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[Phenotypic and functional alterations of mesangial cells in patients with diabetic nephropathy]
1Research Institute of Nephrology, Jinling Hospital, Nanjing University School of Medicine, Nanjing 210002, China.
Objective:
To explore the phenotypic and functional changes of glomerular mesangial cells (MC) in the development of diabetic nephropathy (DN).
Methods:
Renal biopsy specimens were obtained from patients with type II DN. MC from microdissected glomeruli were cultured in vitro. Both the cells deriving from minute piece of renal biopsy specimen of type 2 DN with overt proteinuria and from transplanted donors' kidneys were investigated. Cell volume, RNA/DNA ratio and the production of fibronectin and glucose transporter 1 (GLUT1) was analyzed by flow ctrometry. Cell proliferation was determined by 3H-Tdr incorporation assay and doubling time. Immunofluorescence staining and flow ctrometry were used to examine the expression of alpha-smooth muscle actin and extracellular matrix. The mRNA expression of GLUT1 was determined by Northern blotting and flow cytometry. Glucose uptake rate by MC was detected using the [3H]-2-DG. The activity of glutamine: fructose-6-P aminotransferase (GFAT), the key enzyme of hexosamine pathway, was measured by spetrophotometry method. Specimens from transplanted kidneys were used a s controls.
Results:
In specimens from patients with type II DN, increase in volume of MC (in arbitrary units) and RNA/DNA ratio (0.29 +/- 0.05 vs. 0.17 +/- 0.03, P < 0.01) accompanied with high 3H-Tdr incorporation rate (1,898 +/- 421 vs. 1,221 +/- 262, P < 0.05) and shorter doubling time (31.6 +/- 1.84 h vs. 35.0 +/- 5.37 h, P < 0.05) was found in comparison with the control. The synthesis of alpha-smooth muscle actin and extracellular matrix, including fibronectin and laminin, increased. Enhanced mRNA and protein expression of GLUT1 were verified in MC from DN. 2-DG uptake assay showed increased glucose uptake rate in MC from DN compared to the control(1,592 cpm x 10(5) cell-1 vs. 1,275 cpm x 10(5) cell-1, P < 0.05). Furthermore, MC from DN demonstrated a higher GFAT activity as compared to control.
Conclusion:
Dramatic phenotypic and functional changes, including cell hypertrophy, increased cell turnover, excessive formation of ECM, enhanced expression of GLUT1 as well as alterration in cell glucose uptake, excessive flux of glucose metabolism through the hexosamine pathway, occur in MC from type II DN. The above mentioned phenotypic and functional changes may be the basis of pathogenesis of MC in DN.
Insights
Glomerular mesangial cells (MC) in diabetic nephropathy (DN) show hypertrophy, increased turnover, and excessive extracellular matrix production. These cells also exhibit altered glucose metabolism, including enhanced glucose transporter 1 (GLUT1) expression and increased hexosamine pathway flux, contributing to DN pathogenesis.
Area of Science:
- Nephrology
- Cell Biology
- Metabolic Disorders
Context:
- Diabetic nephropathy (DN) is a major complication of diabetes mellitus.
- Glomerular mesangial cells (MC) play a critical role in the structural and functional integrity of the glomerulus.
- Understanding MC changes in DN is crucial for developing targeted therapies.
Purpose:
- To investigate the phenotypic and functional alterations of MC in type II diabetic nephropathy.
- To analyze changes in cell size, proliferation, extracellular matrix production, and glucose metabolism in MC from DN patients.
Summary:
- MC from type II DN patients exhibited significant hypertrophy (increased cell volume) and accelerated proliferation (higher 3H-Tdr incorporation, shorter doubling time) compared to controls.
- DN-MC showed increased synthesis of alpha-smooth muscle actin and extracellular matrix components like fibronectin and laminin.
- Enhanced expression of glucose transporter 1 (GLUT1) at both mRNA and protein levels was observed in DN-MC, leading to increased glucose uptake.
- Activity of glutamine: fructose-6-P aminotransferase (GFAT), a key enzyme in the hexosamine pathway, was elevated in DN-MC, indicating increased glucose flux through this metabolic route.
Impact:
- The study identifies key cellular and metabolic changes in MC that underlie the pathogenesis of diabetic nephropathy.
- These findings highlight MC as a central player in DN development and suggest potential therapeutic targets related to cell growth, matrix production, and glucose metabolism.