Deciphering N‑Glycosylation Dynamics of Serum Monoclonal Immunoglobulins in Multiple Myeloma via EThcD-sceHCD-MS/MS

Serum glycoprotein glycosylation
changes can indicate disease onset
and progression. However, the site-specific N-glycosylation of monoclonal
immunoglobulins (M-proteins) in multiple myeloma (MM) and its clinical
implications are unclear. In this study, we isolated pathogenic micromonoclonal
IgA or IgG (approximately 2 μg) from IgA-MM patients (n = 22) and IgG-MM patients (n = 30), and
normal polyclonal IgA and IgG from healthy controls (HCs) (n = 16). Using EThcD-sceHCD-MS/MS, the N-glycosylation dynamics
of serum M-proteins in MM were determined. Compared with polyclonal
IgA1 from HCs, monoclonal IgA1 from IgA-MM patients had higher fucosylation
(58.1% vs 32.1%, p < 0.001), sialylation (68.0%
vs 50.8%, p = 0.011), and mannosylation (1.5% vs
0.3%, p < 0.001). While, monoclonal IgG1 from
IgG-MM patients had higher fucosylation (97.8% vs 95.3%, p < 0.001). In addition, specific N-glycan abundances correlated
with MM clinical features: for IgA1, HexNAc5Hex5Fuc1NeuAc1 was associated
with hypocomplementemia; for IgG1, HexNAc4Hex3Fuc1 was associated
with the serum albumin level (r = −0.363, p = 0.049) and estimated glomerular filtration rate (r = −0.433, p = 0.017); and HexNAc4Hex5
was associated with therapeutic prognosis. In conclusion, monoclonal
IgA1 and IgG1 in MM patients and their polyclonal isotypes in HCs
have distinct N-glycosylation profiles, and specific N-glycans of
M-proteins are associated with MM characteristics and therapeutic
prognosis.