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NFAT5/TonEBP mutant mice define osmotic stress as a critical feature of the lymphoid microenvironment.

ABSTRACT: Osmotic stress responses are critical not only to the survival of unicellular organisms but also to the normal function of the mammalian kidney. However, the extent to which cells outside the kidney rely on osmotic stress responses in vivo remains unknown. Nuclear factor of activated T cells 5 (NFAT5)/tonicity enhancer binding protein (TonEBP), the only known osmosensitive mammalian transcription factor, is expressed most abundantly in the thymus and is induced upon lymphocyte activation. Here we report that NFAT5/TonEBP is not only essential for normal cell proliferation under hyperosmotic conditions but also necessary for optimal adaptive immunity. Targeted deletion of exons 6 and 7 of the Nfat5 gene, which encode a critical region of the DNA-binding domain, gave rise to a complete loss of function in the homozygous state and a partial loss of function in the heterozygous state. Complete loss of function resulted in late gestational lethality. Furthermore, hypertonicity-induced NFAT5/TonEBP transcriptional activity and hsp70.1 promoter function were completely eliminated, and cell proliferation under hyperosmotic culture conditions was markedly impaired. Partial loss of NFAT5/TonEBP function resulted in lymphoid hypocellularity and impaired antigen-specific antibody responses in viable heterozygous animals. In addition, lymphocyte proliferation ex vivo was reduced under hypertonic, but not isotonic, culture conditions. Direct measurement of tissue osmolality further revealed lymphoid tissues to be hyperosmolar. These results indicate that lymphocyte-mediated immunity is contingent on adaptation to physiologic osmotic stress, thus providing insight into the lymphoid microenvironment and the importance of the NFAT5/TonEBP osmotic stress response pathway in vivo.

SUBMITTER: Go WY

PROVIDER: S-EPMC489993 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Macular edema, a frequently encountered complication of diabetic retinopathy (DR), results from alterations of the blood retinal barrier (BRB) and leads to modifications of the retinal pigmented epithelium (RPE) functions. Osmolar changes of the surrounding medium could be responsible for modifications of the RPE functions leading to disturbance of retinal homeostasis. The expression, activation and function of the key hyperosmolar response factor Tonicity Enhancer Binding Protein (TonEBP also called nuclear factor of activated T-cell 5 - NFTA5) was investigated in ARPE-19 cells, derived from human RPE, in response to hyperosmolar stimulation.ARPE-19 cells were exposed to hyperosmolar medium. TonEBP mRNA and protein levels were quantified by qRT-PCR and semi-quantitative Western blot. TonEBP nuclear translocation was investigated by immunofluorescence. TonEBP transactivation activity was measured using a reported plasmid containing TonEBP binding sites.In response to hyperosmolar stimulation of ARPE-19 cells, a dose-dependent increase in TonEBP mRNA and protein levels, as well as TonEBP nuclear translocation were observed. TonEBP transactivation activity was further demonstrated using a reporter plasmid containing TonEBP binding sites. A dominant negative form of TonEBP abolished NaCl-induced increase in TonEBP transactivation activity, and inhibited the increase of the target genes aldose reductase and sodium-dependent taurine transporter mRNA levels. SB203580, an inhibitor of two of the p38 protein kinase's isoforms (p38? and p38?) inhibited the TonEBP nuclear translocation and transactivation activity in ARPE-19 cells exposed to hyperosmolar stimulation.Our data demonstrates the involvement of TonEBP in the mechanisms responsible for osmoadaptation to hyperosmolar stress in RPE cells. Given the emerging role of TonEBP in different pathological pathways, these data open new perspectives for the analysis of the mechanisms involved in the modification of functions of the RPE during macular edema.

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NFAT5/TonEBP mutant mice define osmotic stress as a critical feature of the lymphoid microenvironment.

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