxon test and sample t-test, **p≤ 0.01, ***p≤ 0.001.