Cutaneous water loss and sphingolipids in the stratum corneum of house sparrows,Passer domesticusL., from desert and mesic environments as determined by reversed phase high-performance liquid chromatography coupled with atmospheric pressure photospray ionization mass spectrometry

Abstract

SUMMARYBecause cutaneous water loss (CWL) represents half of total water loss in birds, selection to reduce CWL may be strong in desert birds. We previously found that CWL of house sparrows from a desert population was about 25% lower than that of individuals from a mesic environment. The stratum corneum (SC), the outer layer of the epidermis, serves as the primary barrier to water vapor diffusion through the skin. The avian SC is formed by layers of corneocytes embedded in a lipid matrix consisting of cholesterol, free fatty acids and two classes of sphingolipids, ceramides and cerebrosides. The SC of birds also serves a thermoregulatory function; high rates of CWL keep body temperatures under lethal limits in episodes of heat stress.In this study, we used high-performance liquid chromatography coupled with atmospheric pressure photoionization-mass spectrometry (HPLC/APPI-MS) to identify and quantify over 200 sphingolipids in the SC of house sparrows from desert and mesic populations. Principal components analysis (PCA) led to the hypotheses that sphingolipids in the SC of desert sparrows have longer carbon chains in the fatty acid moiety and are more polar than those found in mesic sparrows. We also tested the association between principal components and CWL in both populations. Our study suggested that a reduction in CWL found in desert sparrows was, in part, the result of modifications in chain length and polarity of the sphingolipids, changes that apparently determine the interactions of the lipid molecules within the SC.

Developmental plasticity of cutaneous water loss and lipid composition in stratum corneum of desert and mesic nestling house sparrows

“…The SC is formed by flattened dead cells, called corneocytes, embedded in an extracellular lipid matrix consisting of cholesterol, free fatty acids (FFA), ceramides (a sphingosine molecule ester bonded to a fatty acid) and cerebrosides (a ceramide molecule attached to a hexose). Studies on the SC of larks, house sparrows, and several species of tropical birds suggest that changes in the proportions of FFA and ceramides in the extracellular matrix of the SC influence rates of CWL (11,13,14). Desert birds have a lower percentage of FFA and a higher percentage of ceramides in the SC than birds from mesic environments, a relationship observed across and within species (11,13).…”

“…Variation in CWL is thought to be primarily mediated by alteration in lipid composition of SC (11)(12)(13)(14). The SC is formed by flattened dead cells, called corneocytes, embedded in an extracellular lipid matrix consisting of cholesterol, free fatty acids (FFA), ceramides (a sphingosine molecule ester bonded to a fatty acid) and cerebrosides (a ceramide molecule attached to a hexose).…”

“…Desert birds have a lower percentage of FFA and a higher percentage of ceramides in the SC than birds from mesic environments, a relationship observed across and within species (11,13). Changes in the ratios of lipid classes in the SC might influence CWL in birds (14). Apparently, appropriate ratios of ceramides, cerebrosides, and FFAs are necessary for the formation of intracellular lipid bilayers, called lamellae, and the molecular organization of these lamellae affects CWL (14,15).…”

“…Changes in the ratios of lipid classes in the SC might influence CWL in birds (14). Apparently, appropriate ratios of ceramides, cerebrosides, and FFAs are necessary for the formation of intracellular lipid bilayers, called lamellae, and the molecular organization of these lamellae affects CWL (14,15).…”

“…We chose to study the effect of humidity on the SC, given that the properties of the permeability barrier, at least in mammals, change in response to the level of hydration of the SC (14,15,26). Our study showed that, regardless of environmental origin, nestling house sparrows had a more permeable skin than that of adults exposed to their natural environment.…”