T lymphocytes apoptosis and mitochondrial membrane potential in Down's syndrome

Down syndrome is an oxidative phosphorylation disorder

Down syndrome is the most common genomic disorder of intellectual disability and is caused by trisomy of chromosome 21. Several genes in this chromosome repress mitochondrial biogenesis. The goal of this study was to evaluate whether early overexpression of these genes may cause a prenatal impairment of oxidative phosphorylation negatively affecting neurogenesis. Reduction in the mitochondrial energy production and a lower mitochondrial function have been reported in diverse tissues or cell types, and also at any age, including early fetuses, suggesting that a defect in oxidative phosphorylation is an early and general event in Down syndrome individuals. Moreover, many of the medical conditions associated with Down syndrome are also frequently found in patients with oxidative phosphorylation disease. Several drugs that enhance mitochondrial biogenesis are nowadays available and some of them have been already tested in mouse models of Down syndrome restoring neurogenesis and cognitive defects. Because neurogenesis relies on a correct mitochondrial function and critical periods of brain development occur mainly in the prenatal and early neonatal stages, therapeutic approaches intended to improve oxidative phosphorylation should be provided in these periods.

mitoXplorer, a visual data mining platform to systematically analyze and visualize mitochondrial expression dynamics and mutations

Mitochondria participate in metabolism and signaling. They adapt to the requirements of various cell types. Publicly available expression data permit to study expression dynamics of genes with mitochondrial function (mito-genes) in various cell types, conditions and organisms. Yet, we lack an easy way of extracting these data for mito-genes. Here, we introduce the visual data mining platform mitoXplorer, which integrates expression and mutation data of mito-genes with a manually curated mitochondrial interactome containing ∼1200 genes grouped in 38 mitochondrial processes. User-friendly analysis and visualization tools allow to mine mitochondrial expression dynamics and mutations across various datasets from four model species including human. To test the predictive power of mitoXplorer, we quantify mito-gene expression dynamics in trisomy 21 cells, as mitochondrial defects are frequent in trisomy 21. We uncover remarkable differences in the regulation of the mitochondrial transcriptome and proteome in one of the trisomy 21 cell lines, caused by dysregulation of the mitochondrial ribosome and resulting in severe defects in oxidative phosphorylation. With the newly developed Fiji plugin mitoMorph, we identify mild changes in mitochondrial morphology in trisomy 21. Taken together, mitoXplorer (http://mitoxplorer.ibdm.univ-mrs.fr) is a user-friendly, web-based and freely accessible software, aiding experimental scientists to quantify mitochondrial expression dynamics.

Lymphocyte subgroups and recurrent infections in children with Down syndrome - a prospective case control study

Down syndrome (DS) is the commonest genetic disorder and more liable for recurrent infections. We aimed to determine the differences in lymphocyte subgroups between DS children and the healthy population and to study the pattern and likelihood for recurrent infections and hospital admission due to infection. Our study was carried out in the Genetic Unit of Mansoura University Children’s Hospital, Egypt. The study enrolled 150 DS (DS group) and 100 controls (CG group). They were assessed for recurrent infections (including tonsillitis, otitis media [OM], pneumonia, upper respiratory tract infections [URTI], sinusitis, and gastroenteritis [GE]) and hospital admission due to infections. All patients were subjected to complete blood count and flow cytometric analysis for expression markers of B lymphocytes (CD19), natural killer (NK) cells (CD56), and T lymphocytes (CD3, CD4 and CD8). We found a statistically significant increase in the frequency of URTIs and sinusitis, OM, pneumonia, and hospital admission in the DS group. As regards the type of recurrent infection in DS, it was highest for URTIs and sinusitis. For age groups below 13 years, a statistically significant decrease in all studied CD markers was found in the DS group, while for the 13-18-year-olds, a statistically significant decrease was found in CD4, CD19, and CD56 in the DS group. Non-significant correlations were found between CD markers and recurrent infection and hospital admission. We concluded that lymphocyte subgroups that carry CD3, CD4, CD8, CD19, and CD56 were decreased in DS. Recurrent infections and hospital admission are still striking feature for DS but are not significantly correlated with lymphocyte subgroups.

Lymphocyte respiration in children with Trisomy 21

Background

This study measured lymphocyte mitochondrial O₂ consumption (cellular respiration) in children with trisomy 21.

Methods

Peripheral blood mononuclear cells were isolated from whole blood of trisomy 21 and control children and these cells were immediately used to measure cellular respiration rate. [O₂] was determined as a function of time from the phosphorescence decay rates (1/τ) of Pd (II)-meso-tetra-(4-sulfonatophenyl)-tetrabenzoporphyrin. In sealed vials containing lymphocytes and glucose as a respiratory substrate, [O₂] declined linearly with time, confirming the zero-order kinetics of O₂ conversion to H₂O by cytochrome oxidase. The rate of respiration (k, in μM O₂ min^-1), thus, was the negative of the slope of [O₂] vs. time. Cyanide inhibited O₂ consumption, confirming that oxidation occurred in the mitochondrial respiratory chain.

Results

For control children (age = 8.8 ± 5.6 years, n = 26), the mean (± SD) value of k_c (in μM O₂ per min per 10⁷ cells) was 1.36 ± 0.79 (coefficient of variation, Cv = 58%; median = 1.17; range = 0.60 to 3.12; -2SD = 0.61). For children with trisomy 21 (age = 7.2 ± 4.6 years, n = 26), the values of k_c were 0.82 ± 0.62 (Cv = 76%; median = 0.60; range = 0.20 to 2.80), p<0.001. Similar results (p<0.000) were obtained after excluding the five trisomy 21 children with elevated serum TSH (values >6.1 mU/L). Fourteen of 26 (54%) children with trisomy 21 had k_c values of 0.20 to 0.60 (i.e., <−2SD). The values of k_c positively correlated with body-mass index (BMI, R >0.302), serum creatinine (R >0.507), blood urea nitrogen (BUN, R >0.535) and albumin (R >0.446).

Conclusions

Children with trisomy 21 in this study have reduced lymphocyte bioenergetics. The clinical importance of this finding requires further studies.