Regenerative Rehabilitation: Combining Stem Cell Therapies and Activity-Dependent Stimulation

Brain-derived neurotrophic factor/tropomyosin receptor kinase B signaling in spinal muscular atrophy and amyotrophic lateral sclerosis

Tropomyosin receptor kinase B (TrkB) and its primary ligand brain-derived neurotrophic factor (BDNF) are expressed in the neuromuscular system, where they affect neuronal survival, differentiation, and functions. Changes in BDNF levels and full-length TrkB (TrkB-FL) signaling have been revealed in spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS), two common forms of motor neuron diseases that are characterized by defective neuromuscular junctions in early disease stages and subsequently progressive muscle weakness. This review summarizes the current understanding of BDNF/TrkB-FL-related research in SMA and ALS, with an emphasis on their alterations in the neuromuscular system and possible BDNF/TrkB-FL-targeting therapeutic strategies. The limitations of current studies and future directions are also discussed, giving the hope of discovering novel and effective treatments.

How can clinical safety and efficacy concerns in stem cell therapy for spinal cord injury be overcome?

INTRODUCTION

Spinal cord injury (SCI) can lead to severe neurological dysfunction. Despite scientific and medical advances, clinically effective regenerative therapies including stem cells are lacking for SCI.

AREAS COVERED

This paper discusses translational challenges related to the safe, effective use of stem cells for SCI, with a focus on mesenchymal stem cells (MSCs), neural stem cells (NSCs), Schwann cells (SCs), olfactory ensheathing cells (OECs), oligodendrocyte precursor cells (OPCs), embryonic stem cells (ESCs), and induced pluripotent stem cells (iPSCs). We discuss approaches to enhance the efficacy of cell-based strategies by i) addressing patient heterogeneity and enhancing patient selection; ii) selecting cell type, cell source, cell developmental stage, and delivery technique; iii) enhancing graft integration and mitigating immune-mediated graft rejection; and iv) ensuring availability of cells. Additionally, we review strategies to optimize outcomes including combinatorial use of rehabilitation and discuss ways to mitigate potential risks of tumor formation associated with stem cell-based strategies.

EXPERT OPINION

Basic science research will drive translational advances to develop stem cell-based therapies for SCI. Genetic, serological, and imaging biomarkers may enable individualization of cell-based treatments. Moreover, combinatorial strategies will be required to enhance graft survival, migration and functional integration, to enable precision-based intervention.

The Safety and Effectiveness of Early, Progressive Weight Bearing and Implant Choice after Traumatic Lower Extremity Fracture: A Systematic Review

The goal of this systematic review was to examine existing evidence on the effectiveness of early, progressive weight bearing on patients after traumatic lower extremity fractures and relate these findings to device/implant choice. A search of the literature in PubMed/Medline, Embase, Web of Science, and the Cochrane Library was performed through January 2022. Randomized controlled trials and non-randomized, prospective longitudinal investigations of early, progressive weight bearing in skeletally mature adults after traumatic lower extremity fracture were included in the search, with 21 publications included in the final analysis. A summary of the loading progressions used in each study, along with the primary and additional outcomes, is provided. The progression of weight bearing was variable, dependent on fracture location and hardware fixation; however, overall outcomes were good with few complications. Most studies scored "high" on the bias tools and were predominately performed without physical therapist investigators. Few studies have investigated early, progressive weight bearing in patients after traumatic lower extremity fractures. The available clinical evidence provides variable progression guidelines. Relatively few complications and improved patient function were observed in this review. More research is needed from a rehabilitation perspective to obtain graded progression recommendations, informed by basic science concepts and tissue loading principles.

An Adaptive Assistance Controller to Optimize the Exoskeleton Contribution in Rehabilitation

In this paper, we present a novel adaptation rule to optimize the exoskeleton assistance in rehabilitation tasks. The proposed method adapts the exoskeleton contribution to user impairment severity without any prior knowledge about the user motor capacity. The proposed controller is a combination of an adaptive feedforward controller and a low gain adaptive PD controller. The PD controller guarantees the stability of the human-exoskeleton system during feedforward torque adaptation by utilizing only the human-exoskeleton joint positions as the sensory feedback for assistive torque optimization. In addition to providing a convergence proof, in order to study the performance of our method we applied it to a simplified 2-DOF model of human-arm and a generic 9-DOF model of lower limb to perform walking. In each simulated task, we implemented the impaired human torque to be insufficient for the task completion. Moreover, the scenarios that violate our convergence proof assumptions are considered. The simulation results show a converging behavior for the proposed controller; the maximum convergence time of 20 s is observed. In addition, a stable control performance that optimally supplements the remaining user motor contribution is observed; the joint angle tracking error in steady condition and its improvement compared to the start of adaptation are as follows: shoulder 0.96±2.53° (76%); elbow −0.35±0.81° (33%); hip 0.10±0.86° (38%); knee −0.19±0.67° (25%); and ankle −0.05±0.20° (60%). The presented simulation results verify the robustness of proposed adaptive method in cases that differ from our mathematical assumptions and indicate its potentials to be used in practice.

Effectiveness of mesenchymal stem cells for treating patients with knee osteoarthritis: a meta-analysis toward the establishment of effective regenerative rehabilitation

This systematic review with a meta-analysis aimed to summarize the current evidence of the effectiveness of mesenchymal stem cell (MSC) treatment for knee osteoarthritis (OA) and to examine whether rehabilitation is an effect modifier of the effect estimate of MSC treatment. A literature search yielded 659 studies, of which 35 studies met the inclusion criteria (n = 2385 patients; mean age: 36.0-74.5 years). The meta-analysis results suggested that MSC treatment through intra-articular injection or arthroscopic implantation significantly improved knee pain (standardized mean difference [SMD]: -1.45, 95% confidence interval [CI]: -1.94, -0.96), self-reported physical function (SMD: 1.50, 95% CI: 1.09, 1.92), and cartilage quality (SMD: -1.99; 95% CI: -3.51, -0.47). However, the MSC treatment efficacy on cartilage volume was limited (SMD: 0.49; 95% CI: -0.19, 1.16). Minor adverse events (knee pain or swelling) were reported with a wide-ranging prevalence of 2-60%; however, no severe adverse events occurred. The evidence for these outcomes was "very low" to "low" according to the Grades of Recommendation, Assessment, Development and Evaluation system because of the poor study design, high risk of bias, large heterogeneity, and wide 95% CI of the effects estimate. Performing rehabilitation was significantly associated with better SMD for self-reported physical function (regression coefficient: 0.881, 95% CI: 0.049, 1.712; P = 0.039). We suggest that more high quality randomized controlled trials with consideration of the potential rehabilitation-driven clinical benefit would be needed to facilitate the foundation of effective MSC treatment and regenerative rehabilitation for patients with knee OA.