Melittin inducing the apoptosis of renal tubule epithelial cells through upregulation of Bax/Bcl-2 expression and activation of TNF- Signaling pathway

Abstract

Background. Acute kidney injury (AKI) caused by bee stings is common, with characteristics of acute onset, severe illness, and high mortality. Melittin, a major component of bee venom, has been considered to play a key role in bee sting related AKI. This study aims to illustrate whether melittin could lead to apoptosis of renal tubular epithelial cells (RTECs) and to investigate its mechanism. Methods. In vivo, 45 mice were randomly divided into the melittin group (n=30, injected with melittin into the tail vein according to the total dose of 4.0 ug/g weight) and the control group (n=15, injected with the same volume of saline into the tail vein). In vitro, human RTECs (HK-2) were cultured and treated with melittin (2ug/ml or 4ug/ml) and TNF- (10ng/ml). Biochemical analysis, HE stains, and electron microscope were performed to evaluate renal function and pathological changes. TUNEL stains and flow cytometry were performed to detect apoptosis. Real-time PCR was performed to detect mRNA levels of Bax, Bcl-2, and TNF-. Simple western assay and immunohistochemical (IH) and immunofluorescent (IF) stains were performed for protein detection. Results. Melittin successfully induced AKI in mice. Compared with the control group, obvious injury and apoptosis of RTECs were observed in the melittin group; the mRNA and protein expressions of Bax were significantly increased, while the expression of Bcl-2 was significantly decreased. The serum TNF-level in melittin group was significantly higher than that in control group. In vitro, the results confirmed that melittin can cause HK-2 cells apoptosis. The trends of expression of Bax and Bcl-2 were consistent with the results in vivo. The levels of TNF- mRNA and protein by PCR and Western blot were significantly higher in melittin group than those in control group. Conclusion. Melittin can lead to the apoptosis of RTECs, which may be mediated by upregulating the expression of Bax/Bcl-2 and activating the TNF- signaling pathway.