Sensitive asprosin detection in clinical samples reveals serum/saliva correlation and indicates cartilage as source for serum asprosin

Abstract

The C-terminal pro-fibrillin-1 propeptide asprosin is described as white adipose tissue derived hormone that stimulates rapid hepatic glucose release and activates hunger-promoting hypothalamic neurons. Numerous studies proposed correlations of asprosin levels with clinical parameters. However, the enormous variability of reported serum and plasma asprosin levels illustrates the need for sensitive and reliable detection methods in clinical samples. Here we report on newly developed biochemical methods for asprosin concentration and detection in several body fluids including serum, plasma, saliva, breast milk, and urine. Since we found that glycosylation impacts human asprosin detection we analyzed its glycosylation profile. Employing a new sandwich ELISA revealed that serum and saliva asprosin correlate strongly, depend on biological sex, and feeding status. To investigate the contribution of connective tissue-derived asprosin to serum levels we screened two cohorts with described cartilage turnover. Serum asprosin correlated with COMP, a marker for cartilage degradation upon running exercise and after total hip replacement surgery. This together with our finding that asprosin is produced by primary human chondrocytes and expressed in human cartilage suggests a contribution of cartilage to serum asprosin. Furthermore, we determined asprosin levels in breast milk, and urine, for the first time, and propose saliva asprosin as an accessible clinical marker for future studies.

Transglutaminase mediated asprosin oligomerization allows its tissue storage as fibers

“…When recombinant asprosin was subjected to size exclusion chromatography (SEC), the obtained chromatogram showed two main asprosin containing peaks eluting at fraction numbers corresponding to higher molecular weight species (Fig. 3A) than the previously determined 37 kDa of glycosylated recombinant asprosin (14). In line with this finding, analysis of asprosin fractions directly after affinity purification by native-PAGE revealed the accumulation of asprosin in the stacking gel with no detected migration into the gel (Fig.…”

“…In the current view, asprosin is mainly produced by WAT from where it is released into the blood in monomeric form. However, our previous findings showed that asprosin is synthesized and secreted by connective tissue resident cells such as fibroblasts and chondrocytes (14) -a finding which supports the notion of local asprosin storage within tissue-specific microenvironments. Here, by employing newly generated specific asprosin antibodies we monitored the distribution pattern of asprosin in various human and murine connective tissues, including placenta, and muscle.…”

Correlation of metabolic characteristics with maternal, fetal and placental asprosin in human pregnancy

“…The asprosin sandwich ELISA was produced in our laboratory, intensively tested and validated by surface plasmone resonance and interaction studies ( 16 ). The detection sensitivity ranged at <65 pg/mL.…”

“…However, it has been recently shown that asprosin is expressed in human placenta and elevated in the plasma of pregnant women complicated with GDM and their fetal umbilical blood ( 14 ). Since there is an urgent need for a reliable and sensitive method to determine plasma asprosin levels ( 15 ), our laboratory took the initiative to develop a functional and dependable asprosin ELISA ( 16 ).…”

Asprosin in health and disease, a new glucose sensor with central and peripheral metabolic effects

“…Recent studies reported measurable amounts of asprosin in different body fluids such as saliva, breast milk, urine, serum, and plasma ( 18 – 20 ). Interestingly, asprosin was found to be expressed in the ovaries, placenta and human cartilage ( 19 , 21 , 22 ). A strong correlation was reported between serum asprosin levels and a specific marker for cartilage degradation termed cartilage oligomeric matrix protein (COMP) in patients subjected to total hip replacement surgery ( 19 ).…”