Rapid and parallel changes in activity and mRNA of intestinal peptidase to match altered dietary protein level in juvenile house sparrows (Passer domesticus)

Although dietary flexibility in digestive enzyme activity (i.e., reaction rate) is widespread in vertebrates, mechanisms are poorly understood. When laboratory rats are switched to higher protein diet, the activities of apical intestinal peptidases increase within 15 h, in some cases by rapid increase in enzyme transcription followed by rapid translation and translocation to the intestine's apical, brush border membrane (BBM). Focusing on aminopeptidase-N (APN), we studied intestinal digestive enzyme flexibility in birds, relying on activity and mRNA data from the same animals. Our model was nestling house sparrows (Passer domesticus), already known to modulate intestinal peptidase activity when switching between lower and higher protein diets. Twenty-four hours after a switch from an adequate, lower protein diet to a higher protein diet, APN activity was increased in both whole intestinal tissue homogenates and in isolated BBM, but not at 12 h post-diet switch. Twenty-four hours after a reverse switch back to the lower protein diet, APN activity was decreased, but not at 12 h post-diet switch. Changes in APN activity in both diet switch experiments were associated with parallel changes in APN mRNA. Although transcriptional changes seem an important mechanism underlying dietary modulation of intestinal peptidase in both nestling house sparrows and laboratory rodents, the time course for modulation in nestlings seemed slower (to take approximately twice as long) compared to laboratory rodents. It may be ecologically advantageous if nestlings biochemically restructure their gut in response to a sustained increase in insects and protein intake rather than one or a few lucky insect meals.

Dietary adaptation to high starch involves increased relative abundance of sucrase-isomaltase and its mRNA in nestling house sparrows

Dietary flexibility in digestive enzyme activity is widespread in vertebrates, but mechanisms are poorly understood. When laboratory rats are switched to higher carbohydrate diet, activity of intestinal sucrase-isomaltase (SI) increases within 6-12 h, mainly by rapid increase in enzyme transcription followed by rapid translation and translocation to the intestine's apical, brush border membrane (BBM). We performed the first unified study of the overall process in birds, relying on activity, proteomic and transcriptomic data from nestling house sparrows (Passer domesticus). They switch naturally from low-starch insect diet to higher-starch seed diet, and SI is responsible for all their intestinal maltase and sucrase activities. Twenty-four hours after a switch to a high-starch diet, SI activity was increased, but not at 12 h post-diet switch. SI was the only hydrolase increased in the BBM, and its relative abundance and activity were positively correlated. Twenty-four hours after a reverse switch back to the lower-starch diet, SI activity was decreased, but not at 12 h post-diet switch. Parallel changes in SI mRNA were associated with the changes in SI activity in both diet switch experiments. This is the first demonstration that birds may rely on rapid increase in abundance of SI and its mRNA when adjusting to high starch diet. Although the mechanisms underlying dietary induction of intestinal enzymes seem similar in nestling house sparrows and laboratory rodents, time course for modulation in nestlings seemed half as fast compared to laboratory rodents. This may be understandable considering differences in ecology and evolution.

Fatty acid metabolism and modifications in Chironomus riparius

A priori knowledge of fatty acid modifications in consumers is essential for studies using fatty acids as biomarkers. We investigated fatty acid metabolism and possible modification pathways in benthic invertebrate Chironomus riparius larvae (Diptera). We conducted diet manipulation experiments using natural food sources (two chlorophyte algae, a diatom and a non-toxic cyanobacterium). We also did a diet-switch experiment on two different resources, fish food flakes TetraMin ® and cyanobacterium Spirulina , to study fatty acid turnover in Chironomus . Results of the diet manipulation experiments indicate that Chironomus larvae have a strong tendency to biosynthesize 20:5n-3 and 20:4n-6 from precursor fatty acids, and that the dietary availability of polyunsaturated fatty acids (PUFA) does not control larval growth. Fatty acid modifications explain why low dietary availability of PUFA did not significantly limit growth. This has ecologically relevant implications on the role of benthic chironomids in conveying energy to upper trophic level consumers. A diet-switch experiment showed that the turnover rate of fatty acids in Chironomus is relatively fast––a few days. The compositional differences of algal diets were large enough to separate Chironomus larvae into distinct groups even if significant modification of PUFA was observed. In summary, fatty acids are excellent dietary biomarkers for Chironomus , if modifications of PUFA are considered, and will provide high-resolution data on resource use. This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

The isotopic nitrogen turnover rate as a proxy to evaluate in the long-term the protein turnover in growing ruminants

Protein turnover is an energy-consuming process that is essential for ensuring the maintenance of living organisms. Gold standard methods for whole-body protein turnover (WBPT) measurement have inherent drawbacks precluding their generalization for large farm animals and use during long periods. Here, we proposed a non-invasive proxy for the WBPT over a long period of time and in a large number of beef cattle. The proxy is based on the rate at which urine-N and plasma proteins are progressively depleted in terms of 15N after a slight decrease in the isotopic N composition of the diet (i.e. diet switch). We aimed to test the ability of this proxy to adequately discriminate the WBPT of 36 growing-fattening young bulls assigned to different dietary treatments known to impact the WBPT rate, with different protein contents (normal v. high) and amino acid profiles (balanced v. unbalanced in methionine). The 15N depletion rate found in plasma proteins represented their fractional synthesis rate, whereas the slow depletion rate found in urine was interpreted as a proxy of the WBPT. The proxy tested in urine suggested different WBPT values between the normal- and high-protein diets but not between the balanced and unbalanced methionine diets. In contrast, the proxy tested in plasma indicated that both dietary conditions affected the fractional synthesis rate of plasma proteins. We considered that the rate at which urine is progressively 15N-depleted following an isotopic diet switch could be proposed as a non-invasive proxy of the WBPT rate in large farm animals.

A switch from high-fat to normal diet does not restore sperm quality but prevents metabolic syndrome

In recent decades, the prevalence of metabolic diseases has concomitantly increased with a decline on fertility rates and sperm quality. High-fat diets (HFD) are seldom considered part of the problem, but the molecular mechanisms underlying its effects on male fertility remain poorly understood. Herein we postulated that HFD alter sperm quality. We evaluated the effects of switching from a HFD to a normal diet in early adulthood on metabolic disease onset, testicular metabolism and sperm quality. Thirty-six male C57BL6/J mice were divided in: a control group fed with standard chow; a group fed with HFD for 200 days; and a group fed with HFD for 60 days and then with standard chow (HFDt). Biometric data and whole-body metabolism were assessed. Epididymal sperm was studied for concentration, motility, viability and morphology. 1H-NMR metabolomics approach was performed on testicular extracts to trace the metabolic changes. Diet switch reduced body weight and fat mass, preventing metabolic syndrome onset. However, sperm viability, motility and morphology were deteriorated by HFD consumption and not restored by diet switch. HFD induced irreversible changes in pyruvate and glutamate metabolism, ethanol degradation and ammonia recycling in testis. Furthermore, HFDt changed purine and cysteine metabolism, urea cycle, and glutathione content. Overall, HFD caused irreversible changes in testicular metabolism even after switching to normal diet. HFD feeding until early adulthood decreases sperm quality, which cannot be restored by diet switch or weight loss, even when development of metabolic syndrome is avoided.