LPS-induced inflammatory response triggers cell cycle reactivation in murine neuronal cells through retinoblastoma proteins induction

Cell cycle reactivation in adult neurons is an early hallmark of neurodegeneration. The lipopolysaccharide (LPS) is a well-known pro-inflammatory factor that provokes neuronal cell death via glial cells activation. The retinoblastoma (RB) family includes RB1/p105, retinoblastoma-like 1 (RBL1/p107), and retinoblastoma-like 2 (Rb2/p130). Several studies have indicated that RB proteins exhibit tumor suppressor activities, and play a central role in cell cycle regulation. In this study, we assessed LPS-mediated inflammatory effect on cell cycle reactivation and apoptosis of neuronally differentiated cells. Also, we investigated whether the LPS-mediated inflammatory response can influence the function and expression of RB proteins. Our results showed that LPS challenges triggered cell cycle reactivation of differentiated neuronal cells, indicated by an accumulation of cells in S and G2/M phase. Furthermore, we found that LPS treatment also induced apoptotic death of neurons. Interestingly, we observed that LPS-mediated inflammatory effect on cell cycle re-entry and apoptosis was concomitant with the aberrant expression of RBL1/p107 and RB1/p105. To the best of our knowledge, our study is the first to indicate a role of LPS in inducing cell cycle re-entry and/or apoptosis of differentiated neuronal cells, perhaps through mechanisms altering the expression of specific members of RB family proteins. This study provides novel information on the biology of post-mitotic neurons and could help in identifying novel therapeutic targets to prevent de novo cell cycle reactivation and/or apoptosis of neurons undergoing neurodegenerative processes.