Serum bikunin is a biomarker of linkeropathies

Serum bikunin isoforms in congenital disorders of glycosylation and linkeropathies

“…The UTI protein band was similar to that of the control in 2/3 ATP6V0A2‐CDG cases and shared a mildly higher molecular weight (MW) in other proton pump‐related CDG cases (Figure 2A). However, the corresponding MW values remain included within normal values we determined previously 2 . Concerning the heavy forms, the overall signal levels of ITI and PαI were dramatically decreased compared to control with exception of one ATP6AP1‐CDG sample showing a discrete reduced signal.…”

“…Western-blot patterns of all Bkn isoforms from one representative control, various type 2 CDG (CDG-II), and linkeropathy samples are shown in Figure 2A (free Bkn and UTI) and Figure 2B (PαI and ITI). As previously described, 2 the Bkn patterns from the 10-fold diluted control serum (Figure 2A) presented a small band at 25 kDa consistent with free Bkn and a 35 kDa marked and large band corresponding to UTI, that is, Bkn linked to the variable-sized CS chain (Bkn-CS). Using a 250-fold diluted serum, the heavy Bkn isoforms could be seen ( Figure 2B) as two bands at 125 and 225 kDa corresponding, respectively, to PαI (Bkn-CS-HC) and ITI (Bkn-CS-2HC).…”

“…For the Western‐blot analysis, sera/plasma were either diluted 1/10 (for UTI and free Bkn) or 1/250 (for ITI and PαI) in water. These dilutions were considered as “optimal” based on our previous work 2 and on the prior analysis of various sera and corresponding plasma sequentially diluted within 1/10 to 1/4000 (Supp. Figure S1).…”

“…Three major serum isoforms have been extensively described: the inter-α-trypsin inhibitor (ITI) and the pro-α-trypsin inhibitor (PαI), carrying respectively two and one HC, as well as the urinary trypsin inhibitor (UTI), which corresponds to Bkn linked to the CS chain. 1 In addition, we showed that free Bkn (ie, the core protein) could be detected at low level in serum 2 ( Figure 1A).…”

“…15 In linkeropathies, that is, rare skeletal/osteoarticular genetic diseases affecting the biosynthesis of the common initial tetrasaccharide (-GlcA-Gal-Gal-Xyl-O-Ser-) of protein-linked glycosaminoglycans (GAG), we previously showed high levels of abnormal serum Bkn light forms suggesting a potential interest for screening purposes. 2 In this work, we performed Western-blot analysis of all serum Bkn isoforms from patients with various congenital disorders of glycosylation (CDG) including defects in the V-ATPase Golgi protons pump (ATP6V0A2-CDG, CCDC115-CDG, and ATP6AP1-CDG), in manganese (Mn 2+ ) homeostasis (TMEM165-CDG), in tethering factors (conserved oligomeric Golgi complex [COG]-CDG) and in activated sugar transporters (SLC35A2-CDG and SLC35A3-CDG). We focused on these CDG because we anticipated the presence of abnormal Bkn isoforms, linked to impaired Golgi homeostasis (V-ATPase deficiencies, TMEM165-CDG, COG-CDG), and/or associated with GAG biosynthesis defects leading to skeletal clinical phenotypes (TMEM165-CDG, SLC35A2-CDG, and SLC35A3-CDG).…”