News Feature: Deadly deficiency at the heart of an environmental mystery

Low thiamine concentrations are associated with altered cardiac morphology across reproductive life histories of spawning Chinook Salmon

OBJECTIVE

Thiamine deficiency is a widespread issue in salmonine species and has been reported to induce changes in cardiac morphology and cardiac dysfunction in Lake Trout Salvelinus namaycush. Here, we assess the effects of thiamine concentration on the ventricular morphology of three reproductive life histories (jack males, hooknose males, and females) of wild spawning Chinook Salmon Oncorhynchus tshawytscha.

METHODS

Fish were sampled from the Credit River (a Lake Ontario tributary), and skeletal muscle, ventricle, and liver thiamine concentrations were quantified using high-performance liquid chromatography. A subset of ventricles was retained for histological analyses. Hematoxylin and eosin-stained slides were used to measure cardiomyocyte width and compact myocardium thickness, and Masson's trichrome-stained slides were used to measure levels of cardiac fibrosis. Level of spawning senescence was quantified based on a qualitative score.

RESULTS

Thiamine levels did not differ significantly among life histories, except that hooknose males had significantly greater skeletal muscle thiamine concentrations than females. Thiamine concentrations in skeletal muscle and the ventricle were positively correlated. Across all life histories, lower concentrations of thiamine in skeletal muscle were associated with increased levels of cardiomyocyte hypertrophy and cardiac fibrosis, independent of their relationships with ventricle mass and level of spawning senescence. No significant relationships were observed with compact myocardium thickness.

CONCLUSIONS

Low thiamine concentrations are associated with pathological alterations in cardiac morphology across reproductive life histories in spawning Chinook Salmon.

Thiamine deficiency: a commonly unrecognised but easily treatable condition

Thiamine is present in many foods and is well recognised as an essential nutrient critical for energy metabolism. While thiamine deficiency is commonly recognised in alcoholism, it can present in many other settings where it is often not considered and goes unrecognised. One challenging aspect to diagnosis is that it may have varied metabolic, neurological and cardiac presentations. Here we present an overview of the disorder, focusing on the multiple causes and clinical presentations. Interestingly, thiamine deficiency is likely increasing in frequency, especially among wildlife, where it is linked with changing environments and climate change. Thiamine deficiency should be considered whenever neurological or cardiological disease of unknown aetiology presents, especially in any patient presenting with lactic acidosis.

Form and Function of the Vertebrate and Invertebrate Blood-Brain Barriers

The need to protect neural tissue from toxins or other substances is as old as neural tissue itself. Early recognition of this need has led to more than a century of investigation of the blood-brain barrier (BBB). Many aspects of this important neuroprotective barrier have now been well established, including its cellular architecture and barrier and transport functions. Unsurprisingly, most research has had a human orientation, using mammalian and other animal models to develop translational research findings. However, cell layers forming a barrier between vascular spaces and neural tissues are found broadly throughout the invertebrates as well as in all vertebrates. Unfortunately, previous scenarios for the evolution of the BBB typically adopt a classic, now discredited 'scala naturae' approach, which inaccurately describes a putative evolutionary progression of the mammalian BBB from simple invertebrates to mammals. In fact, BBB-like structures have evolved independently numerous times, complicating simplistic views of the evolution of the BBB as a linear process. Here, we review BBBs in their various forms in both invertebrates and vertebrates, with an emphasis on the function, evolution, and conditional relevance of popular animal models such as the fruit fly and the zebrafish to mammalian BBB research.

Linking gene expression patterns with survival studies elucidates adaptive potential in changing environments

A major goal in ecology, evolution and conservation biology is understanding how species adapt to changing conditions and using that information to improve conservation actions. Primary to advancing our understanding of adaptation and adaptive potential is determining the causes and consequences of the genetic and phenotypic intraspecific variation that allows for adaptation. However, few studies have been able to link the variation present in molecular process under differing conditions to intraspecific variation in survival. In a From the Cover article in this issue of Molecular Ecology, Harder et al explore the relationship between molecular process and survival to understand the adaptive variation underlying tolerance to low thiamine (vitamin B1, an essential micronutrient) conditions in Atlantic salmon (Salmo salar). Thiamine is required for metabolic functioning, including energy production and nervous and cardiovascular system functioning. By combining controlled breeding and phenotyping with a survival study and transcriptomics, the authors are able to quantify among-family differences in survival under low thiamine conditions. They find wide variation in survival among families, and this survival is linked to differences in gene expression patterns. Their study elucidates the importance of combining different data types to characterize within-population phenotypic variation and understand how that variation may lead to genetic adaptation under stressful conditions.