Abstract:

Objective： To investigate the effects of sericin on the expressions of c-Jun N-terminal kinase（JNK） signaling pathway-related proteins and of apoptosis of podocytes in the podocytes injury inuced by high glucose，and to clarify the protective effect of sericin and its possible mechanism. Methods The podocytes of immortalized mice with mature differentiation were randomly divided into normal control group（medium containing 5.5 mmol·L^－1glucose）， hypertonic control group（medium containing 30.0 mmol·L^－1 glucose and 24.5 mmol·L^－1mannitol）， high glucose group（medium containing 30.0 mmol·L^－1 glucose）， low concentration of sericin group（medium containing 30.0 mmol·L^－1glucose and 150.0 mg·L^－1sericin）， medium concentration of sericin group（medium containing 30.0 mmol·L^－1 glucose and 300.0 mg·L^－1 sericin），and high concentration of sericin group（medium containing 30.0 mmol·L^－1 glucose and 600.0 mg·L^－1 sericin）.The morphology of podocytes in various groups was observed under optical inverted microscope， real-time fluorescence quantitative PCR（RT-qPCR） method was used to detect the expression levels of podocyte membrane protein（Nephrin），mitogen-activated protein kinase kinase 1（MEKK1）， mitogen-activated protein kinase kinase 4（MKK4），c-Jun N-terminal kinase 1（JNK1） and c-Jun mRNA in the podocytes in various groups，Western blotting method was used to detect the expression levels of Nephrin， MEKK1， MKK4， JNK1， and c-Jun proteins in the podocytes in various groups，and AnnexinⅤ/PI double staining method was used to detect the apoptotic rates of the podocytes in various groups. Results The podocytes in normal control group had larger cell bodies and extended to produce dendritic foot process；compared with normal control group， the body of the podocytes in high glucose group was significantly smaller， the cell spacing was increased， and the number of detached and suspended podocytes was increased；compared with high glucose group， the morphology of the podocytes in different concentrations of sericin groups were gradually tended to be normal.Compared with normal control group，the expression levels of Nephrin mRNA and protein in the podocytes in high glucose group were obviously decreased（P<0.05）， indicating that the podocyte injury model induced by high glucose was successfully established.Compared with normal control group，the expression levels of MEKK1，MKK4，JNK1， and c-Jun mRNA and proteins in the podocytes in high glucose group were significantly increased（P<0.05）.compared with high glucose group，the expression levels of MEKK1， MKK4， JNK1， and c-Jun mRNA and proteins in the podocytes in different concentrations of sericin groups were significantly decreased（P<0.05）；at the same time， the expression levels of MEKK1， MKK4， JNK1， and c-Jun mRNA and proteins in the podocytes in high concentration of sericin group were significantly lower than those in medium concentration of sericin group （P<0.05）， and the expression levels of MEKK1， MKK4， JNK1， and c-Jun mRNA and proteins in the podocytes in medium concentration of sericin group were significantly lower than those in low concentration of sericin group （P<0.05）.Compared with normal control group，the apoptotic rate of the podocytes in high glucose group and hypertonic control group were signifiantly increased（P<0.05）；the apoptotic rates of the podocytes in different concentrations of sericin groups were significantly lower than that in high concentration of sericin group （P<0.05）， and the apoptotic rate of the podocytes in high concentration of sericin group was significantly lower than that in medium concentration of sericin group （P<0.05）， while the apoptotic rate of the podocytes in medium concentration of sericin group was significantly lower than that in low concentration of sericin group （P<0.05）. Conclusion Sericin has protective effect on the podocyte injury induced by high glucose，and its mechanism may be related to its inhibition of the expressions of MEKK1， MKK4， JNK1， and c-Jun in the JNK signaling pathway and its inhibition of the apoptosis of the podocytes.

Key words: Sericin, Podocyte, C-Jun N-terminal kinase signaling pathway, Diabetic nephropathy, Apoptosis