The rapid increase in painful intervertebral disc (IVD) degeneration (IDD) makes it an urgent need to provide solutions for preventing IDD and promoting its regeneration. IDD is associated with loss of IVD cellularity, matrix degradation and apoptosis, and identifying specific targets to prevent these aspects of IDD would open the door for novel and specific treatments. Recently, the PH domain leucine-rich repeat protein phosphatase 1 (PHLPP1) was identified as key player in insulin resistance, obesity and osteoarthritis. Importantly, effects of PHLPP1 in healthy and disease are highly context-specific. In insulin resistant patients, PHLPP1 induces glycogen synthesis via activation of glycogen synthase kinase 3?, (GSK3?) which is expressed at high levels in NPs, and has been correlated to apoptosis and matrix degradation, suggesting a tissue-specific PHLPP1 mechanism in IVDs. PHLPP1 has not been investigated in IVDs and we, for the first time, show higher PHLPP1 expression in degenerated human IVDs and injured mice IVDs. And demonstrate that PHLPP1 knockout increased NP cellularity in mice. Our goal is to determine the specific contributions of PHLPP1 to IDD and to identify the feasibility of PHLPP1 as novel target to stop IDD progression. This study has high impact because of the high impact of IDD and feasibility of translation, yet there are some risks because nothing is known about the role of PHLPP1 in IDD. The proposed studies will test the overall hypothesis that PHLPP1 is a key player in inducing IDD. We hypothesize that PHLPP1 presence will cause apoptosis and matrix degradation while its absence will induce cell proliferation and matrix production. We believe that PHLPP1 regulates IDD via the PTEN/PI3K/AKT and PKC pathways and that targeting PHLPP1 will prevent the progression of IDD.
Aim 1 will determine the role of PHLPP1 depletion on IDD progression using in vivo PHLPP1-ko mice on healthy and injured IVDs with measurements of IVD morphology, structure, and cellularity.
Aim 2 will determine the relationship between PHLPP1 expression and human IDD by determining PHLPP1 expression in human IVDs from autopsy and correlating this with degenerative grade.
Aim 3 will determine the efficacy of specific blocking agents for inhibiting PHLPP1 activity and inducing cell proliferation and matrix production using human IVD cells taken from autopsy specimens. Blocking studies will evaluate if PHLPP1 act via AKT and PKC signaling by assessing several downstream molecules of these pathways. This project is highly significant because the major burden of IDD in the United States. Investigating PHLPP1 and its role in IDD is very innovative because PHLPP1 has never been explored in IVD research. The outcome of this proposal is highly impactful because if PHLPP1 could be identified as a therapeutic target; further studies could be performed to translate this knowledge into minimal invasive treatment strategies for millions of people suffering from IDD in the United States and Worldwide.
Painful intervertebral disc degeneration is a major public health concern with few minimally invasive and effective treatments available. This study identifies specific roles for phosphatase PHLPP1 in intervertebral disc degeneration, as implicated our preliminary data, using combined mouse knock-out and human autopsy and cell culture studies. These studies are high impact because PHLPP1 has not been investigated in disc degeneration and is a druggable target with high translational potential.