Repercussion of cAMP and EPAC in Memory and Signaling

It is well recognized that cyclic adenosine monophosphate (cAMP) signaling within neurons plays a key role in the foundation of long-term memories. Memory storage is the process that demands the movement of signals, neural plasticity, and the molecules which can transfer the signals from the sensory neuron to the dorsal root ganglion (DRG) neurons and later into the temporal region of the brain. The discovery of cAMP in 1958 as the second messenger also had a role in memory formation and other neural aspects. Further, in 1998 the scientists found that cAMP does not just activate protein kinase A (PKA) but also exchange protein directly activated by cAMP (Epac) which has an active role to play in hyperalgesia, memory, and signaling. The cAMP has three targets, hyperpolarization-activated cyclic nucleotide modulated (HCN) channels, protein kinase A (PKA), and exchange protein activated by cAMP (Epac). Different research has exposed that both PKA and HCN channels are significant for long-term memory creation. Epac is a cAMP-dependent guanine nucleotide exchange factor for the small G proteins including Rap1. However, slight information is there about the role of Epac in this process. The effects of cAMP are predominantly imparted by activating protein kinase A (PKA) and the more newly discovered exchange proteins are directly activated by cAMP 1 and 2 (EPAC1 and EPAC2). This review provides an insight regarding the function and role of both of these secondary messengers in memory and nerve signaling.

Exchange Protein Directly Activated by cAMP 2 Enhances Respiratory Syncytial Virus-Induced Pulmonary Disease in Mice

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection in young children. It is also a significant contributor to upper respiratory tract infections, therefore, a major cause for visits to the pediatrician. High morbidity and mortality are associated with high-risk populations including premature infants, the elderly, and the immunocompromised. However, no effective and specific treatment is available. Recently, we discovered that an exchange protein directly activated by cyclic AMP 2 (EPAC2) can serve as a potential therapeutic target for RSV. In both lower and upper epithelial cells, EPAC2 promotes RSV replication and pro-inflammatory cytokine/chemokine induction. However, the overall role of EPAC2 in the pulmonary responses to RSV has not been investigated. Herein, we found that EPAC2-deficient mice (KO) or mice treated with an EPAC2-specific inhibitor showed a significant decrease in body weight loss, airway hyperresponsiveness, and pulmonary inflammation, compared with wild-type (WT) or vehicle-treated mice. Overall, this study demonstrates the critical contribution of the EPAC2-mediated pathway to airway diseases in experimental RSV infection, suggesting the possibility to target EPAC2 as a promising treatment modality for RSV.

Molecular Identification of Anion Exchange Protein 3 in Pacific White Shrimp (Litopenaeus vannamei): mRNA Profiles for Tissues, Ontogeny, Molting, and Ovarian Development and Its Potential Role in Stress-Induced Gill Damage

Bicarbonate (HCO3–) transport mechanisms play an essential role in the acid-base homeostasis of aquatic animals, and anion exchange protein 3 (AE3) is a membrane transport protein that exchanges Cl–/HCO3– across the cell membrane to regulate the intracellular pH. In this study, the full-length cDNA of AE3 (Lv-AE3) was obtained from the Pacific white shrimp (Litopenaeus vannamei). The Lv-AE3 cDNA is 4,943 bp in length, contains an open reading frame of 2,850 bp, coding for a protein of 949 amino acids with 12 transmembrane domains. Lv-AE3 shows high sequence homology with other AE3 at the protein level. Lv-AE3 mRNA was ubiquitously detected in all tissues selected, with the highest expression level in the gill, followed by the ovary, eyestalk and brain. By in situ hybridization, Lv-AE3-positive cells were shown predominant localization in the secondary gill filaments. The expression levels of Lv-AE3 were further investigated during the essential life processes of shrimp, including ontogeny, molting, and ovarian development. In this case, the spatiotemporal expression profiles of Lv-AE3 in L. vannamei were highly correlated with the activities of water and ion absorption; for example, increased mRNA levels were present after hatching, during embryonic development, after ecdysis during the molt cycle, and in the stage IV ovary during gonadal development. After low/high pH and low/high salinity challenges, the transcript levels of Lv-AE3 were reduced in the gill, while the cell apoptosis rate increased. In addition, knockdown of Lv-AE3 mRNA expression induced cell apoptosis in the gill, indicating a potential link between Lv-AE3 and gill damage. Altogether, this study thoroughly investigated the relationship between the mRNA expression profiles of Lv-AE3 and multiple developmental and physiological processes in L. vannamei, and it may benefit the protection of crustaceans from fluctuated aquatic environments.

Broad Impact of Exchange Protein Directly Activated by cAMP 2 (EPAC2) on Respiratory Viral Infections

The recently discovered exchange protein directly activated by cAMP (EPAC), compared with protein kinase A (PKA), is a fairly new family of cAMP effectors. Soon after the discovery, EPAC has shown its significance in many diseases including its emerging role in infectious diseases. In a recent study, we demonstrated that EPAC, but not PKA, is a promising therapeutic target to regulate respiratory syncytial virus (RSV) replication and its associated inflammation. In mammals, there are two isoforms of EPAC—EPAC1 and EPAC2. Unlike other viruses, including Middle East respiratory syndrome coronavirus (MERS-CoV) and Ebola virus, which use EPAC1 to regulate viral replication, RSV uses EPAC2 to control its replication and associated cytokine/chemokine responses. To determine whether EPAC2 protein has a broad impact on other respiratory viral infections, we used an EPAC2-specific inhibitor, MAY0132, to examine the functions of EPAC2 in human metapneumovirus (HMPV) and adenovirus (AdV) infections. HMPV is a negative-sense single-stranded RNA virus belonging to the family Pneumoviridae, which also includes RSV, while AdV is a double-stranded DNA virus. Treatment with an EPAC1-specific inhibitor was also included to investigate the impact of EPAC1 on these two viruses. We found that the replication of HMPV, AdV, and RSV and the viral-induced immune mediators are significantly impaired by MAY0132, while an EPAC1-specific inhibitor, CE3F4, does not impact or slightly impacts, demonstrating that EPAC2 could serve as a novel common therapeutic target to control these viruses, all of which do not have effective treatment and prevention strategies.

Energy metabolism in aberdeen-angus bulls during the growing period with different levels of metabolizable protein in the diets

The nature of biosynthetic processes and the productive qualities of ruminants depend on the level and ratio of substrates absorbed in the digestive tract. The maximum efficiency of the biosynthesis of meat components in the body is ensured if the amino acids enter the metabolic pool in sufficient quantity and in the optimal ratio. The purpose of the work is to study the needs of Aberdeen Angus meat bulls calves for metabolizable protein for the optimal use of amino acids and metabolizable energy of the diet for the increase in live weight of bulls-calves during the growing period. Research materials. Consecutively, 3 series of studies were carried out on bulls calves of the Aberdeen Angus breed with a live weight of 277 kg, 317 kg and 363 kg. The animals of the 1st experiment were fed according to the RAAS (Russian Academy of Agricultural Sciences) standards, where the ratio of the exchange protein to the exchange energy was 8.2 g/MJ, in the 2nd and 3rd experiments they increased the level of the exchange protein to 8.6 and 9.1 g/MJ due to the introduction of 0.5 kg and 0.6 kg of soybean meal in the diet, respectively. At the end of each period, physiological experiments were performed. Results. The studied parameter did not have a significant effect on the dry matter intake of the feed, and an increase in the diet of hard-to-break down protein contributed to an increase in the concentration of metabolizable energy and digestibility of dry matter. It was found that metabolizable energy and amino acids are effectively used to increase the live weight of bulls calves during the growing period on a diet in which the ratio of metabolizable protein to metabolizable energy is 8.6 g/MJ. A further increase in metabolic protein in the diet leads to an increase in heat production, which in turn increases the use of amino acids and metabolic energy in energy metabolism and reduces their contribution to the increase in live weight.

External α-carbonic anhydrase and solute carrier 4 are required for bicarbonate uptake in a freshwater angiosperm

The freshwater monocot Ottelia alismoides is the only known species to operate three CO2-concentrating mechanisms (CCMs): constitutive bicarbonate (HCO3–) use, C4 photosynthesis, and facultative Crassulacean acid metabolism, but the mechanism of HCO3– use is unknown. We found that the inhibitor of an anion exchange protein, 4,4'-diisothio-cyanatostilbene-2,2'-disulfonate (DIDS), prevented HCO3– use but also had a small effect on CO2 uptake. An inhibitor of external carbonic anhydrase (CA), acetazolamide (AZ), reduced the affinity for CO2 uptake but also prevented HCO3– use via an effect on the anion exchange protein. Analysis of mRNA transcripts identified a homologue of solute carrier 4 (SLC4) responsible for HCO3– transport, likely to be the target of DIDS, and a periplasmic α-carbonic anhydrase 1 (α-CA1). A model to quantify the contribution of the three different pathways involved in inorganic carbon uptake showed that passive CO2 diffusion dominates inorganic carbon uptake at high CO2 concentrations. However, as CO2 concentrations fall, two other pathways become predominant: conversion of HCO3– to CO2 at the plasmalemma by α-CA1 and transport of HCO3– across the plasmalemma by SLC4. These mechanisms allow access to a much larger proportion of the inorganic carbon pool and continued photosynthesis during periods of strong carbon depletion in productive ecosystems.