Dynamic expression of aquaporins in physiological and pathophysiological in vitro models.

Abstract

Water is the main component of biological fluids and a prerequisite of all organisms living. In 1987, Agre isolated a new integral membrane protein acting as a channel that mediates the water flux and uncharged solutes across biological membranes. This protein was called aquaporin1 and ever since its discovery, more than 300 homologues have been identified in animal, bacteria and plant. In human have been discovered 13 aquaporins (AQPs) isoform (AQP0-AQP12) widely distributed in various epithelia and endothelia where are important actors of fluid homeostasis in secretory and absorptive processes in response to an osmotic or pressure gradient. In the human brain nine aquaporin subtypes (AQP1, 2, 3, 4, 5, 7, 8, 9, and 11) have been recognized and partially characterized, but only three aquaporins (AQP1, 4, and 9) have been clearly identified in vivo. This discovery highlighted the concept of the important role of AQPs in all brain functions and of the dynamics of water molecules in the cerebral cortex. Additionally, AQPs relieved an important role in glial control and neuronal excitability, such as in brain structure and general development. However, a clearer understanding of specific function and distribution of water channels in adult or in development brain requires a more detailed elucidation. Some of these findings are limited from the complexity of direct investigation, inaccessibility of the neural tissue, and hence difficulty in obtaining a brain biopsy, until after the death of an individual. In this sense, several past and present in vitro models have been used to provide important clues about many processes, such as brain development, neurotoxicity, inflammation, pathogenic mechanisms of the diseases and potential pharmacological targets. In the Chapter I, we have reviewed some in vitro approaches used to investigate the mechanisms involved in Krabbe disease with particular regard to the cellular systems employed to study processes of inflammation, apoptosis and angiogenesis. In this study, we used some in vitro methods with the aim to update the knowledge on stem cells biology and to provide a relationship between aquaporins expression and cellular differentiation. In particular, we have analysed the differentiation of human mesenchymal stem cells from adipose tissue (AT-MSCs) into neural phenotypes and SH-SY5Y neuroblastoma cell line into physiological and pathophysiological dopaminergic neurons. In the Chapter II, we have reported the results of the expression of AQP1, 4, 7, 8 and 9 at 0, 14, and 28 days in AT-MSCs during the neural differentiation by immunocytochemistry, RT-PCR and Western blot analysis. Our studies demonstrated that AT-MSCs could be differentiated into neurons, astrocytes and oligodendrocytes, showing reactivity not only for the typical neural markers, but also for specific AQPs in dependence from differentiated cell type. Our data revealed that at 28 days AT-MSCs express AQP1, astrocytes AQP1, 4 and 7, oligodendrocytes AQP1, 4 and 8, and finally neurons AQP1 and 7. In the Chapter III, we have examined the possible involvement of AQPs in a Parkinson s disease-like cell model. For this purpose, we used SH-SY5Y cell line, differentiated in dopaminergic neurons with retinoic acid (RA) and phorbol 12-myristate 13-acetate (MPA) alone or in association. The vulnerability to dopaminergic neurotoxin 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) and H2O2 was evaluated and compared in all cell groups. We found that the vulnerability of cells was linked to dynamic changes of AQP4 and AQP9. The data described here provides fundamental insights on the biology of the human mesenchymal stem cells and significant evidences on the involvement of AQPs in a variety of physiological and pathophysiological processes. This suggests their possible application as markers, which may be helpful in diagnosing as well as in the understanding of neurodegenerative diseases for future therapeutic approaches.