Effect of Epigallocatechin-3-gallate on Skeletal and Cognitive Phenotypes in a Down Syndrome Mouse Model

Abstract

Down syndrome (DS), a genetic disorder that affects ~1 in 700 live births, is caused by trisomy of human chromosome 21 (Hsa21). Individuals with DS are affected by a wide spectrum of phenotypes which vary in severity and penetrance. However, cognitive and skeletal impairments can be commonly observed in all individuals with DS. To study these phenotypes, we utilized the Ts65Dn mouse model that carries three copies of approximately half the gene orthologs found on Hsa21 and exhibit similar phenotypes as observed in humans with DS. Individuals with DS and Ts65Dn mice have deficits in bone mineral density (BMD), bone architecture, bone strength, learning and memory. Over-expression of DYRK1A, a serine-threonine kinase encoded on Hsa21, has been linked to deficiencies in DS bone homeostasis and cognition. Epigallocatechin-3-gallate (EGCG), an aromatic polyphenol found in high concentrations in green tea, is a selective inhibitor of DYRK1A activity. Normalization of DYRK1A activity by EGCG therefore may have the potential to ameliorate skeletal and cognitive deficits. We hypothesized that supplements containing EGCG obtained from health food stores/ online vendors will not be as effective as EGCG from a chemical company in correcting bone deficits associated with DS. Our results suggest that EGCG improves the bone mineral density of trisomic femurs significantly better than the supplements while the EGCgNOW supplement from NOW FOODS improves trabecular and cortical bone structure. The results from HPLC analysis of supplements showed the presence of other catechins in EGCgNOW and degradation analysis revealed the rapid degradation of supplements. Therefore we hypothesize that the presence of EGCG degradation products and other green tea catechins in supplements may play a role in the differential skeletal effects we observed. We further hypothesized that a three week treatment of adolescent mice with EGCG will lead to an improvement in the learning and memory deficits that are observed in trisomic animals in comparison to control mice. However, our results indicate that three weeks of low-dose EGCG treatment during adolescence is insufficient to improve hippocampal dependent learning and memory deficits of Ts65Dn mice. The possibility remains that a higher dose of EGCG that begins at three weeks but lasts throughout the behavioral test period may result in improvement in learning and memory deficit of Ts65Dn mice.