1. IA-2 and IA-2 are proteins that belong to the family of tyrosine phosphatases without having phosphatase activity. In addition, both proteins were found to be major autoantigens in Type 1 diabetes. IA-2 and IA-2 are transmembrane proteins located in dense core and synaptic vesicles. Their deletion results in impaired secretion of hormones and neurotransmitters, and this results in a variety of abnormalities including impaired glucose tolerance, female infertility and behavior and learning disorders. Since the secretion of neurotransmitters are essential for the coordinated firing and synchronization of neurons in the suprachiasmatic nucleus, the primary CNS center for the generation of circadian rhythms, we have performed a series of experiments to see if the knockout of these two genes would result in abnormalities in circadian rhythmicity. Using radiotelemetry we determined 24 hour patterns of blood pressure, heart rate, temperature and spontaneous physical activity under standard lighting conditions (12 hours dark/12 hours light). Targeted deletion of both IA-2 and IA-2 profoundly disrupted the usual diurnal variation associated with each of these functions. Blood pressure was found to be locked at the low levels normally seen in the inactive daytime period. Exposure of animals to 24 hour darkness did not re-establish blood pressure or heart rate rhythms. Absence of blood pressure rhythms was not due to impaired visual input since papillary reflexes to light exposure were found to be normal in the knockout mice. Neither the deletion of IA-2 or IA-2 alone, however, was sufficient to produce a major change in the diurnal rhythm although for currently unknown reasons IA-2-deficient mice had a significant reduction of blood pressure. In situ hybridization revealed that IA-2 and IA-2 are highly expressed in the suprachiasmatic nucleus, but their mRNA expression does not cycle in a circadian pattern. Given that IA-2 proteins are known regulators of exocytosis and transmitter release one may conclude that IA-2 and IA-2, proteins unrelated to members of the clock gene family, influence the secretion of neurotransmitters that are responsible for the synchronization among suprachiasmatic neurons. 2. The -adrenergic pathway has been considered to be an important potential effector of circadian variations in arterial blood pressure. Experiments were performed in 1/2-adrenergic receptor-deficient mice to assess whether this pathway is required for circadian variation in mean arterial pressure (MAP) and heart rate and to determine the impact of its loss on the response to changes in dietary salt. Twenty-four hour recordings of MAP, heart rate (HR) and locomotor activity were made in conscious 8-12 week old mice by radiotelemetry. Both WT and 1/2-adrenergic receptor-deficient mice demonstrated robust circadian variation in MAP and HR. However, 24 hour mean arterial blood pressure was significantly lower (102.02 1.81 vs. 92.11 2.62 mm Hg) in 1/2-deficient than wild type mice, heart rate was 16% lower, and day-night differences were reduced. Both WT and 1/2-deficient animals adapted to changed salt intake without a change of blood pressure. However, the 1/2 knockout mice demonstrated a striking reduction in locomotor activity in light and dark phases of the day. In WT, MAP was markedly affected by locomotor activity, resulting in bimodal distributions in both light and dark. When MAP was analyzed using only intervals without locomotor activity, bimodality and circadian differences were reduced, and there was no significant difference between the two genotypes. The results indicate that there is no direct effector role for the -adrenergic system in circadian variation of arterial pressure in mice, aside from the indirect consequences of altered locomotor activity. Our results also confirm that locomotor activity contributes strongly to circadian variation in BP in mice. We have also performed experiments to assess voluntary locomotor activity using cages equipped with running wheels. These studies have confirmed that wheel running activity is reduced in the absence of 1/2 receptors, but that circadian differences are maintained.
| Kim, Soo Mi; Theilig, Franziska; Qin, Yan et al. (2009) Dense-core vesicle proteins IA-2 and IA-2{beta} affect renin synthesis and secretion through the {beta}-adrenergic pathway. Am J Physiol Renal Physiol 296:F382-9 |
| Kim, Soo Mi; Power, Andrea; Brown, Timothy M et al. (2009) Deletion of the secretory vesicle proteins IA-2 and IA-2beta disrupts circadian rhythms of cardiovascular and physical activity. FASEB J 23:3226-32 |
| Wang, Ningning; Yang, Guangrui; Jia, Zhanjun et al. (2008) Vascular PPARgamma controls circadian variation in blood pressure and heart rate through Bmal1. Cell Metab 8:482-91 |
| Kim, Soo Mi; Huang, Yuning; Qin, Yan et al. (2008) Persistence of circadian variation in arterial blood pressure in beta1/beta2-adrenergic receptor-deficient mice. Am J Physiol Regul Integr Comp Physiol 294:R1427-34 |
