Infection decreases fatty acid oxidation and nuclear hormone receptors in the diaphragm

Respiratory failure is a major cause of mortality during septic shock and is due in part to decreased ventilatory muscle contraction. Ventilatory muscles have high energy demands; fatty acid (FA) oxidation is an important source of ATP. FA oxidation is regulated by nuclear hormone receptors; studies have shown that the expression of these receptors is decreased in liver, heart, and kidney during sepsis. Here, we demonstrate that lipopolysaccharide (LPS) decreases FA oxidation and the expression of lipoprotein lipase (LPL), FA transport protein 1 (FATP-1), CD36, carnitine palmitoyltransferase beta, medium chain acyl-CoA dehydrogenase (MCAD), and acyl-CoA synthetase, key proteins required for FA uptake and oxidation, in the diaphragm. LPS also decreased mRNA levels of PPARα and β/δ, RXRα, β, and γ, thyroid hormone receptor α and β, and estrogen related receptor alpha (ERRα) and their coactivators PGC-1α, PGC-1β, SRC1, SRC2, Lipin 1, and CBP. Zymosan resulted in similar changes in the diaphragm. Finally, in PPARα deficient mice, baseline CPT-1β and FATP-1 levels were markedly decreased and were not further reduced by LPS suggesting that a decrease in the PPARα signaling pathway plays an important role in inducing some of these changes. The decrease in FA oxidation in the diaphragm may be detrimental, leading to decreased diaphragm contraction and an increased risk of respiratory failure during sepsis

Deciphering the human platelet sheddome

Activated platelets shed surface proteins, potentially modifying platelet function as well as providing a source of bioactive fragments. Previous studies have identified several constituents of the platelet sheddome, but the full extent of shedding is unknown. Here we have taken a global approach, analyzing protein fragments in the supernate of activated platelets using mass spectroscopy and looking for proteins originating from platelet membranes. After removing plasma proteins and microparticles, 1048 proteins were identified, including 69 membrane proteins. Nearly all of the membrane proteins had been detected previously, but only 10 had been shown to be shed in platelets. The remaining 59 are candidates subject to confirmation. Based on spectral counts, protein representation in the sheddome varies considerably. As proof of principle, we validated one of the less frequently detected proteins, semaphorin 7A, which had not previously been identified in platelets. Surface expression, cleavage, and shedding of semaphorin 7A were demonstrated, as was its association with α-granules. Finally, cleavage of semaphorin 7A and 12 other proteins was substantially reduced by an inhibitor of ADAM17, a known sheddase. These results define a subset of membrane proteins as sheddome candidates, forming the basis for further studies examining the impact of ectodomain shedding on platelet function