MicroRNAs (miRNAs) are small non-coding RNA which have been shown to regulate gene expression. The alteration ofmiRNAs expression has been associated with several pathological processes, including neurodegeneration. In the search for easily accessible and non-invasive biomarkers for Alzheimer's disease (AD) diagnosis and prognosis, circulating miRNAs are among the most promising candidates. Some of them have been consistently identified as AD-specific miRNAs and their targets also seem implicated in pathophysiological processes underlying AD. Here, we review the emerging role for miRNA in AD, giving an overview on general miRNAs biology, their implications in AD pathophysiology and their potential role as future biomarkers.

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The emerging role of microRNAs in Alzheimer's disease

In the 12 years since the publication of the first Consensus Paper of the WFSBP on biomarkers of neurodegenerative dementias, enormous advancement has taken place in the field, and the Task Force t...

https://www.tandfonline.com/doi/pdf/10.1080/15622975.2017.1375556

Cerebrospinal fluid and blood biomarkers for neurodegenerative dementias: An update of the Consensus of the Task Force on Biological Markers in Psychiatry of the World Federation of Societies of Biological Psychiatry

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the leading cause of cognitive and behavioral impairment in industrialized societies. The cause of AD is unknown and the major risk factor for AD is age. About 5% of all AD cases have a genetic or familial cause however the vast majority of all AD cases (~95%) are of sporadic origin. Both the familial and the sporadic forms of AD share a common disease phenotype involving at least eight characteristic features including (i) evidence of uncontrolled oxidative stress; (ii) up-regulated pro-inflammatory signaling; (iii) changes in innate-immune signaling; (iv) the progressive accumulation of lesions including neurofibrillary tangles (NFT) and amyloid beta (Aβ)-containing senile plaques (SP); (v) significant synaptic signaling deficits; (vi) neurite and brain cell atrophy; (vii) progressively altered gene expression patterns that are different from healthy brain aging; and (viii) progressive cognitive impairment and dementia in the host. There is currently no cure or adequate clinical treatment for AD, and it remains unclear how AD originates and propagates throughout the brain and central nervous system (CNS). Results from recent genome-wide association studies (GWAS) indicate that a significant portion of AD-relevant gene signals are not located within gene coding regions suggesting the contribution of epigenetic or environmental factors to AD risk. The potential contribution of pathogenic microbes to aging and AD is becoming increasingly recognized (Miklossy, 2011; Cho and Blaser, 2012; Bhattacharjee and Lukiw, 2013; Poole et al., 2013; Heintz and Mair, 2014; Huang et al., 2014; Mancuso et al., 2014). Importantly, most of the changes seen in AD, such as inflammation, brain cell atrophy, immunological aberrations, amyloidogenesis, altered gene expression and cognitive deficits are also seen as a consequence of microbial infection (Cho and Blaser, 2012; Yatsunenko et al., 2012; Bhattacharjee and Lukiw, 2013; Foster and McVey Neufeld, 2013; Kim et al., 2013; Heintz and Mair, 2014; Mancuso et al., 2014). This brief communication will review some recent observations on the potential contribution of pathogens to neurological dysfunction, with specific reference to AD wherever possible.

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Pathogenic microbes, the microbiome, and Alzheimer’s disease (AD)

Alzheimer's disease (AD) is a progressive and devastating neurodegenerative disorder. It is the leading cause of dementia in the world's rapidly growing aging population. The characteristics of AD are memory loss and cognitive impairment, meaning patients cannot carry out their daily activities independently. The increase of AD cases poses heavy burdens on families, society and the economy. Despite frequent efforts being made to research the etiology of AD, the causes of AD remain unknown, and no curative treatments are available yet. The pathological hallmarks of AD are amyloid plaques and neurofibrillary tangles in the brain. MicroRNAs are endogenous ∼22 nucleotides non-coding RNAs that could regulate gene expression at a post-transcriptional level by transcript degradation or translation repression. MicroRNAs are involved in many biological processes and diseases, particularly multifactorial diseases, providing an excellent tool with which to research the mechanisms of these diseases. AD is a multifactorial disorder, and accumulating evidence shows that microRNAs play a critical role in the pathogenesis of AD. In this review, we will highlight the effect of microRNAs in different pathological processes throughout AD progression.

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MicroRNAs in Alzheimer's Disease.

Exosomal miRNAs in central nervous system diseases: biomarkers, pathological mediators, protective factors and therapeutic agents.

MicroRNAs (miRNA) are biological molecules transcribed from non-protein coding regions of the genome, participating in regulating cellular processes. MiRNAs in biofluids may possess neurodegenerative disease biomarker potential for screening tests, differential diagnosis and disease progression monitoring. This systematic review clarifies biomarker potential of miRNAs detected in biofluids of neurodegenerative disease patients. Thirty-three and ten miRNAs displayed significant expression between patients with multiple sclerosis and Alzheimer's disease, respectively, compared to healthy controls in minimum two studies. Thirty-eight miRNAs showed biomarker potential by distinguishing significantly between minimum two diseases. Summarized data directs future research towards discovering new biomarkers for neurodegenerative diseases.

The potential of microRNAs as biofluid markers of neurodegenerative diseases – a systematic review

Pre-analytical factors influencing the stability of cerebrospinal fluid proteins.

Background Sexual dysfunction is a common adverse effect of selective serotonin reuptake inhibitors (SSRIs) and there is a concern that the sexual harms might persist after discontinuation of therapy. Objective To assess whether the use of SSRIs in animals can lead to persistent sexual dysfunction. Methods Systematic review of animal studies measuring sexual behaviour after end of treatment with SSRIs or serotonin norepinephrine reuptake inhibitors. Data sources We searched PubMed and EMBASE. Results We included 14 studies. The general quality of the studies was poor. Only four studies reported use of randomisation and none mentioned allocation concealment. All studies used placebo and were therefore blinded. For rats exposed to SSRIs compared with those exposed to placebo, we found a higher risk of no mounting behaviour (RR = 0.73; 95% CI = 0.62-0.86), no intromission behaviour (RR = 0.74; 95% CI = 0.60-0.92) and no ejaculation behaviour (RR = 0.49, 95% CI = 0.24-1.00). Conclusion Our results showed substantial and lasting effects on sexual behaviour in rats after exposure to an SSRI early in life on important sexual outcomes.

Persistent sexual dysfunction after early exposure to SSRIs: Systematic review of animal studies

Extended‐release methylphenidate for attention deficit hyperactivity disorder (ADHD) in adults

Background Millions of people are treated with antidepressants like selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs). This clinical practice is based on short-term trials that have exaggerated the benefits and underestimated the harms. We also know too little about long-term harms. Aim To assess harms of SSRIs and SNRIs that persist after end of drug intake. Methods Systematic review of placebo-controlled randomised trials of any length in patients with a psychiatric diagnosis and a follow-up of at least six months. Our primary outcomes were mortality, functional outcomes, quality of life and core psychiatric events. We searched PubMed, Embase, and the Cochrane Central Register of Controlled Trials and checked the references for eligible articles. One researcher extracted data and another checked the data extraction. Results Our searches returned 9,153 unique records. We included 22 papers for 12 trials on SSRIs. Median intervention and follow-up periods were 15 and 52 weeks, respectively. Median number of randomised participants was 51; only two trials had a drop-out rate below 20%.Outcome reporting was less thorough during follow-up than for the intervention period and only two trials maintained the blind during follow-up. All authors concluded that the drugs were not beneficial in the long term.All trials reported harms outcomes selectively or did not report any. Only two trials reported on any of our primary outcomes (school attendance and number of heavy drinking days). Conclusion The randomised trials currently available cannot be used to investigate persistent harms of antidepressants.

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Pia Brandt Danborg

Papers

The potential of microRNAs as biofluid markers of neurodegenerative diseases – a systematic review

Pre-analytical factors influencing the stability of cerebrospinal fluid proteins.

Persistent sexual dysfunction after early exposure to SSRIs: Systematic review of animal studies

Extended‐release methylphenidate for attention deficit hyperactivity disorder (ADHD) in adults

Long-term harms from previous use of selective serotonin reuptake inhibitors: A systematic review.