External suppression causes the low expression of the Cosmc gene in IgA nephropathy.
OBJECTIVE
IgA(1) aberrant O-glycosylation is one of the main pathogeneses of IgA nephropathy (IgAN), and the core I beta3-Gal-T-specific molecular chaperone (Cosmc) mRNA expression of IgAN patients was significantly decreased. This study tried to clarify whether the down-regulation was a result of genetic disorders or external suppressions.


METHODS
Sixty-five IgAN patients, 23 non-IgAN glomerulonephritis patients and 21 normal controls were recruited. Genomic DNA was extracted and the Cosmc gene was PCR amplified and directly sequenced. Peripheral B lymphocytes of IgAN patients and normal controls were isolated, and cultured with RPMI-1640 alone or with lipopolysaccharide (LPS) for 72 h. The Cosmc mRNA expression levels at baseline, after RPMI culture or RPMI + LPS treatment were measured by real-time RT-PCR.


RESULTS
(1) The whole coding frame region of the Cosmc gene was successfully amplified and directly sequenced. Four single nucleotide polymorphisms were detected in two IgAN patients. Two were missense mutations and the others were silent mutations. However, they are different from each other, and unrelated to expression levels; (2) the baseline Cosmc mRNA expression in IgAN patients was significantly lower than normal controls (Ct(COSMC/GAPDH) 1.29 +/- 0.08 versus 1.20 +/- 0.01, 31% of normal controls); (3) the Cosmc mRNA expression level of IgAN patients was remarkably increased after the RPMI culture (1.22 +/- 0.12 versus 1.29 +/- 0.08, 219% of the baseline level), while not in normal controls and (4) treatment with LPS (culture with RPMI + LPS) could strongly inhibit the expression of Cosmc mRNA (1.25 +/- 0.01 versus 1.22 +/- 0.12, 61% of the RPMI treatment group).


CONCLUSIONS
No common Cosmc gene mutation was detected. Significantly increased Cosmc expression was observed in plasma-free culture, while LPS could significantly inhibit it, which suggested that it might not be genetic disorders but external suppression that causes the low Cosmc mRNA expression in IgAN.
Qin
Wei
W
Division of Nephrology, Sichuan University West China Hospital, 37# Guoxue Xiang, Wu Hou District, Chengdu, Sichuan Province 610041, People's Republic of China.
Zhong
Xiang
X
Fan
Jun Ming
JM
Zhang
Ying Juan
YJ
Liu
Xian Rong
XR
Ma
Xing Yi
XY
D000328:Adult; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D001483:Base Sequence; D016022:Case-Control Studies; D017931:DNA Primers / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects; D005260:Female; D005922:Glomerulonephritis, IGA / Q000235:genetics* / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D007070:Immunoglobulin A / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D018832:Molecular Chaperones / Q000235:genetics*; D020125:Mutation, Missense; D020641:Polymorphism, Single Nucleotide; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
C505369:C1GALT1C1 protein, human; D017931:DNA Primers; D007070:Immunoglobulin A; D008070:Lipopolysaccharides; D018832:Molecular Chaperones; D012333:RNA, Messenger