Tissue-engineered grafts exploit axon-facilitated axon regeneration and pathway protection to enable recovery after 5-cm nerve defects in pigs.

Functional restoration following major peripheral nerve injury (PNI) is challenging, given slow axon growth rates and eventual regenerative pathway degradation in the absence of axons. We are developing tissue-engineered nerve grafts (TENGs) to simultaneously "bridge" missing nerve segments and "babysit" regenerative capacity by providing living axons to guide host axons and maintain the distal pathway. TENGs were biofabricated using porcine neurons and "stretch-grown" axon tracts. TENG neurons survived and elicited axon-facilitated axon regeneration to accelerate regrowth across both short (1 cm) and long (5 cm) segmental nerve defects in pigs. TENG axons also closely interacted with host Schwann cells to maintain proregenerative capacity. TENGs drove regeneration across 5-cm defects in both motor and mixed motor-sensory nerves, resulting in dense axon regeneration and electrophysiological recovery at levels similar to autograft repairs. This approach of accelerating axon regeneration while maintaining the pathway for long-distance regeneration may achieve recovery after currently unrepairable PNIs.

Tissue Engineered Axon Tracts Serve as Living Scaffolds to Accelerate Axonal Regeneration and Functional Recovery Following Peripheral Nerve Injury in Rats.

Strategies to accelerate the rate of axon regeneration would improve functional recovery following peripheral nerve injury, in particular for cases involving segmental nerve defects. We are advancing tissue engineered nerve grafts (TENGs) comprised of long, aligned, centimeter-scale axon tracts developed by the controlled process of axon "stretch-growth" in custom mechanobioreactors. The current study used a rat sciatic nerve model to investigate the mechanisms of axon regeneration across nerve gaps bridged by TENGs as well as the extent of functional recovery compared to nerve guidance tubes (NGT) or autografts. We established that host axon growth occurred directly along TENG axons, which mimicked the action of "pioneer" axons during development by providing directed cues for accelerated outgrowth. Indeed, axon regeneration rates across TENGs were 3-4 fold faster than NGTs and equivalent to autografts. The infiltration of host Schwann cells - traditional drivers of peripheral axon regeneration - was also accelerated and progressed directly along TENG axons. Moreover, TENG repairs resulted in functional recovery levels equivalent to autografts, with both several-fold superior to NGTs. These findings demonstrate that engineered axon tracts serve as "living scaffolds" to guide host axon outgrowth by a new mechanism - which we term "axon-facilitated axon regeneration" - that leads to enhanced functional recovery.

Human Adipose Stromal/Stem Cells from Obese Donors Show Reduced Efficacy in Halting Disease Progression in the Experimental Autoimmune Encephalomyelitis Model of Multiple Sclerosis.

Multiple sclerosis is an autoimmune disease that affects the white matter of the central nervous system and involves inflammation and demyelination. The recent advances in our understanding of adipose-derived stromal/stem cells (ASCs) and the utilization of these cells in clinical settings to treat diseases have made it essential to identify the most effective ASCs for therapy. Studies have not yet investigated the impact of obesity on the therapeutic efficacy of ASCs. Obesity is characterized by adipocyte hyperplasia and hypertrophy and can extend to metabolic and endocrine dysfunction. Investigating the impact obesity has on ASC biology will determine whether these cells are suitable for use in regenerative medicine. The therapeutic efficacy of ASCs isolated from lean subjects (body mass index [BMI] < 25; lnASCs) and obese subjects (BMI > 30; obASCs) were determined in murine experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. Compared with the EAE disease-modifying effects of lnASCs, obASCs consistently failed to alleviate clinical symptoms or inhibit inflammation in the central nervous system. When activated, obASCs expressed higher mRNA levels of several pro-inflammatory cytokines compared with lnASCs. Additionally, conditioned media (CM) collected from the obASCs markedly enhanced the proliferation and differentiation of T cells; whereas, CM from lnASC did not. These results indicate that obesity reduces, or eliminates, the anti-inflammatory effects of human ASCs such that they may not be a suitable cell source for the treatment of autoimmune diseases. The data suggest that donor demographics may be particularly important when identifying suitable stem cells for treatment.