BackgroundLoss-of-function mutations in PINK1 and PARKIN are the most common causes of autosomal recessive Parkinson’s disease (PD). PINK1 is a mitochondrial serine/threonine kinase that plays a critical role in mitophagy, a selective autophagic clearance of damaged mitochondria. Accumulating evidence suggests mitochondrial dysfunction is one of central mechanisms underlying PD pathogenesis. Therefore, identifying regulatory mechanisms of PINK1 expression may provide novel therapeutic opportunities for PD. Although post-translational stabilization of PINK1 upon mitochondrial damage has been extensively studied, little is known about the regulation mechanism of PINK1 at the transcriptional or translational levels.ResultsHere, we demonstrated that microRNA-27a (miR-27a) and miR-27b suppress PINK1 expression at the translational level through directly binding to the 3′-untranslated region (3′UTR) of its mRNA. Importantly, our data demonstrated that translation of PINK1 is critical for its accumulation upon mitochondrial damage. The accumulation of PINK1 upon mitochondrial damage was strongly regulated by expression levels of miR-27a and miR-27b. miR-27a and miR-27b prevent mitophagic influx by suppressing PINK1 expression, as evidenced by the decrease of ubiquitin phosphorylation, Parkin translocation, and LC3-II accumulation in damaged mitochondria. Consequently, miR-27a and miR-27b inhibit lysosomal degradation of the damaged mitochondria, as shown by the decrease of the delivery of damaged mitochondria to lysosome and the degradation of cytochrome c oxidase 2 (COX2), a mitochondrial marker. Furthermore, our data demonstrated that the expression of miR-27a and miR-27b is significantly induced under chronic mitophagic flux, suggesting a negative feedback regulation between PINK1-mediated mitophagy and miR-27a and miR-27b.ConclusionsWe demonstrated that miR-27a and miR-27b regulate PINK1 expression and autophagic clearance of damaged mitochondria. Our data further support a novel negative regulatory mechanism of PINK1-mediated mitophagy by miR-27a and miR-27b. Therefore, our results considerably advance our understanding of PINK1 expression and mitophagy regulation and suggest that miR-27a and miR-27b may represent potential therapeutic targets for PD.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-016-0121-4) contains supplementary material, which is available to authorized users.

Accumulation of amyloid β (Aβ) in the brain is a key pathological hallmark of Alzheimer’s disease (AD). Because aging is the most prominent risk factor for AD, understanding the molecular changes during aging is likely to provide critical insights into AD pathogenesis. However, studies on the role of miRNAs in aging and AD pathogenesis have only recently been initiated. Identifying miRNAs dysregulated by the aging process in the brain may lead to novel understanding of molecular mechanisms of AD pathogenesis. Here, we identified that miR-186 levels are gradually decreased in cortices of mouse brains during aging. In addition, we demonstrated that miR-186 suppresses β-site APP-cleaving enzyme 1 (BACE1) expression by directly targeting the 3′UTR of Bace1 mRNA in neuronal cells. In contrast, inhibition of endogenous miR-186 significantly increased BACE1 levels in neuronal cells. Importantly, miR-186 overexpression significantly decreased Aβ level by suppressing BACE1 expression in cells expressing human pathogenic mutant APP. Taken together, our data demonstrate that miR-186 is a potent negative regulator of BACE1 in neuronal cells and it may be one of the molecular links between brain aging and the increased risk for AD during aging.

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MicroRNAs are emerging as promising biomarkers for diagnosis of various diseases. Notably, cerebrospinal fluid (CSF) contains microRNAs that may serve as biomarkers for neurological diseases. However, there has been a lack of consistent findings among CSF microRNAs studies. Although such inconsistent results have been attributed to various technical issues, inherent biological variability has not been adequately considered as a confounding factor. To address this critical gap in our understanding of microRNA variability, we evaluated intra-individual variability of microRNAs by measuring their levels in the CSF from healthy individuals at two time points, 0 and 48 hours. Surprisingly, the levels of most microRNAs were stable between the two time points. This suggests that microRNAs in CSF may be a good resource for the identification of biomarkers. However, the levels of 12 microRNAs (miR-19a-3p, miR-19b-3p, miR-23a-3p, miR-25a-3p, miR-99a-5p, miR-101-3p, miR-125b-5p, miR-130a-3p, miR-194-5p, miR-195-5p, miR-223-3p, and miR-451a) were significantly altered during the 48 hours interval. Importantly, miRNAs with variable expression have been identified as biomarkers in previous studies. Our data strongly suggest that these microRNAs may not be reliable biomarkers given their intrinsic variability even within the same individual. Taken together, our results provide a critical baseline resource for future microRNA biomarker studies.

Introduction Epigenetic stimuli induce beneficial or detrimental changes in gene expression, and consequently, phenotype. Some of these phenotypes can manifest across the lifespan—and even in subsequent generations. Here, we used a mouse model of vascular cognitive impairment and dementia (VCID) to determine whether epigenetically induced resilience to specific dementia‐related phenotypes is heritable by first‐generation progeny. Methods Our systemic epigenetic therapy consisted of 2 months of repetitive hypoxic “conditioning” (RHC) prior to chronic cerebral hypoperfusion in adult C57BL/6J mice. Resultant changes in object recognition memory and hippocampal long‐term potentiation (LTP) were assessed 3 and 4 months later, respectively. Results Hypoperfusion‐induced memory/plasticity deficits were abrogated by RHC. Moreover, similarly robust dementia resilience was documented in untreated cerebral hypoperfused animals derived from RHC‐treated parents. Conclusions Our results in experimental VCID underscore the efficacy of epigenetics‐based treatments to prevent memory loss, and demonstrate for the first time the heritability of an induced resilience to dementia.

Recent evidence from our laboratory documents functional resilience to retinal ischemic injury in untreated mice derived from parents exposed to repetitive hypoxic conditioning (RHC) before breeding. To begin to understand the epigenetic basis of this intergenerational protection, we used methylated DNA immunoprecipitation and sequencing to identify genes with differentially methylated promoters (DMGPs) in the prefrontal cortex of mice treated directly with the same RHC stimulus (F0-RHC) and in the prefrontal cortex of their untreated F1-generation offspring (F1-*RHC). Subsequent bioinformatic analyses provided key mechanistic insights into how changes in gene expression secondary to promoter hypo- and hypermethylation might afford such protection within and across generations. We found extensive changes in DNA methylation in both generations consistent with the expression of many survival-promoting genes, with twice the number of DMGPs in the cortex of F1*RHC mice relative to their F0 parents that were directly exposed to RHC. In contrast to our hypothesis that similar epigenetic modifications would be realized in the cortices of both F0-RHC and F1-*RHC mice, we instead found relatively few DMGPs common to both generations; in fact, each generation manifested expected injury resilience via distinctly unique gene expression profiles. Whereas in the cortex of F0-RHC mice, predicted protein-protein interactions reflected activation of an anti-ischemic phenotype, networks activated in F1-*RHC cortex comprised networks indicative of a much broader cytoprotective phenotype. Altogether, our results suggest that the intergenerational transfer of an acquired phenotype to offspring does not necessarily require the faithful recapitulation of the conditioning-modified DNA methylome of the parent.

Several decades of research support the phenomenon of epigenetic conditioning, wherein a stressful, but not damaging, stimulus promotes a protective phenotype against an otherwise detrimental injury. Epigenetics involves changes in gene expression without changing DNA sequence, and occurs through three fundamental mechanisms: DNA methylation, histone modifications, and noncoding RNAs. Recent findings in our lab show that this induced adaptive response can be transmitted intergenerationally to first‐generation offspring. Specifically, using repetitive hypoxic conditioning (RHC) as an epigenetic stimulus, we documented reduced retinal ischemic injury not only in the animals that were treated with RHC, but also in their untreated F1 generation adult offspring. In this study, we investigate whether this adaptive response also occurs in the brain and how such epigenetic mechanisms manifest a protective effect within and across generations. Using methylated DNA immunoprecipitation and sequencing (meDIP‐seq), genome‐wide DNA methylation sites were identified in samples of cerebral cortex of the following animal groups: direct RHC‐treated F0 mice (F0‐RHC), their matched controls (F0‐CTL), the F1 mice derived from mating pairs of F0 RHC mice (F1‐RHC) and mating pairs of control mice (F1‐CTL). Differentially methylated regions (DMRs) on gene promoters were identified and compared between control and RHC‐treated mice at each generation. We identified 3059 DMRs (1549 hypermethylated, 1510 hypomethylated) between F0‐RHC and F0‐CTL in the F0 generation, and 4818 DMRs (2266 hypermethylated and 2552 hypomethylated) between F1‐RHC and F1‐CTL in the F1 generation. Subsequent bioinformatic analysis (Ingenuity Pathway Analysis [IPA], Qiagen) yielded 1405 differentially expressed (based on activated z‐scores) genes (719 down, 686 up) between RHC and control cortex in the F0 generation, with 220 unique molecules being enriched in 58 IPA‐designated pathways. In the F1 generation, 2105 differentially expressed genes (986 down, 1119 up) were identified between F1‐RHC and F1‐CTL, comprised of 317 unique molecules enriched in 79 IPA‐designated pathways. 52 of these genes were similarly hyper‐ or hypo‐methylated in each generation. Notably, both F0‐RHC and F1‐RHC generations exhibited a downregulation of pathways identified by IPA relating to “neurological disease.” However, further interrogation of these pathways reveal that directionally‐appropriate changes in ischemia‐related genes largely define the F0‐RHC cortex, whereas the F1‐RHC cortex is enriched in genes that collectively provide defense against broader categories of neurodegeneration. Thus, mechanisms underlying resilience in F0 cerebral cortex directly treated with our RHC stimulus are not directly replicated in the brain of animals that inherit resilience from their treated F0 parents. These results indicate that the cortical DNA methylome is responsive to our RHC stress, and thus may participate in the epigenetic establishment of injury‐resilient CNS phenotypes both within and between generations.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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