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beta(2)-Microglobulin modified with advanced glycation end products delays monocyte apoptosis
1Duke Institute of Renal Outcomes Research and Health Policy, Division of Nephrology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Background:
A local inflammatory reaction to beta(2)-microglobulin (beta(2)m) amyloid deposits by monocytes/macrophages is a characteristic histologic feature of dialysis-related amyloidosis (DRA). Since beta(2)m modified with advanced glycation end products (AGE-beta(2)m) is a major constituent of amyloid in DRA, we tested the hypothesis that AGE-beta(2)m affects apoptosis and phenotype of human monocytes.
Methods:
Human peripheral blood monocytes were incubated with or without in vitro-derived AGE-beta(2)m, and their viability, extent of apoptosis, morphology, and function examined over the subsequent four days.
Results:
AGE-modified but not unmodified beta(2)m significantly delayed spontaneous apoptosis of human peripheral blood monocytes in adherent and nonadherent cultures. The effect of AGE-beta(2)m on monocytes apoptosis was time- and dose-dependent and was attenuated by a blocking antibody directed against the human AGE receptor (RAGE). There was no difference in effect between AGE-beta(2)m and that of AGE-modified human serum albumin. Culture of monocytes with AGE-beta(2)m did not alter membrane expression of Fas or Fas ligand. Monocytes cultured with AGE-beta(2)m underwent substantial changes in morphology similar to those observed when monocytes differentiate into macrophages. The cultured cells increased in size and vacuolization, and their content of beta-glucuronidase and acid phosphatase increased by 5- to 10-fold at day 4. Expression of the monocyte--macrophage membrane antigens HLA-DR, CD11b, and CD11c also increased at day 4. Although exhibiting phenotypic characteristics of macrophages, monocytes cultured with AGE-beta(2)m functioned differently than macrophages cultured with serum. Superoxide production in response to phorbol myristic acetate was maintained in monocytes cultured with AGE-beta(2)m, but declined with time in cells cultured with serum. Constitutive synthesis of tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta) and prostaglandin E2 (PGE2) increased in monocytes cultured for four to six days with AGE-beta(2)m.
Conclusions:
These findings support a novel role for AGE-modified proteins such as AGE-beta(2)m that may contribute to the development of a local inflammatory response, with predominant accumulation of monocytes/macrophages, in DRA.
Insights
Advanced glycation end product-modified beta(2)-microglobulin (AGE-beta(2)m) delays monocyte apoptosis and promotes macrophage-like differentiation. These findings suggest AGE-beta(2)m contributes to inflammation in dialysis-related amyloidosis (DRA).
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Dialysis-related amyloidosis (DRA) is characterized by local inflammation from beta(2)-microglobulin (beta(2)m) amyloid deposits.
- Advanced glycation end product-modified beta(2)m (AGE-beta(2)m) is a key component of DRA amyloid.
- The study investigates the impact of AGE-beta(2)m on human monocyte apoptosis and phenotype.
Purpose of the Study:
- To determine if AGE-beta(2)m influences monocyte apoptosis.
- To examine the phenotypic and functional changes in monocytes exposed to AGE-beta(2)m.
- To explore the role of AGE-beta(2)m in the inflammatory processes of DRA.
Main Methods:
- Human peripheral blood monocytes were cultured with or without in vitro-derived AGE-beta(2)m for four days.
- Monocyte viability, apoptosis, morphology, and function were assessed.
- Changes in cell surface markers, enzyme activity, and cytokine production were analyzed.
Main Results:
- AGE-beta(2)m significantly delayed spontaneous monocyte apoptosis in a time- and dose-dependent manner, inhibited by RAGE antibody.
- Monocytes exposed to AGE-beta(2)m exhibited morphological changes consistent with macrophage differentiation, including increased size and vacuolization.
- Upregulation of monocyte-macrophage antigens (HLA-DR, CD11b, CD11c) and increased production of TNF-alpha, IL-1 beta, and PGE2 were observed.
Conclusions:
- AGE-modified proteins, such as AGE-beta(2)m, play a significant role in initiating local inflammatory responses.
- The accumulation of monocytes/macrophages in DRA may be driven by the effects of AGE-beta(2)m on these cells.
- These findings provide insights into the pathogenesis of dialysis-related amyloidosis.