Objective: To observe the morphologic changes and the expression of suppressor of cytokine signaling-1/3 (SOCS-1/3) in renal tubular epithelial cells induced by high glucose (HG) and to investigate their significance.
Methods: The renal tubular epithelial cell line (HKCs) cultured in vitro were divided into blank control group, HG group, and Janus kinase 2 inhibitor AG490 group. HKC of blank control group was cultured for 8 hours in 5.5 mmol/L glucose, and the other two groups were cultured in 300.0 mmol/L glucose or 300.0 mmol/L glucose+10 μmol/L AG490 for 2, 4, 6, 12, 24, 48 hours (n=6). The morphology and ultrastructure were observed with inversion microscope and electron microscope at different time points. Protein expression of SOCS-1/3 was assayed by immunocytochemistry and Western blotting; SOCS-1/3 mRNA was assessed by reverse transcription-polymerase chain reaction (RT-PCR).
Results: Under inversion microscope it was showed that 12 hours after being cultured with HG, the cells assumed a spindle-shape, with irregular protrusions, and cellular membrane became indistinguishable with prolongation of time, with increase of intracellular granules. Under the electron microscope, it was seen that there was distinct decrease in microvilli on the cell membrane and mitochondria, with an increase in rough endoplasmic reticulum. The cellular changes were not obvious in AG490 group. Furthermore, immunocytochemistry and Western blotting showed that the immunoreactivity was localized in the cytoplasm as well as in the nuclei, and there was basic expression of SOCS-1/3 protein in normal HKC (0.218±0.023, 0.337±0.009). HG was shown to induce up-regulation of the expression of SOCS-1/3 protein at 4, 6, 12, 24 hours compared with blank control group. The expression of SOCS-1 was highest at 4 hours (1.022±0.072), and that of SOCS-3 was highest at 6 hours (1.256±0.105, both P<0.01), while the expression of SOCS-1/3 protein in AG490 group was lower than that in HG group (4 hours SOCS-1: 0.589±0.167, 6 hours SOCS-3 : 0.656±0.075, both P<0.05). However, HG induced a higher expression of SOCS-1/3 mRNA at 2, 4, 6, 12 hours compared with blank control group. The expression of SOCS-1 was highest at 4 hours (1.716±0.098 vs. 0.475±0.045, P<0.05), and that of SOCS-3 was highest at 6 hours (2.848±0.116 vs. 0.749±0.086, P<0.01), while the expression of SOCS-1/3 mRNA in AG490 group was lower (4 hours SOCS-1: 0.865±0.075, 6 hours SOCS-3: 0.923±0.116, both P<0.05).
Conclusion: HG could produce morphology and ultrastructure changes in renal tubular epithelial cell, and it induces up-regulation of SOCS-1/3 expression. These changes might be related with negative regulation of Janus kinase (JAK)/signal transducers and activators of transcription (STAT)/SOCS pathway.