Time knowledge impairments in children with ADHD

BACKGROUND

A large number of studies have shown time perception impairment and reaction time (RT) variability in children with attention deficit hyperactivity disorder (ADHD), and have discussed the causes of such difficulties. However, very few studies have investigated time knowledge (i.e., the correct representation and use of time units) in children with ADHD.

METHODS

We evaluated time knowledge in 33 children with ADHD, aged 8-12 years, who had consulted a reference center for learning disabilities in Paris, matched for age and gender with 33 typically developing (TD) children. We used a simple questionnaire-based survey and neuropsychological tests for cognitive and attentional skills.

RESULTS

The acquisition of time knowledge was delayed in children with ADHD compared with TD children (P<0.01). At the end of primary school, children with ADHD obtained time knowledge scores that were close to those of TD children at the beginning of primary school. In children with ADHD, time knowledge was significantly related to the working memory index (P<0.05), but not to ADHD presentation (with or without hyperactivity).

CONCLUSION

This study shows time knowledge impairment in children with ADHD, and paves the way for new screening tests and rehabilitation focused on time knowledge and time-related skills, in order to improve patient care and autonomy.

Confluence switch signaling regulates ECM composition and the plasmin proteolytic cascade in keratinocytes

In culture, cell confluence generates signals that commit actively growing keratinocytes to exit the cell cycle and differentiate to form a stratified epithelium. Using a comparative proteomic approach, we studied this 'confluence switch' and identified a new pathway triggered by cell confluence that regulates basement membrane (BM) protein composition by suppressing the uPA-uPAR-plasmin pathway. Indeed, confluence triggers adherens junction maturation and enhances TGF-β and activin A activity, resulting in increased deposition of PAI-1 and perlecan in the BM. Extracellular matrix (ECM)-accumulated PAI-1 suppresses the uPA-uPAR-plasmin pathway and further enhances perlecan deposition by inhibiting its plasmin-dependent proteolysis. We show that perlecan deposition in the ECM strengthens cell adhesion, inhibits keratinocyte motility and promotes additional accumulation of PAI-1 in the ECM at confluence. In agreement, during wound-healing, perlecan concentrates at the wound-margin, where BM matures to stabilize keratinocyte adhesion. Our results demonstrate that confluence-dependent signaling orchestrates not only growth inhibition and differentiation, but also controls ECM proteolysis and BM formation. These data suggest that uncontrolled integration of confluence-dependent signaling, might favor skin disorders, including tumorigenesis, not only by promoting cell hyperproliferation, but also by altering protease activity and deposition of ECM components.

Adipocyte differentiation of multipotent cells established from human adipose tissue

In this study multipotent adipose-derived stem cells isolated from human adipose tissue (hMADS cells) were shown to differentiate into adipose cells in serum-free, chemically defined medium. During the differentiation process, hMADS cells exhibited a gene expression pattern similar to that described for rodent clonal preadipocytes and human primary preadipocytes. Differentiated cells displayed the key features of human adipocytes, i.e., expression of specific molecular markers, lipolytic response to agonists of beta-adrenoreceptors (beta2-AR agonist > beta1-AR agonist >> beta3-AR agonist) and to the atrial natriuretic peptide, insulin-stimulated glucose transport, and secretion of leptin and adiponectin. hMADS cells were able to respond to drugs as inhibition of adipocyte differentiation was observed in the presence of prostaglandin F2alpha, tumour necrosis factor-alpha, and nordihydroguaiaretic acid, a natural polyhydroxyphenolic antioxidant. Thus, for the first time, human adipose cells with normal karyotype and indefinite life span have been established. They represent a novel and valuable tool for studies of fat tissue development and metabolism.