All-Trans Retinoic Acid-Preconditioned Mesenchymal Stem Cells Improve Motor Function and Alleviate Tissue Damage After Spinal Cord Injury by Inhibition of HMGB1/NF-κB/NLRP3 Pathway Through Autophagy Activation

Abstract

Spinal cord injury (SCI) is a significant public health issue that imposes numerous burdens on patients and society. Uncontrolled excessive inflammation in the second pathological phase of SCI can aggravate the injury. In this paper, we hypothesized that suppressing inflammatory pathways via autophagy could aid functional recovery, and prevent spinal cord tissue degeneration following SCI. To this end, we examined the effects of intrathecal injection of all-trans retinoic acid (ATRA)-preconditioned bone marrow mesenchymal stem cells (BM-MSCs) (ATRA-MSCs) on autophagy activity and the HMGB1/NF-κB/NLRP3 inflammatory pathway in an SCI rat model. This study demonstrated that SCI increased the expression of Beclin-1 (an autophagy-related gene) and NLRP3 inflammasome components such as NLRP3, ASC, Caspase-1, and pro-inflammatory cytokines IL-1β, IL-18, IL-6, and TNF-α. Additionally, following SCI, the protein levels of key autophagy factors (Beclin-1 and LC3-II) and HMGB1/NF-κB/NLRP3 pathway factors (HMGB1, p-NF-κB, NLRP3, IL-1β, and TNF-α) increased. Our findings indicated that ATRA-MSCs enhanced Beclin-1 and LC3-II levels, regulated the HMGB1/NF-κB/NLRP3 pathway, and inhibited pro-inflammatory cytokines. These factors improved hind limb motor activity and aided in the survival of neurons. Furthermore, ATRA-MSCs demonstrated greater beneficial effects than MSCs in treating spinal cord injury. Overall, ATRA-MSC treatment revealed beneficial effects on the damaged spinal cord by suppressing excessive inflammation and activating autophagy. Further research and investigation of the pathways involved in SCI and the use of amplified stem cells may be beneficial for future clinical use.

Keywords: All-trans retinoic acid; Autophagy; Mesenchymal stem cells; NLRP3 inflammasome; Nuclear factor-kappa B; Spinal cord injury.