Akt/PKB isoforms expression in the human lumbar herniated disc: correlation with clinical and MRI findings

Intervertebral disc (IVD) degeneration suggests a complex process influenced by genetics, lifestyle and biomechanics, which accounts for the development of low back pain (LBP) and lumbar radiculopathy, a major cause of musculoskeletal disability in humans. The family of Akt/PKB kinases is a principal mediator in the signal transduction pathways, which contribute to transcriptional regulation, cell growth, proliferation, apoptosis, and survival ability. The purpose of this study was to evaluate the transcriptional profile of the AKT family genes in human herniated discs and the involvement of the PI3K-Akt signaling pathway in human IVD degeneration. Real-time PCR analysis was used to assess the mRNA expression pattern of the three Akt/PKB isoforms in 63 herniated and 10 control disc specimens. Our results showed a significant positive correlation between AKT1 and AKT3 mRNA in herniated discs suggesting a synergistic action between these isoforms in disc herniation. Interestingly, AKT2 mRNA was up-regulated in patients with acute pain during the first 12 months, indicating that AKT2 transcriptional activation may be associated with acute rather than chronic inflammation and phagocytosis. Finally, Akt1/PKB transcription presented a stepwise activation as disc herniation deteriorated. Our findings provide evidence on the transcriptional activation of the Akt/PKB pathway indicating that it is involved in lumbar disc degeneration. There is need for further studies to elucidate the exact role and down-stream signaling action of Akt/PKB isoforms in the pathogenesis of lumbar disc herniation.