Serum matrix metalloproteinase-9 (MMP9) and amyloid-beta protein precursor (APP) as potential biomarkers in children with Fragile-X syndrome: A cross sectional study

INTRODUCTION

Fragile-X syndrome(FXS) is a neurological disease caused by abnormal repeats in the 5'untranslated region of the FMR1 gene leading to a defective fragile-X-messenger-ribonucleoprotein-1 (FMRP). Although relatively common in children, it is usually under-diagnosed especially in developing countries where genetic screening is not routinely practiced. So far, FXS lacks a laboratory biomarker that can be used for screening, severity scoring or therapeutic monitoring of potential new treatments.

METHODS

110 subjects were recruited; 80 male children with suspected FXS and 30 matched healthy children. We evaluated the clinical utility of serum matrix metalloproteinase-9(MMP9) and amyloid-beta protein precursor(APP) as potential biomarkers for FXS.

RESULTS

Out of 80 suspected children, 14 had full mutation, 8 had the premutation and 58 children had normal genotypes. No statistically-significant difference was detected between children with different genotypes concerning age of onset(P = 0.658), main clinical presentation(P = 0.388), clinical severity-score(P = 0.799), patient's disease-course(P = 0.719) and intellectual disability(P = 0.351). Both MMP9 and APP showed a statistically significant difference when comparing different genotype subgroups(P = 0.019 and < 0.001, respectively). Clinically, MMP9 levels were highest in children presenting with language defects, while APP was highest in children with neurodevelopmental delay. In receiver operating curve analysis, comparing full and premutation with the normal genotype group, MMP9 has an area-under-the-curve of 0.701(95 % CI 0.557-0.845), while APP was marginally better at 0.763(95 % CI 0.620-0.906). When combined together, elevated MMP9 or APP had excellent sensitivity > 95 % for picking-up FXS cases in the clinical setting.

CONCLUSIONS

Screening for circulating biomarkers in the absence of FXS genetic diagnosis is justified. Our study is the first to evaluate both MMP9 and APP in FXS suspected children in a clinical setting and to assess their correlation with disease presentation and severity.

Expression of the Tau Protein and Amyloid Protein Precursor Processing Genes in the CA3 Area of the Hippocampus in the Ischemic Model of Alzheimer's Disease in the Rat

Understanding the mechanisms underlying the selective susceptibility to ischemia of the CA3 region is very important to explain the neuropathology of memory loss after brain ischemia. We used a rat model to study changes in gene expression of the amyloid protein precursor and its cleaving enzymes and tau protein in the hippocampal CA3 sector, after transient 10-min global brain ischemia with survival times of 2, 7, and 30 days. The expression of the α-secretase gene was below control values at all times studied. But, the expression of the β-secretase gene was below the control values at 2-7 days after ischemia and the maximal increase in its expression was observed on day 30. Expression of the presenilin 1 gene was significantly elevated above the control values at 2-7 days after ischemia and decreased below the control values at day 30. Expression of the presenilin 2 gene showed an opposite trend to the expression of presenilin 1. Expression of the amyloid protein precursor gene after ischemia was at all times above the control values with a huge significant overexpression on day 7. Additionally, the expression of the tau protein gene was below the control values 2 days after ischemia, but the significant increase in its expression was observed on days 7-30. Data show that brain ischemia activates neuronal changes and death in the CA3 region of the hippocampus in a manner dependent on amyloid and tau protein, thus determining a new and important way to regulate the survival and/or death of ischemic neurons.

Opposing effects of APP/PS1 and TrkB.T1 genotypes on midbrain dopamine neurons and stimulated dopamine release in vivo

Brain derived neurotrophic factor (BDNF) signaling disturbances in Alzheimer׳s disease (AD) have been demonstrated. BDNF levels fall in AD, but the ratio between truncated and full-length BDNF receptors TrkB.T1 and TrkB.TK, respectively, increases in brains of AD patients and APPswe/PS1dE9 (APP/PS1) AD model mice. Dopaminergic (DAergic) system disturbances in AD and detrimental effects of BDNF signaling deficits on DAergic system functions have also been indicated. Against this, we investigated changes in nigrostriatal dopamine (DA) system in mice carrying APP/PS1 and/or TrkB.T1 transgenes, the latter line modeling the TrkB.T1/TK ratio change in AD. Employing in vivo voltammetry, we found normal short-term DA release in caudate-putamen of mice carrying APP/PS1 or TrkB.T1 transgenes but impaired capacity to recruit more DA upon prolonged stimulation. However, mice carrying both transgenes did not differ from wild-type controls. Immunohistochemistry revealed normal density of tyrosine hydroxylase positive axon terminals in caudate-putamen in all genotypes and intact presynaptic machinery for DA release and reuptake, as shown by unchanged levels of SNAP-25, α-synuclein and DA transporter. However, we observed increased DAergic neurons in substantia nigra of TrkB.T1 mice resulting in decreased tyrosine hydroxylase per neuron in TrkB.T1 mice. The finding of unchanged nigral DAergic neurons in APP/PS1 mice largely confirms earlier reports, but the unexpected increase in midbrain DA neurons in TrkB.T1 mice is a novel finding. We suggest that both APP/PS1 and TrkB.T1 genotypes disrupt DAergic signaling, but via separate mechanisms.