Insulin-Like Growth Factor 1 Activates PI3k/Akt Signaling to Antagonize Lumbar Disc Degeneration

The pathogenesis of Lumbar disc degeneration (LDD) has been extensively studied in the past. In particular, a role of matrix metalloproteinase 3 (MMP3) in the disease initiation and progression has been recently reported. However, an involvement of Insulin-like growth factor 1 (IGF-I)-stimulated phosphatidylinositol-3 kinase (PI3k) / Akt signaling pathway-mediated control of MMP3 in LDD has not been acknowledged.

We examined the serum IGF-1 levels and activation of the receptor for IGF-1 (IGF-1R) in resected discs in patients with LDD, compared to the fractured discs from traumatized, non-LDD subjects as a control. We analyzed the effects of IGF-1 on the activation of IGF-1R, Akt and MMP3 in a human nucleus pulposus SV40 cell line (HNPSV). We transfected HNPSV cells with a constitutive nuclear FoxO1, and analyzed its effect on the activation of IGF-1R, Akt and MMP3.

LDD patients had significantly lower levels of serum IGF-1, and LDD discs had significantly lower levels of activated IGF-1R. IGF-1 induced phosphorylation of IGF-1R, and then phosphorylation of its downstream factor Akt in the HNPSV cells, resulting in significantly inhibition of MMP3. Further, FoxO1 nuclear retention completely abolished the inhibitory effects of IGF-1 on MMP3 in HNPSV cells.

Together, IGF-1/Akt/FoxO1/MMP3 regulatory machinery may control the development of LDD.