P0011THE ROLE OF AQUAPORIN-11 (AQP11) IN THE THYMUS DEVELOPMENT

Abstract

Abstract Background and Aims Some aquaporins transport not only water but also small non-ionic molecules such as glycerol. In fact, aquaporin-9 (AQP9) has been shown to transport glycerol which is critical to support memory T cell survival through metabolic fitness (Cui G et al. Cell. 161:750, 2015). As AQP11 is widely expressed and transport glycerol as well as water, AQP11 may also play a role in immunological system, which will expand the repertoire of the aquaporin research field. Method The AQP11 expression in the thymus was examined by RT-PCR, Western blot and immunohistochemistry in mice. Phenotypic analysis and microarray analysis of the thymus were conducted in wild and AQP11 null mice at 21 day old before the development of uremia due to polycystic kidneys. Results Both mRNA and protein expressions of AQP11 in the thymus were higher than those of the kidney by RT-PCR and Western blot. Interestingly, the size of the thymus from AQP11 null mice was smaller than that of the wild mice: 28mg vs. 56mg, even after the correction by the body weight: 0.59 % vs. 0.82 %, as the body size of AQP11 null mice was smaller. The vacuolated medullary epithelial cells were observed in the thymus of AQP11 null mice with narrowed cortex. The immunohistochemical analysis revealed the AQP11 expression at the stromal-epithelial cells in the thymus. The microarray analysis of the gene expression in the thymus was compared between the wild and AQP11 null thymus by the annotation analysis based on the David Bioinformatics Resources 6.8 (beta). The up-regulated 66 genes more than 1.5 folds in AQP11 null thymus are mainly related to the PI3K/Akt signaling pathway to promote metabolism, proliferation, cell survival, growth and angiogenesis. On the other hand, the down-regulated 55 genes less than half in AQP11 null thymus are related to energy production and the peroxisome proliferator-activated receptor (PPAR) signaling pathway. Further RT-qPCR analysis confirmed the enhanced expression of Egfr (Epidermal Growth Factor Receptor), Itgb4 (Integrin beta-4) and Il2ra (interleukin 2 receptor alpha) and the diminished expression of aquaglyceroporin AQP7, Pck1 (Phosphoenolpyruvate carboxy-kinase 1) and Ucp1 (Mitochondrial uncoupling protein 1). The up-regulated genes for growth signaling was unexpected with the smaller thymus but may support the survival of the hypoplastic thymus as a compensation. On the other hand, the down-regulated genes may compromise fat-glucose-energy metabolism in the thymus leading to the smaller thymus, which may be aggravated by the decreased expression of AQP7, another glycerol channel. Conclusion AQP11 may play an important role in the metabolic control of the developing thymus possibly through its glycerol transport. The smaller thymus with narrower cortex in AQP11 null mice may lead to immunological dysfunction, which is currently under study.