Transcriptomic and proteomic analysis of the underlying mechanisms of digestion of triacylglycerols and phosphatides and absorption and fate of fatty acids along the midgut of Musca domestica

Dietary Lipids and Their Metabolism in the Midgut

Animals use dietary lipids to sustain their growth and survival. Insects can synthesize fatty acids (FAs) and are autotroph for a number of lipids, but auxotroph for specific lipids classes (e.g. sterols, polyunsaturated FAs). Once ingested, lipids are hydrolysed in the intestinal lumen and taken up into intestinal cells within specific regions of the insect digestive tract. These lipids can be either stored in the intestinal cells or exported through the haemolymph circulation to specific organs. In this chapter, we describe the various lipids provided by insect diets, their extracellular hydrolysis in the gut lumen and their intake and metabolic fate in the intestinal cells. This chapter emphasizes the critical role of the digestive tract and its regionalization in processing dietary lipids prior to their transfer to the requiring tissues.

Protein digestion and amino acid absorption mechanisms along the midgut of Musca domestica larvae

A model of protein digestion and peptide and amino acid absorption along the midgut of Musca domestica larvae was proposed and supported by RNA-Seq analyses, protein bioinformatics, microvillar-membrane-enriched midgut proteomics, and enzymatic activities. Peptidase genes are highly expressed in the posterior midgut (PM), whereas those for cathepsins have expression limited to the middle midgut (MM). MM has the lowest levels of gene expression of almost all peptidases but has high expression of genes for membrane-bound serine endopeptidases. The anterior midgut (AM) has intermediate expression values of serine endopeptidase and aminopeptidase (AP) genes and low expression of carboxypeptidases (CPs). Gene expression and peptidase activities were usually consistent for putative intracellular and membrane-bound enzymes. However, secreted peptidase gene expression and activities have divergent values, especially in the PM, which may be due to the countercurrent water flux causing enzyme recycling, thus decreasing their excretion. Data suggest that Trys and APs act in the AM. In the acidic MM, lysozymes kill microorganisms found in the diet, releasing proteins digested by cathepsins D, which may also digest Trys coming from the AM. Finally, highly active serine endopeptidases, CPs, dipeptidases, and APs complete protein digestion in PM. Absorption of peptides and amino acids coupled to protons may occur along the midgut, especially in PM, as occurs for facilitated amino acid transport. Absorption with sodium ions is probably restricted to AM and PM. Our findings provide valuable insights into the protein digestion and amino acid absorption mechanism in M. domestica larvae.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.