Induction of functional erythropoietin and erythropoietin receptor gene expression by gamma-aminobutyric acid and piperine in kidney epithelial cells

Abstract

Aims: The aim of this study was to evaluate gamma-aminobutyric acid (GABA)- and piperine-induced erythropoietin (EPO) and EPO-receptor expression.

Materials and methods: The effect of GABA and piperine on cell viability was examined using kidney epithelial cells. Expression levels of EPO and EPO-R mRNA and protein were evaluated in response to GABA and piperine treatments. GABA- and piperine-mediated activation of the mitogen-activated protein kinase (MAPK) signaling pathway was investigated. Additionally, EPO function was evaluated using conditioned media containing EPO. The GABA receptor type involved in this process was identified.

Key findings: Messenger RNA and protein expression levels of EPO and EPO-R significantly increased in response to treatment with GABA, piperine, or the combination of both, compared with control. GABA plus piperine synergistically enhanced EPO and EPO-R expression through p38 and c-Jun N-terminal kinase (JNK) MAPK signaling pathways, but not through the extracellular signal-regulated kinase (ERK) MAPK pathway. SB203580 and SP600125 (p38 and JNK pathway inhibitors, respectively) attenuated GABA plus piperine-induced EPO and EPO-R expression. Treatment of macrophages with EPO-containing conditioned media induced mRNA expression of interleukin (IL)-10 and nuclear factor (NF)-κB due to the interaction between EPO and EPO-R. Interestingly, GABA-induced EPO and EPO-R expression was mediated through GABA_A, not GABA_B, receptor activation.

Significance: These findings demonstrate that GABA plus piperine-mediated p38 and JNK MAPK activation increases EPO and EPO-R expression, resulting in up-regulation of IL-10 and NF-κB.

Keywords: Erythropoietin; Gamma-aminobutyric acid; MAPK; Piperine; Signal transduction.