Expression of ZAKI-4 messenger ribonucleic acid in the brain during rat development and the effect of hypothyroidism

The scale of zebrafish pectoral fin buds is determined by intercellular K+ levels and consequent Ca2+-mediated signaling via retinoic acid regulation of Rcan2 and Kcnk5b

K+ channels regulate morphogens to scale adult fins, but little is known about what regulates the channels and how they control morphogen expression. Using the zebrafish pectoral fin bud as a model for early vertebrate fin/limb development, we found that K+ channels also scale this anatomical structure, and we determined how one K+-leak channel, Kcnk5b, integrates into its developmental program. From FLIM measurements of a Förster Resonance Energy Transfer (FRET)-based K+ sensor, we observed coordinated decreases in intracellular K+ levels during bud growth, and overexpression of K+-leak channels in vivo coordinately increased bud proportions. Retinoic acid, which can enhance fin/limb bud growth, decreased K+ in bud tissues and up-regulated regulator of calcineurin (rcan2). rcan2 overexpression increased bud growth and decreased K+, while CRISPR-Cas9 targeting of rcan2 decreased growth and increased K+. We observed similar results in the adult caudal fins. Moreover, CRISPR targeting of Kcnk5b revealed that Rcan2-mediated growth was dependent on the Kcnk5b. We also found that Kcnk5b enhanced depolarization in fin bud cells via Na+ channels and that this enhanced depolarization was required for Kcnk5b-enhanced growth. Lastly, Kcnk5b-induced shha transcription and bud growth required IP3R-mediated Ca2+ release and CaMKK activity. Thus, we provide a mechanism for how retinoic acid via rcan2 can regulate K+-channel activity to scale a vertebrate appendage via intercellular Ca2+ signaling.

Elevated Serum Regulator of Calcineurin 2 is Associated With an Increased Risk of Non-Alcoholic Fatty Liver Disease

Background: The promoting effect of the regulator of calcineurin 2 (RCAN2) in hepatic steatosis has been observed in animal studies. However, the association of RCAN2 with non-alcoholic fatty liver disease (NAFLD) in humans remains unclear. This study aimed to evaluate the expression of RCAN2 in the liver of mice with hepatic steatosis and in the serum of NAFLD patients and to explore the relationship between serum RCAN2 levels and NAFLD.

Methods: The mRNA and protein expression of RCAN2 were detected by quantitative real-time PCR (qRT-PCR) and Western blot. NAFLD was diagnosed by abdominal ultrasonography. Circulating RCAN2 levels were measured by ELISA kits. The relationship between serum RCAN2 levels and NAFLD was assessed.

Results: qRT-PCR and Western blot analysis showed that compared with the corresponding controls, the mRNA and protein expression of RCAN2 were significantly increased in the liver tissues of db/db and mice on a high-fat diet. Serum RCAN2 levels were markedly elevated in NAFLD patients compared with non-NAFLD subjects. Binary logistic regression analysis showed that serum RCAN2 levels were significantly associated with NAFLD. Receiver operation characteristic (ROC) curve analysis showed that serum RCAN2 might act as a predictive biomarker for NAFLD [area under the curve (AUC) = 0.663, 95% CI = 0.623–0.702], and the serum RCAN2/(AST/ALT) ratio displayed improved predictive accuracy (AUC = 0.816, 95% CI = 0.785–0.846).

Conclusion: Elevated serum RCAN2 levels were associated with an increased risk of NAFLD. Serum RCAN2, especially the serum RCAN2/(AST/ALT) ratio, might be a candidate diagnostic marker for NAFLD.

Association Between Circulating Regulator of Calcineurin 2 Concentrations With Overweight and Obesity

BACKGROUND

Regulator of calcineurin 2 (RCAN2) has been reported to promote food intake and weight gain in animal studies. However, its effect on body weight in humans is unclear.

OBJECTIVE

This study aimed to investigate the relationship between serum RCAN2 concentrations and participants with overweight/obesity.

METHODS

A cross-sectional study was performed in 872 Chinese adults, including 348 participants with normal weight (NW), 397 participants with overweight (OW), and 127 participants with obesity (OB). All participants were divided into NW, OW and OB groups according to their body mass index (BMI). Serum RCAN2 concentrations were determined by enzyme-linked immunosorbent assay.

RESULTS

Serum RCAN2 concentrations gradually increased with the increase of BMI (p < 0.001). The percentages of OW/OB gradually increased in tandem with increasing tertiles of RCAN2 (p < 0.001). Additionally, serum RCAN2 concentrations were significantly correlated with a series of anthropometric and metabolic parameters, predominantly including body weight, BMI, SBP, DBP, total cholesterol, triglycerides, HDL-C, LDL-C (all p < 0.05). Furthermore, logistic regression analysis showed that the risk of OW/OB was significantly increased with the increase of serum RCAN2 concentrations. Receiver operation characteristic (ROC) curve analysis revealed that serum RCAN2, especially serum RCAN2/(AST/ALT) ratio, might serve as a candidate biomarker for obesity.

CONCLUSION

Serum RCAN2 concentrations were increased in subjects with OW/OB. The increased serum RCAN2 concentrations were associated with the increased risks of OW/OB.

Regulator of Calcineurin (RCAN): Beyond Down Syndrome Critical Region

The regulator of calcineurin (RCAN) was first reported as a novel gene called DSCR1, encoded in a region termed the Down syndrome critical region (DSCR) of human chromosome 21. Genome sequence comparisons across species using bioinformatics revealed three members of the RCAN gene family, RCAN1, RCAN2, and RCAN3, present in most jawed vertebrates, with one member observed in most invertebrates and fungi. RCAN is most highly expressed in brain and striated muscles, but expression has been reported in many other tissues, as well, including the heart and kidneys. Expression levels of RCAN homologs are responsive to external stressors such as reactive oxygen species, Ca2+, amyloid β, and hormonal changes and upregulated in pathological conditions, including Alzheimer's disease, cardiac hypertrophy, diabetes, and degenerative neuropathy. RCAN binding to calcineurin, a Ca2+/calmodulin-dependent phosphatase, inhibits calcineurin activity, thereby regulating different physiological events via dephosphorylation of important substrates. Novel functions of RCANs have recently emerged, indicating involvement in mitochondria homeostasis, RNA binding, circadian rhythms, obesity, and thermogenesis, some of which are calcineurin-independent. These developments suggest that besides significant contributions to DS pathologies and calcineurin regulation, RCAN is an important participant across physiological systems, suggesting it as a favorable therapeutic target.

Distinct Functional Groups Emerge from the Intrinsic Properties of Molecularly Identified Entorhinal Interneurons and Principal Cells

Inhibitory interneurons are an important source of synaptic inputs that may contribute to network mechanisms for coding of spatial location by entorhinal cortex (EC). The intrinsic properties of inhibitory interneurons in the EC of the mouse are mostly undescribed. Intrinsic properties were recorded from known cell types, such as, stellate and pyramidal cells and 6 classes of molecularly identified interneurons (regulator of calcineurin 2, somatostatin, serotonin receptor 3a, neuropeptide Y neurogliaform (NGF), neuropeptide Y non-NGF, and vasoactive intestinal protein) in acute brain slices. We report a broad physiological diversity between and within cell classes. We also found differences in the ability to produce postinhibitory rebound spikes and in the frequency and amplitude of incoming EPSPs. To understand the source of this intrinsic variability we applied hierarchical cluster analysis to functionally classify neurons. These analyses revealed physiologically derived cell types in EC that mostly corresponded to the lines identified by biomarkers with a few unexpected and important differences. Finally, we reduced the complex multidimensional space of intrinsic properties to the most salient five that predicted the cellular biomolecular identity with 81.4% accuracy. These results provide a framework for the classification of functional subtypes of cortical neurons by their intrinsic membrane properties.

Selective functional interactions between excitatory and inhibitory cortical neurons and differential contribution to persistent activity of the slow oscillation

The neocortex depends upon a relative balance of recurrent excitation and inhibition for its operation. During spontaneous Up states, cortical pyramidal cells receive proportional barrages of excitatory and inhibitory synaptic potentials. Many of these synaptic potentials arise from the activity of nearby neurons, although the identity of these cells is relatively unknown, especially for those underlying the generation of inhibitory synaptic events. To address these fundamental questions, we developed an in vitro submerged slice preparation of the mouse entorhinal cortex that generates robust and regular spontaneous recurrent network activity in the form of the slow oscillation. By performing whole-cell recordings from multiple cell types identified with green fluorescent protein expression and electrophysiological and/or morphological properties, we show that distinct functional subpopulations of neurons exist in the entorhinal cortex, with large variations in contribution to the generation of balanced excitation and inhibition during the slow oscillation. The most active neurons during the slow oscillation are excitatory pyramidal and inhibitory fast spiking interneurons, receiving robust barrages of both excitatory and inhibitory synaptic potentials. Weak action potential activity was observed in stellate excitatory neurons and somatostatin-containing interneurons. In contrast, interneurons containing neuropeptide Y, vasoactive intestinal peptide, or the 5-hydroxytryptamine (serotonin) 3a receptor, were silent. Our data demonstrate remarkable functional specificity in the interactions between different excitatory and inhibitory cortical neuronal subtypes, and suggest that it is the large recurrent interaction between pyramidal neurons and fast spiking interneurons that is responsible for the generation of persistent activity that characterizes the depolarized states of the cortex.

Mice lacking the calcineurin inhibitor Rcan2 have an isolated defect of osteoblast function

Calcineurin-nuclear factor of activated T cells signaling controls the differentiation and function of osteoclasts and osteoblasts, and regulator of calcineurin-2 (Rcan2) is a physiological inhibitor of this pathway. Rcan2 expression is regulated by T(3), which also has a central role in skeletal development and bone turnover. To investigate the role of Rcan2 in bone development and maintenance, we characterized Rcan2(-/-) mice and determined its skeletal expression in T(3) receptor (TR) knockout and thyroid-manipulated mice. Rcan2(-/-) mice had normal linear growth but displayed delayed intramembranous ossification, impaired cortical bone formation, and reduced bone mineral accrual during development as well as increased mineralization of adult bone. These abnormalities resulted from an isolated defect in osteoblast function and are similar to skeletal phenotypes of mice lacking the type 2 deiodinase thyroid hormone activating enzyme or with dominant-negative mutations of TRα, the predominant TR isoform in bone. Rcan2 mRNA was expressed in primary osteoclasts and osteoblasts, and its expression in bone was differentially regulated in TRα and TRβ knockout and thyroid-manipulated mice. However, in primary osteoblast cultures, T(3) treatment did not affect Rcan2 mRNA expression or nuclear factor of activated T cells c1 expression and phosphorylation. Overall, these studies establish that Rcan2 regulates osteoblast function and its expression in bone is regulated by thyroid status in vivo.

Differential expression of members of the RCAN family of calcineurin regulators suggests selective functions for these proteins in the brain

RCANs, also called Down Syndrome Critical Region-1 (DSCR1)-like proteins, Modulatory Calcineurin Interacting Proteins (MCIPs) or calcipressins, are regulators of calcineurin, a Ca(2+)-dependent protein phosphatase involved in several neuronal functions. Despite the potential importance of the RCAN proteins in brain physiology, very little is known about their relative abundance and distribution patterns in the central nervous system. In this study we report the expression and distribution of RCAN mRNA transcripts and proteins in the mouse brain. RT-PCR and Western blot analysis showed that all Rcan mRNAs (Rcan1-1, Rcan1-2, Rcan2-1, Rcan2-3 and Rcan3) and their corresponding protein products (RCAN1-L, RCAN1-S, RCAN2-L, RCAN2-S and RCAN3) are present in every adult mouse brain region examined. All protein isoforms are also expressed in these same brain regions at early postnatal stages. Within regions, RCAN1-L, RCAN1-S, RCAN2-L and RCAN3 are differentially expressed depending on the region and developmental stage, whereas RCAN2-S is distributed homogeneously. Detailed immunohistochemical analysis revealed significant differences in the cellular and subcellular distributions of RCAN proteins. In the adult, RCAN1 was mainly expressed in the neuropil throughout the brain. Although at lower levels, RCAN3 was also detected throughout the neuropil. In contrast, RCAN2 was highly expressed in scattered neurons, in both the nucleus and the cytoplasm. Interestingly, RCAN2 is the only member of the RCAN family that was detected in glial cells. Finally, the expression patterns of RCANs at early postnatal stages differed from those of the adult, in different brain areas, in both their distributions and relative abundance, suggesting that the expression of these proteins could be regulated during neuronal differentiation. The nonoverlapping expression patterns of the RCAN proteins shown here highlight the existence of different physiological scenarios and therefore suggest different RCAN functional activities in the brain, depending on the cellular context and developmental stage.

Calcineurin differentially regulates fast myosin heavy chain genes in oxidative muscle fibre type conversion

In skeletal muscle, calcineurin is crucial for myocyte differentiation and in the determination of the slow oxidative fibre phenotype, both processes being important determinants of muscle performance, metabolic health and meat-animal production. Fibre type is defined by the isoform identity of the skeletal myosin heavy chain (MyHC). We have examined the responses of the major MyHC genes to calcineurin signalling during fibre formation of muscle C2C12 cells. We have found that calcineurin acts as a signal to up-regulate the fast-oxidative MyHC2a gene and to down-regulate the faster MyHC2x and MyHC2b genes in a manner that appears to be NFAT-independent. Contrary to expectation, the up-regulation of MyHCslow by calcineurin seems to be time-dependent and is only detectable once the initial differential expression of the post-natal fast MyHC genes has been established. The simultaneous elevated expression of MyHC2a and the repression of MyHC2x and MyHC2b expression indicate that both processes (elevation and repression) are actively coordinated during oxidative fibre conversion. We have further determined that muscle LIM protein (MLP), a calcineurin-binding Z-line co-factor, is induced by calcineurin and that its co-expression with calcineurin has an additive effect on MyHCslow expression. Hence, post-natal fast MyHCs are important early effector targets of calcineurin, whereas MyHCslow up-regulation is mediated in part by calcineurin-induced MLP.

Thyroid hormone actions on neural cells

1. In addition to its role in cellular metabolic activity, thyroid hormone (TH) is critically involved in growth, development, and function of the central nervous system. In the brain, as in other structures, TH is described to exert its major action by the binding of L-3,5,3'-triiodothyronine (T3), considered as the bioactive form of the hormone, to nuclear thyroid hormone receptors (TR) that function as ligand-dependent transcription factors. 2. The transcription of numerous brain genes was indeed shown to be positively or negatively regulated by TH, turning these TR-mediated effects one explanation for the physiological effects of TH. In this context, the knowledge from TR-knockout studies provides some surprising results, since neonatal hypothyroidism is associated to more significant abnormalities than is TR deficiency. Some (nonexclusive) hypotheses include a permissive effect of TH, allowing derepression of unliganded-TR effects and non-TR-mediated effects of the hormone, further emphasizing the importance of a controlled accessibility of neural cells to TH. 3. On the other hand, T3 was demonstrated to directly act not only on neuronal but also on glial cells proliferation and differentiation, contributing to the harmonious development of the brain. Interestingly, in addition to these direct actions on neuronal and glial cells, several lines of evidence, notably developped in our laboratory, point out the role of thyroid hormone in neuronal-glial interactions.