Using a Transection Paradigm to Enhance the Repair Mechanisms of an Investigational Human Cell Therapy

Abstract

One promising strategy in cell therapies for Parkinson’s disease (PD) is to harness a patient’s own cells to provide neuroprotection in areas of the brain affected by neurodegeneration. No treatment exists to replace cells in the brain. Thus, our goal has been to support sick neurons and slow neurodegeneration by transplanting living repair tissue from the peripheral nervous system into the substantia nigra of those with PD. Our group has pioneered the transplantation of transection-activated sural nerve fascicles into the brain of human subjects with PD. Our experience in sural nerve transplantation has supported the safety and feasibility of this approach. As part of a paradigm to assess the reparative properties of human sural nerve following a transection injury, we collected nerve tissue approximately 2 weeks after sural nerve transection for immunoassays from 15 participants, and collected samples from two additional participants for single nuclei RNA sequencing. We quantified the expression of key neuroprotective and select anti-apoptotic genes along with their corresponding protein levels using immunoassays. The single nuclei data clustered into 10 distinctive groups defined on the basis of previously published cell type-specific genes. Transection-induced reparative peripheral nerve tissue showed RNA expression of neuroprotective factors and anti-apoptotic factors across multiple cell types after nerve injury induction. Key proteins of interest (BDNF, GDNF, beta-NGF, PDGFB, and VEGF) were upregulated in reparative tissue. These results provide insight on this repair tissue’s utility as a neuroprotective cell therapy.

Transection injury differentially alters the proteome of the human sural nerve

“…Classic Schwann cell markers in our mass spectrometry analysis such as S100B [ 52 ], MAG, MPZ, ERBB3, PLP1 all showed a significant downregulation by t-test (q ≤ 0.05), but failed to meet the Z ≥ |2| (log2) criterion (see raw data) suggesting in aggregate, a reduction in these markers. Our previous single nuclei RNA sequencing work supports our current data and demonstrates MPZ , MBP , and MAG downregulation two weeks after injury [ 47 ]. After the first step of degeneration which is clearing the myelin [ 9 ], Schwann cells then de-differentiate into more progenitor/stem cell-like phenotype.…”

“…Two weeks after injury, we observed higher mean levels in the injury samples compared to the naïve samples of growth factors: BDNF, CDNF, VEGF, GDNF, NGF, PDGF-AA and PDGF-BB ( Fig 5B ). These results align with our single nuclei RNA sequencing work in which the mRNA of these factors are present after peripheral nerve injury [ 47 ]. The protein-level profile of individual neuroprotective factors can vary greatly with time.…”

“…Schwann cells transform from the myelinating phenotype to a reparative phenotype via EMT mechanisms [ 28 , 45 ]. Single nuclei RNA sequencing demonstrates the presence of a repair Schwann cell marker, NGFR upregulated after injury [ 47 ]. Additionally, the EMT GO pathway (GO: 0001837) includes two DEAD-Box Helicase 5 (DDX) genes including DEAD-Box Helicase 5 (DDX5, also known as p68) and DEAD-Box Helicase 17 (DDX17) which are upregulated after injury.…”

Recipient Reaction and Composition of Autologous Sural Nerve Tissue Grafts into the Human Brain

“…Neurotrophic factors, produced by both Schwann cells and fibroblasts found in peripheral nerve tissues and which we identified in the grafts, can aid in reducing the effects of disease or injury to the brain [53], providing one potential mechanism by which PNT could be effective in increasing neuronal survival in PD or in AD. Direct evidence for GDNF and its family ligands in Iba1-positive glial cells has also been shown [54], demonstrating that several of the growth factors produced by cells within the PNT [23] could directly affect the activation of both astrocytes and microglia in the brain in a regeneration-positive manner. Future strategies to assess the efficacy of the graft on cell survival may include assessment of the viability of efferent nerve fibers from the targeted nucleus; for example, the projections from the SN to the posterior putamen following PNT engraftment.…”

“…More recent studies support the idea that peripheral nerve tissue grafts, containing fibroblasts, Schwann cells, and mesenchymal stem cells, can also provide a powerful continuous secretion of a cocktail of anti-inflammatory, pro-regenerative, neuroprotective, and growth factors needed for neuronal survival [10,22,23]. However, the host response, including activation of innate immune cells in the brain, can be detrimental to allogeneic transplants; for example, of stem cells [24][25][26][27].…”