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 NFAT5͞TonEBP 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 NFAT5͞TonEBP transcriptional activity and hsp70.1 promoter function were completely eliminated, and cell proliferation under hyperosmotic culture conditions was markedly impaired. Partial loss of NFAT5͞TonEBP 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 NFAT5͞TonEBP osmotic stress response pathway in vivo.

Modulation of renal-specific oxidoreductase/ myo -inositol oxygenase by high-glucose ambience

“…Here, the question that needs to be addressed is how high-glucose ambience or hyperglycemia modulates that activity or expression. NFAT5 belongs to the family of transcription factors and is also known as OsREBP or tonicity-responsive-enhancer-binding protein (TonEBP) (28). Upon stimulation by hypertonicity and following phosphorylation, OsREBP and TonEBP rapidly translocate into the nucleus and bind to OsREs in the promoter region of osmoprotective genes to stimulate transcription.…”

“…NFAT5 is also known as OsREbinding protein (OsREBP) or tonicity-responsive-enhancerbinding protein, with consensus sequence of binding motif as: NGGAAAWDHMN (the minimal OsRE motif is underlined) (28). Minimal GGAAA motif was present at six positions in the mouse RSOR 5Ј flanking sequence (Table 1).…”

Downregulation of NFAT5 by RNA interference reduces monoclonal antibody productivity of hybridoma cells

“…NFAT5 is also necessary for optimal T-cell development in vivo and allows for optimal cell growth ex vivo under conditions associated with osmotic stress [27]. Furthermore, William Go and his co-workers [21,28] measured lymphoid tissue osmolality directly by using a vapor pressure osmometer and they found that in contrast to brain and lung, lymphoid tissues were significantly hypertonic relative to serum. These results suggested that NFAT5, the osmosensitive transcription factor, functions to optimize lymphocyte function in hypertonic lymphoid microenvironment.…”

“…The relevance of osmotic stress to the function of T cells or peripheral blood mononuclear cells was first demonstrated in ex vivo studies, showing that proliferation or cytokine production is enhanced upon culture in hypertonic medium [21][22][23]. In T cells, NFAT5 controls the osmotic stress-induced expression of several cytokines, including tumor-necrosis factor, interleukin-2, and lymphotoxin-β [24,25].…”

Impact of environmental factors on alloimmunity and transplant fate

“…NaCl is the main determinant of the extracellular fluid volume of the body and is tightly regulated by pressure receptors, the sympathetic nervous system, and hormones, including the renin-angiotensin-aldosterone system; however, recent studies have demonstrated that isotonicity is not stable in tissues. Lymphoid tissues were found to be hyperosmolar (2), and 23 Na MRI demonstrated greater sodium accumulation in the skin of patients with refractory hypertension (3). Macrophages appear to play a role in buffering excess salt intake, preventing expansion of the extracellular volume and consequently blunting surges in blood pressure.…”