Rescue of Calcineurin Aα−/− Mice Reveals a Novel Role for the α Isoform in the Salivary Gland

Abstract

Calcineurin is an important signal transduction mediator in T cells, neurons, the heart, and kidneys. Recent evidence points to unique actions of the two main isoforms of the catalytic subunit. Although the β isoform is required for T-cell development, α is important in the brain and kidney. In addition, mice lacking α but not β suffer from failure to thrive and early mortality. The purpose of this study was to identify the cause of postnatal death of calcineurin α null (CnAα(-/-)) mice and to determine the mechanism of α activity that contributes to the phenotype. CnAα(-/-) mice and wild-type littermate controls were fed a modified diet and then salivary gland function and histology were examined. In vitro studies were performed to identify the mechanism of α action. Data show that calcineurin is required for normal submandibular gland function and secretion of digestive enzymes. Loss of α does not impair nuclear factor of activated T-cell activity or expression but results in impaired protein trafficking downstream of the inositol trisphosphate receptor. These findings show a novel function of calcineurin in digestion and protein trafficking. Significantly, these data also provide a mechanism to rescue to adulthood a valuable animal model of calcineurin inhibitor-mediated neuronal and renal toxicities.

Nutritional Intervention Restores Muscle but Not Kidney Phenotypes in Adult Calcineurin Aα Null Mice

“…Subsequently, we reported that CnAα−/− mice could be rescued by feeding them a modified diet. Null mice quickly regained weight comparable to littermates and maintained a normal body mass into adulthood [9]. These results make it clear that previous reports of CnAα functions were made in the setting malnutrition.…”

“…While CnAβ−/− mice have a normal body weight and are fertile, failure to thrive and early lethality of CnAα −/− mice has been noted by several groups including our own [3], [6]–[8]. Recently, we reported that loss of CnAα alters salivary gland function [9]. This finding was particularly significant because it suggested a possible way to intervene in the failure to thrive which was a predominant feature of null pups.…”

“…Mice in this study were rescued by supplemental feeding as previously described [9] with minor modifications (see Methods). CnAα−/− mice and wildtype (WT) littermates were provided a modified diet (MD) beginning at approximately 2 weeks of age; supplemental feeding with the MD was offered to all mice throughout the experiment.…”

“…All experiments were carried out with 6–8 week old littermates. Dietary supplementation consisted of previously reported methods [9] with some modifications. Briefly, 0.16 g of PancreVed Powder (Vedco, Encinitas, CA) was dissolved in 30 ml peanut oil and then 500 ul was applied to approximately 500 grams of moistened, standard rodent chow.…”

Calcineurin signaling in the heart: The importance of time and place

“…Transcript and protein levels for CnAβ, but not CnAα, increase in response to mechanical stress or hypertrophic agonists in a calcineurin-dependent fashion [10, 22, 23]. Mice lacking CnAα have a severely shortened life span, therefore, a rigorous analysis of their cardiovascular phenotype has not been undertaken [24–26]. The hearts of mice lacking CnAβ are smaller than wild type littermates and show reduced hypertrophy in response to pressure overload [27].…”