Mitogen-activated protein kinases contribute to temperature-induced cardiac remodelling in rainbow trout (Oncorhynchus mykiss).

Rainbow trout (Oncorhynchus mykiss) live in environments where water temperatures range between 4 °C and 20 °C. Laboratory studies demonstrate that cold and warm acclimations of male trout can have oppositional effects on cardiac hypertrophy and the collagen content of the heart. The cellular mechanisms behind temperature-induced cardiac remodelling are unclear, as is why this response differs between male and female fish. Studies with cultured trout cardiac fibroblasts suggests that collagen deposition is regulated, at least in part, by mitogen-activated protein kinase (MAPK) cell signalling pathways. We, therefore, hypothesized that temperature-dependent cardiac remodelling is regulated by these signalling pathways. To test this, male and female trout were acclimated to 18 °C (warm) in the summer and to 4 °C (cold) in the winter and the activation of MAPK pathways in the hearts were characterized and compared to that of control fish maintained at 12 °C. In addition, cardiac collagen content, cardiac morphology and the expression of gene transcripts for matrix metalloproteinases (MMP) -9, MMP-2, tissue inhibitor of matrix metalloproteinases and collagen 1α were characterized. p38 MAPK phosphorylation increased in the hearts of female fish with cold acclimation and the phosphorylation of extracellular signal-regulated kinase increased in the hearts of male fish with warm acclimation. However, there was no effect of thermal acclimation on cardiac morphology or collagen content in either male or female fish. These results indicate that thermal acclimation has transient and sex-specific effects on the phosphorylation of MAPKs but also how variable the response of the trout heart is to thermal acclimation.

How the expression of green fluorescent protein and human cardiac actin in the heart influences cardiac function and aerobic performance in zebrafish Danio rerio.

The present study examined how the expression of enhanced green fluorescent protein (eGFP) and human cardiac actin (ACTC) in zebrafish Danio rerio influences embryonic heart rate (RH ) and the swim performance and metabolic rate of adult fish. Experiments with the adults involved determining the critical swimming speed (Ucrit , the highest speed sustainable and measure of aerobic capacity) while measuring oxygen consumption. Two different transgenic D. rerio lines were examined: one expressed eGFP in the heart (tg(cmlc:egfp)), while the second expressed ACTC in the heart and eGFP throughout the body (tg(cmlc:actc,ba:egfp)). It was found that RH was significantly lower in the tg(cmlc:actc,ba:egfp) embryos 4 days post-fertilization compared to wild-type (WT) and tg(cmlc:egfp). The swim experiments demonstrated that there was no significant difference in Ucrit between the transgenic lines and the wild-type fish, but metabolic rate and cost of transport (oxygen used to travel a set distance) was nearly two-fold higher in the tg(cmlc:actc,ba:egfp) fish compared to WT at their respective Ucrit . These results suggest that the expression of ACTC in the D. rerio heart and the expression of eGFP throughout the animal, alters cardiac function in the embryo and reduces the aerobic efficiency of the animal at high levels of activity.

Data for iTRAQ-based quantification of the cardiac proteome of rainbow trout (Oncorhynchus mykiss) at rest and with exercise training.

This data article presents the first description of the rainbow trout cardiac ventricle at the level of the proteome, with more than 700 proteins identified and quantified using isobaric tags for relative and absolute quantitation (iTRAQ) and LC-MS/MS. The abundances of these proteins were compared across 4 durations of moderate exercise training (0, 4, 7, and 14 d), and a total of 107 proteins were differentially abundant during the course of the training program. The differentially abundant proteins are presented here grouped by functional classification. In the research article associated with this data [1], the temporal changes in the cardiac proteome are discussed in the context of cardiac remodelling and development of a trained heart phenotype.

Ca(2+) binding to cardiac troponin C: effects of temperature and pH on mammalian and salmonid isoforms.

A reduction in temperature lowers the Ca(2+) sensitivity of skinned cardiac myofilaments but this effect is attenuated when native cardiac troponin C (cTnC) is replaced with skeletal TnC. This suggests that conformational differences between the two isoforms mediate the influence of temperature on contractility. To investigate this phenomenon, the functional characteristics of bovine cTnC (BcTnC) and that from rainbow trout, Oncorhynchus mykiss, a cold water salmonid (ScTnC), have been compared. Rainbow trout maintain cardiac function at temperatures cardioplegic to mammals. To determine whether ScTnC is more sensitive to Ca(2+) than BcTnC, F27W mutants were used to measure changes in fluorescence with in vitro Ca(2+) titrations of site II, the activation site. When measured under identical conditions, ScTnC was more sensitive to Ca(2+) than BcTnC. At 21 degrees C, pH 7.0, as indicated by K(1/2) (-log[Ca] at half-maximal fluorescence, where [Ca] is calcium concentration), ScTnC was 2.29-fold more sensitive to Ca(2+) than BcTnC. When pH was kept constant (7.0) and temperature was lowered from 37.0 to 21.0 degrees C and then to 7.0 degrees C, the K(1/2) of BcTnC decreased by 0.13 and 0.32, respectively, whereas the K(1/2) of ScTnC decreased by 0.76 and 0.42, respectively. Increasing pH from 7.0 to 7.3 at 21.0 degrees C increased the K(1/2) of both BcTnC and ScTnC by 0.14, whereas the K(1/2) of both isoforms was increased by 1.35 when pH was raised from 7.0 to 7.6 at 7.0 degrees C.

Influences of subzero thermal acclimation on mitochondrial membrane composition of temperate zone marine bivalve mollusks.

The phospholipid and phospholipid fatty acid composition of gill mitochondrial membranes from two temperate zone marine bivalve mollusks, the quahog, Mercenaria mercenaria, and the American oyster, Crassostrea virginica, were examined after acclimation to 12 and -1 degree C. Cardiolipin (CL) was the only phospholipid with proportions altered upon acclimation to -1 degree C, increasing 188% in the mitochondrial membranes of M. mercenaria. Although the ratio of bilayer stabilizing to destabilizing lipids is frequently associated with cold acclimation in ectothermic species, no change was found in this ratio in either of the species. Polyunsaturated fatty acids (PUFA) were found only to increase in C. virginica with cold acclimation, with total n-3 PUFA increasing in the phospholipid phosphatidylethanolamine, total n-6 PUFA increasing in CL, and total PUFA increasing in phosphatidylinositol. Monounsaturated fatty acids, not PUFA, were found to have increased in M. mercenaria, with 18:1 n-9 increasing by 150% in CL, and 20:1 increasing in both CL and phosphatidylcholine, by 146 and 192%, respectively. These manipulations of membrane phospholipid and fatty acid composition may represent an attempt by these species to help maintain membrane function at low temperatures.

Mitochondrial membrane composition of two Arctic marine bivalve mollusks, Serripes groenlandicus and Mya truncata.

The phospholipid and fatty acid composition of gill mitochondria membranes from two Arctic marine bivalve mollusks, Mya truncata and Serripes groenlandicus, were examined. These animals were collected from the Arctic Ocean, where waters remain below 0 degrees C throughout the year. In both species, the primary membrane phospholipids were phosphatidylcholine, and phosphatidylethanolamine. Although a low ratio of bilayer-stabilizing phospholipids to bilayer-destabilizing phospholipids is frequently associated with cold acclimation in temperate species, this ratio is very different between the two species. The monounsaturated fatty acid 20:1 was abundant in the membranes of both Arctic species equaling 13.0% of the fatty acid composition in S. groenlandicus, and 17.7% in M. truncata. Polyunsaturated fatty acids were relatively low in the Arctic species, equaling 35.9% of total membrane fatty acids compared to that of temperate zone mollusks. It is suggested that monoenes are common in the tissues of Arctic species since they play a role in maintaining membrane function at subzero temperatures.

Compositional correlates of metabolic depression in the mitochondrial membranes of estivating snails.

The phospholipid and protein compositions of mitochondrial membranes from hepatopancreas of active and estivating terrestrial snails (Cepaea nemoralis) were compared. Mitochondria from estivating snails contained 82.7% less cardiolipin, and this was associated with an 83.9% reduction in cytochrome-c oxidase activity. Substantial changes also occurred in the proportional amounts of other individual phospholipid classes and their constituent fatty acids, including a 72% loss of total mitochondrial phospholipids, a 37% increase in monoenes, and 49% fewer n-3 fatty acids in membranes of estivating snails. These changes are consistent with those correlated with lowered metabolic rate and lower rates of proton leak in other animal models. Estivating snail hepatopancreas showed no change in total phospholipid content, indicating that the phospholipids lost from mitochondrial membranes may be sequestered elsewhere within the cell. We suggest that estivating snails remodel mitochondrial membranes as part of a coordinated, reversible suppression of mitochondrial membrane-associated processes, which may include a concomitant reduction in rates of proton pumping and leaking.

Remodeling of phospholipid fatty acids in mitochondrial membranes of estivating snails.

The effects of estivation on the phospholipid-specific fatty acid composition of mitochondrial membranes in the hepatopancreas of the terrestrial snail Cepaea nemoralis were investigated. The fatty acid composition of all phospholipids was significantly altered in snails estivating for 6 wk, indicating that substantial remodeling occurs. The most profound changes occurred in cardiolipin (CL). CL of estivating snails was 13-fold more saturated, contained 9-fold more monoenes, and had 45% fewer polyenes than in active snails. These differences were due, in part, to a reduction in linoleic acid (1 8:2n-6) content of CL from estivators. As in mammals, CL of active snails appears to preferentially incorporate 18:2n-6, which accounts for 60% of the acyl chains in this phospholipid. This proportion was reduced by 50% in estivators. Changes in the fatty acyl content of other phospholipids of estivating snails included increased monoenes in phosphatidylethanolamine (PE) and phosphatidylinositol, reduced ratios of n-3/n-6 polyenes in PE and phosphatidylcholine (PC), and an increased n-3/n-6 ratio in phosphatidylserine (PS). Arachidonic acid (20:4n-6) levels were reduced in PS but increased in CL and PC. Taken together, these alterations to fatty acid composition are consistent with decreased biological activity of membrane-related processes which occur in conjunction with the reduction of mitochondrial aerobic metabolism observed during estivation.