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In this work, we present a novel modeling framework for understanding the dynamics of homeostatic regulation. Inspired by engineering control theory, this framework incorporates unique features of biological systems. First, biological variables often play physiological roles, and taking this functional context into consideration is essential to fully understand the goals and constraints of homeostatic regulation. Second, biological signals are not abstract variables, but rather material molecules that may undergo complex turnover processes of synthesis and degradation. We suggest that the particular nature of biological signals may condition the type of information they can convey, and their potential role in shaping the dynamics and the ultimate purpose of homeostatic systems. We show that the dynamic interplay between regulated variables and control signals is a key determinant of biological homeostasis, challenging the necessity and the convenience of strictly extrapolating concepts from engineering control theory in modeling the dynamics of homeostatic systems. This work provides a simple, unified framework for studying biological regulation and identifies general principles that transcend molecular details of particular homeostatic mechanisms. We show how this approach can be naturally applied to apparently different regulatory systems, contributing to a deeper understanding of homeostasis as a fundamental process in living systems. [ABSTRACT FROM AUTHOR]

Gelatin-based traditional Chinese medicines have long been used to treat anemia. Here, rats on the gelatin-based AIN-93G diet showed higher hemoglobin regeneration efficiencies and liver iron concentrations than those fed the diets based on several other animal proteins from muscle sarcoplasm and fibrils, egg white, whey and casein. However, among these animal proteins, gelatin had the lowest digestibility under simulated gastric-proximal intestinal digestion, and its hydrolysate showed the lowest capacity to aid iron absorption in Caco-2 monolayers via templating ferric oxyhydroxide nanoparticles. In another rat hemoglobin regeneration assay, dietary supplementations with gelatin and its two major degradation products, glycine and prolyl-hydroxyproline, revealed that gelatin boosted iron absorption not through glycine, but rather via prolyl-hydroxyproline, which had inhibitory and stimulatory effects on the plasma levels of hepcidin and erythropoietin, respectively. Dietary gelatin thus seems to enhance non-heme iron absorption via regulating systemic iron homeostasis rather than via solubilizing luminal ferric iron.

• Dietary gelatin boosted iron absorption in rat hemoglobin regeneration assays. • Gelatin had a weak capacity to solubilize luminal ferric iron during digestion. • Prolyl-hydroxyproline is the functional degradation product of dietary gelatin. • Prolyl-hydroxyproline decreased hepcidin and increased erythropoietin in plasma. Gelatin-based traditional Chinese medicines have long been used to treat anemia. Here, rats on the gelatin-based AIN-93G diet showed higher hemoglobin regeneration efficiencies and liver iron concentrations than those fed the diets based on several other animal proteins from muscle sarcoplasm and fibrils, egg white, whey and casein. However, among these animal proteins, gelatin had the lowest digestibility under simulated gastric-proximal intestinal digestion, and its hydrolysate showed the lowest capacity to aid iron absorption in Caco-2 monolayers via templating ferric oxyhydroxide nanoparticles. In another rat hemoglobin regeneration assay, dietary supplementations with gelatin and its two major degradation products, glycine and prolyl-hydroxyproline, revealed that gelatin boosted iron absorption not through glycine, but rather via prolyl-hydroxyproline, which had inhibitory and stimulatory effects on the plasma levels of hepcidin and erythropoietin, respectively. Dietary gelatin thus seems to enhance non-heme iron absorption via regulating systemic iron homeostasis rather than via solubilizing luminal ferric iron. [ABSTRACT FROM AUTHOR]