High Glucose Alters Endoplasmic Reticulum Ca²⁺ Stores in T Lymphocytes Revealing Potential Novel Therapeutic Targets for Diabetic-Induced Immune Dysfunction

The objective of this study was to examine the effects of high glucose stress on endoplasmic reticulum (ER) Ca 2+ stores in T lymphocytes. Our hypothesis is that T lymphocytes exposed to chronic high glucose undergo an ER “stress” response due to impairment of Sarcoplasmic/endoplasmic reticulum Ca 2+ -ATPase (SERCA) pump-mediated Ca 2+ transport and dysregulated T cell ER Ca 2+ signaling. To examine ER Ca 2+ signaling events we conducted both intact and permeabilized cell Ca 2+ assays using Ca 2+ sensitive fluorescence dyes. Western Blot and RT-qPCR experiments were performed to detect SERCA expression levels. Our study found: 1. Incubation of T cells for an “early” phase (7-10 days) in high glucose resulted in differential changes in the SERCA 2b and SERCA 3 regulated Ca 2+ stores, as revealed by our specific Ca 2+ release protocol using thapsigargin and 2,5-di-( tert-butyl)-1,4-hydroquinone SERCA inhibition. 2. The early phase high glucose exposure increases Ca 2+ release from the SERCA 2b-regulated Ca 2+ pool whereas no change is observed in the SERCA 3-regulated pool. 3. We observed an increase in SERCA 2b expression levels during the early phase high glucose exposure but no change in SERCA 3 expression. 4. Long term high glucose exposure (>11 days) resulted in the loss of the augmented Ca 2+ release response from SERCA 2b sensitive Ca 2+ stores. 5. Treatment of T cells with the SERCA activator CDN1163 restored the augmented Ca 2+ release response from the SERCA 2b store. 6. Treatment of T cells in the ER stress phase with the chemical chaperone TUDCA protected T cells from high glucose induced loss in viability. Summary: High glucose exposure (as an in vitro mimic of a diabetic hyperglycemia state) perturbs ER Ca 2+ stores in T lymphocytes resulting in increased expression of SERCA 2b and augmented Ca 2+ storage whereas no apparent change is observable in the SERCA 3 Ca 2+ pool. Longer-term high glucose exposure results in the loss of the augmented SERCA 2b-sensitive store response, yet pharmacological SERCA 2b activation was able to restore enhanced Ca 2+ release from this pool. Conclusion: Our results are consistent with our hypothesis that high glucose exposure imposes a stress condition on T cell ER Ca 2+ stores with changes in SERCA-mediated Ca 2+ uptake activity. The findings in this study reveal an intriguing differential effect with the SERCA 2b pump isoform targeted for increased expression and augmented Ca 2+ storage whereas the SERCA 3-regulated Ca 2+ pools appear unaffected. Our experiments with the SERCA activator CDN1163 suggest a potential novel strategy to restore critical ER Ca 2+ signaling and T lymphocyte function in patients suffering from diabetic hyperglycemia. This work was supported by a SEED grant from the Jie Du Center, University of the Pacific. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.