Combined Lithium and Noggin Treatment regulates the differentiation of neural progenitor cells in the adult spinal cord and promotes functional recovery after chronic spinal cord injury

Abstract

Background: Inhibition of JAK/STAT and BMP/Smad pathways by LiCl and noggin respectively suppresses astrogenesis and promotes neurogenesis. p300 is found to bridge the STAT-Smad complex signaling. We hypotheses that a combinatory LiCl and Noggin treatment enables concomitant suppression of glial scarring and reactivation of neurogensis and oligodendrogenesis, which leads to functional recovery after chronic SCI. Objectives: To examine whether LiCl and/or noggin can modulate the proliferation and differentiation of NPCs in the injured adult mouse spinal cord, and to examine the effect of the combined treatment on the scar formation, promotion of axonal regeneration and functional recovery in the chronically injured adult spinal cord. Methods: Thoracic spinal cord segment (T8-T10) of 4-6-week-old C57/Bl6 mice were exposed after laminectomy and subjected to a contusion injury. Spinal cord segments were dissected 24 h after contusion injury and prepared for neurosphere culture. Passaged neurosphere cells were grown in differentiation medium with the addition of LiCl (0.5mM-2mM) or noggin (7.5ng/ml-30ng/ml) alone, or a combination of LiCl (1mM) and noggin (15ng/ml) for 7 days. Neurosphere cells were treated with LiCl ± noggin for 4 days before BrdU labeling. Four weeks after the contusion injury, osmotic minipumps delivering treatments (LiCl ± noggin) and vehicle were implanted onto the injured mice for 2 weeks. BMS test was conducted to examine the recovery of locomotor movement 2 hours before the mice were sacrificed. Spinal cord tissue 5mm rostral and caudal apart from the injury epicenter was collected for immunostaining. Results: 1mM of LiCl or 15ng/ml of noggin alone has a maximal effect in promoting both NPC proliferation and differentiation of neurons and oligodendrocytes, while at the same time decreasing astrogenesis. Combined treatment of LiCl and noggin demonstrated a synergistic effect on promoting NPC differentiation along neuronal and oligodendroglial lineage. Combined LiCl and noggin treatment increased the number of immature neurons, mature neurons, oligodendrocyte precursors and oligodendrocytes while decreased the number of astrocytes and microglial cells after chronic SCI. The chronically injured mice treated with combined LiCl and noggin demonstrated significantly better locomotor movement recovery. Conclusion: LiCl and noggin promoted neuronal and oligodendroglial differentiation of adult SC-derived NPCs and at the same time inhibited astroglia differentiation. Combined LiCl and noggin treatment has a synergistic effect on the functional recovery of chronic adult SCI. The mechanism of the synergistic effect is currently under investigation.