Melittin Inducing the Apoptosis of Renal Tubule Epithelial Cells through Upregulation of Bax/Bcl-2 Expression and Activation of TNF-α Signaling Pathway

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-α (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-α. 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-αlevel 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-α 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-α signaling pathway.