Efficacy of Nerve-Derived Hydrogels to Promote Axon Regeneration Is Influenced by the Method of Tissue Decellularization.

Injuries to large peripheral nerves are often associated with tissue defects and require reconstruction using autologous nerve grafts, which have limited availability and result in donor site morbidity. Peripheral nerve-derived hydrogels could potentially supplement or even replace these grafts. In this study, three decellularization protocols based on the ionic detergents sodium dodecyl sulfate (P1) and sodium deoxycholate (P2), or the organic solvent tri-n-butyl phosphate (P3), were used to prepare hydrogels. All protocols resulted in significantly decreased amounts of genomic DNA, but the P2 hydrogel showed the best preservation of extracellular matrix proteins, cytokines, and chemokines, and reduced levels of sulfated glycosaminoglycans. In vitro P1 and P2 hydrogels supported Schwann cell viability, secretion of VEGF, and neurite outgrowth. Surgical repair of a 10 mm-long rat sciatic nerve gap was performed by implantation of tubular polycaprolactone conduits filled with hydrogels followed by analyses using diffusion tensor imaging and immunostaining for neuronal and glial markers. The results demonstrated that the P2 hydrogel considerably increased the number of axons and the distance of regeneration into the distal nerve stump. In summary, the method used to decellularize nerve tissue affects the efficacy of the resulting hydrogels to support regeneration after nerve injury.

Water jet-assisted lipoaspiration and Sepax cell separation system for the isolation of adipose stem cells with high adipogenic potential.

INTRODUCTION: Water jet-assisted liposuction has gained popularity due to favourable fat grafting outcomes. In this study, we compared stem cells obtained from fat isolated with manual or the water jet-assisted procedure. METHODS: Liposuction of abdominal fat was performed using the two methods on each donor (n = 10). Aspirate samples were collagenase digested and the isolated cells seeded in vitro prior to proliferation, adipogenic differentiation and angiogenic activity analyses. RESULTS: Cells from either procedure proliferated at similar rates and exhibited a similar colony-forming ability. The cells expressed stem cell markers CD73, CD90 and CD105. In the water jet cell preparations, there were higher numbers of cells expressing CD146. Robust adipogenic differentiation was observed in cultures expanded from both manual and water jet lipoaspirates. Gene analysis showed higher expression of the adipocyte markers aP2 and GLUT4 in the adipocyte-differentiated water jet cell preparations, and ELISA indicated increased secretion of adiponectin from these cells. Both cell groups expressed vasculogenic factors and the water jet cells promoted the highest levels of in vitro angiogenesis. Given these positive results, we further characterised the water jet cells when prepared using an automated closed cell processing unit, the Sepax-2 system (Cytiva). The growth and stem cell properties of the Sepax-processed cells were similar to the standard centrifugation protocol, but there was evidence for greater adipogenic differentiation in the Sepax-processed cells. CONCLUSIONS: Water jet lipoaspirates yield cells with high adipogenic potential and angiogenic activity, which may be beneficial for use in cell-assisted lipotransfers.

Evaluation of growth, stemness, and angiogenic properties of dental pulp stem cells cultured in cGMP xeno-/serum-free medium.

This study was aimed to investigate the effects of cGMP xeno-/serum-free medium (XSF, Irvine Scientific) on the properties of human dental pulp stem cells (DPSCs). DPSCs, from passage 2, were cultured in XSF or fetal bovine serum (FBS)-supplemented medium, and sub-cultured up to passage 8. Cumulative population doublings (PDs) and the number of colony-forming-units (CFUs) were determined. qRT-PCR, ELISA, and in vitro assays were used to assess angiogenic capacity. Flow cytometry was used to measure CD73, CD90, and CD105 expression. Differentiation into osteo-, adipo-, and chondrogenic cell lineages was performed. DPSCs showed more elongated morphology, a reduced rate of proliferation at later passages, and lower CFU counts in XSF compared with FBS. Expression of angiogenic factors at the gene and protein levels varied in the two media and with passage number, but cells grown in XSF had more in vitro angiogenic activity. The majority of early and late passage DPSCs cultured in XSF expressed CD73 and CD90. In contrast, the percentage of CD105 positive DPSCs in XSF medium was significantly lower with increased passage whereas the majority of cells cultured in FBS were CD105 positive. Switching XSF-cultured DPSCs to medium supplemented with human serum restored the expression of CD105. The tri-lineage differentiation of DPSCs cultured under XSF and FBS conditions was similar. We showed that despite reduced CD105 expression levels, DPSCs expanded in XSF medium maintained a functional MSC phenotype. Furthermore, restoration of CD105 expression is likely to occur upon in vivo transplantation, when cells are exposed to human serum.

Long-Term Effects of Fibrin Conduit with Human Mesenchymal Stem Cells and Immunosuppression after Peripheral Nerve Repair in a Xenogenic Model.

INTRODUCTION: Previously we showed that a fibrin glue conduit with human mesenchymal stem cells (hMSCs) and cyclosporine A (CsA) enhanced early nerve regeneration. In this study long term effects of this conduit are investigated. METHODS: In a rat model, the sciatic nerve was repaired with fibrin conduit containing fibrin matrix, fibrin conduit containing fibrin matrix with CsA treatment and fibrin conduit containing fibrin matrix with hMSCs and CsA treatment, and also with nerve graft as control. RESULTS: At 12 weeks 34% of motoneurons of the control group regenerated axons through the fibrin conduit. CsA treatment alone or with hMSCs resulted in axon regeneration of 67% and 64% motoneurons respectively. The gastrocnemius muscle weight was reduced in the conduit with fibrin matrix. The treatment with CsA or CsA with hMSCs induced recovery of the muscle weight and size of fast type fibers towards the levels of the nerve graft group. DISCUSSION: The transplantation of hMSCs for peripheral nerve injury should be optimized to demonstrate their beneficial effects. The CsA may have its own effect on nerve regeneration.

Effects of a defined xeno-free medium on the growth and neurotrophic and angiogenic properties of human adult stem cells.

BACKGROUND: The growth properties and neurotrophic and angiogenic effects of human mesenchymal stromal cells (MSCs) cultured in a defined xeno-free, serum-free medium (MesenCult-XF) were investigated. METHODS: Human MSCs from adipose tissue (ASCs) and bone marrow (BMSCs) were cultured in Minimum Essential Medium-alpha (α-MEM) containing fetal calf serum or in MesenCult-XF. Proliferation was measured over 10 passages and the colony-forming unit (CFU) assay and expression of cluster of differentiation (CD) surface markers were determined. Neurite outgrowth and angiogenic activity of the MSCs were determined. RESULTS: At early passage, both ASCs and BMSCs showed better proliferation in MesenCult-XF compared with standard α-MEM-containing serum. However, CFUs were significantly lower in MesenCult-XF. ASCs cultured in MesenCult-XF continued to expand at faster rates than cells grown in serum. BMSCs showed morphological changes at late passage in MesenCult-XF and stained positive for senescence ß-galactosidase activity. Expression levels of CD73 and CD90 were similar in both cell types under the various culture conditions but CD105 was significantly reduced at passage 10 in MesenCult-XF. In vitro stimulation of the cells enhanced the expression of brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF-A) and angiopoietin-1. Stimulated ASCs grown in MesenCult-XF evoked the longest neurite outgrowth in a neuron co-culture model. Stimulated BMSCs grown in MesenCult-XF produced the most extensive network of capillary-like tube structures in an in vitro angiogenesis assay. CONCLUSIONS: ASCs and BMSCs exhibit high levels of neurotrophic and angiogenic activity when grown in the defined serum-free medium indicating their suitability for treatment of various neurological conditions. However, long-term expansion in MesenCult-XF might be restricted to ASCs.

Aging effect on neurotrophic activity of human mesenchymal stem cells.

Clinical efficacy of stem cells for nerve repair is likely to be influenced by issues including donor age and in vitro expansion time. We isolated human mesenchymal stem cells (MSC) from bone marrow of young (16-18 years) and old (67-75 years) donors and analyzed their capacity to differentiate and promote neurite outgrowth from dorsal root ganglia (DRG) neurons. Treatment of MSC with growth factors (forskolin, basic fibroblast growth factor, platelet derived growth factor-AA and glial growth factor-2) induced protein expression of the glial cell marker S100 in cultures from young but not old donors. MSC expressed various neurotrophic factor mRNA transcripts. Growth factor treatment enhanced the levels of BDNF and VEGF transcripts with corresponding increases in protein release in both donor cell groups. MSC in co-culture with DRG neurons significantly enhanced total neurite length which, in the case of young but not old donors, was further potentiated by treatment of the MSC with the growth factors. Stem cells from young donors maintained their proliferation rate over a time course of 9 weeks whereas those from the old donors showed increased population doubling times. MSC from young donors, differentiated with growth factors after long-term culture, maintained their ability to enhance neurite outgrowth of DRG. Therefore, MSC isolated from young donors are likely to be a favourable cell source for nerve repair.

Fibrin conduit supplemented with human mesenchymal stem cells and immunosuppressive treatment enhances regeneration after peripheral nerve injury.

To address the need for the development of bioengineered replacement of a nerve graft, a novel two component fibrin glue conduit was combined with human mesenchymal stem cells (MSC) and immunosupressive treatment with cyclosporine A. The effects of MSC on axonal regeneration in the conduit and reaction of activated macrophages were investigated using sciatic nerve injury model. A 10mm gap in the sciatic nerve of a rat was created and repaired either with fibrin glue conduit containing diluted fibrin matrix or fibrin glue conduit containing fibrin matrix with MSC at concentration of 80×10(6) cells/ml. Cells were labeled with PKH26 prior to transplantation. The animals received daily injections of cyclosporine A. After 3 weeks the distance of regeneration and area occupied by regenerating axons and ED1 positives macrophages was measured. MSC survived in the conduit and enhanced axonal regeneration only when transplantation was combined with cyclosporine A treatment. Moreover, addition of cyclosporine A to the conduits with transplanted MSC significantly reduced the ED1 macrophage reaction.

Neuroprotective and growth-promoting effects of bone marrow stromal cells after cervical spinal cord injury in adult rats.

BACKGROUND AIMS: Bone marrow stromal cells (BMSC) have been shown to provide neuroprotection after transplantation into the injured central nervous system. The present study investigated whether adult rat BMSC differentiated along a Schwann cell lineage could increase production of trophic factors and support neuronal survival and axonal regeneration after transplantation into the injured spinal cord. METHODS: After cervical C4 hemi-section, 5-bromo-2-deoxyuridine (BrdU)/green fluorescent protein (GFP)-labeled BMSC were injected into the lateral funiculus at 1 mm rostral and caudal to the lesion site. Spinal cords were analyzed 2-13 weeks after transplantation. RESULTS AND CONCLUSIONS: Treatment of native BMSC with Schwann cell-differentiating factors significantly increased production of brain-derived neurotrophic factor in vitro. Transplanted undifferentiated and differentiated BMSC remained at the injection sites, and in the trauma zone were often associated with neurofilament-positive fibers and increased levels of vascular endothelial growth factor. BMSC promoted extensive in-growth of serotonin-positive raphaespinal axons and calcitonin gene-related peptide (CGRP)-positive dorsal root sensory axons into the trauma zone, and significantly attenuated astroglial and microglial cell reactions, but induced aberrant sprouting of CGRP-immunoreactive axons in Rexed's lamina III. Differentiated BMSC provided neuroprotection for axotomized rubrospinal neurons and increased the density of rubrospinal axons in the dorsolateral funiculus rostral to the injury site. The present results suggest that BMSC induced along the Schwann cell lineage increase expression of trophic factors and have neuroprotective and growth-promoting effects after spinal cord injury.

Characterisation of human mesenchymal stem cells following differentiation into Schwann cell-like cells.

Cell-based therapies provide a clinically applicable and available alternative to nerve autografts. Our previous studies have characterised rat-derived mesenchymal stem cells (MSC) and here we have investigated the phenotypic, molecular and functional characteristics of human-derived MSC (hMSC) differentiated along a Schwann cell lineage. The hMSC were isolated from healthy human donors and the identity of the undifferentiated hMSC was confirmed by the detection of MSC specific cells surface markers. The hMSC were differentiated along a glial cell lineage using an established cocktail of growth factors including glial growth factor-2. Following differentiation, the hMSC expressed the key Schwann cell (SC) markers at both the transcriptional and translational level. More importantly, we show the functional effect of hMSC on neurite outgrowth using an in vitro co-culture model system with rat-derived primary sensory neurons. The number of DRG sprouting neurites was significantly enhanced in the presence of differentiated hMSC; neurite length and density (branching) were also increased. These results provide evidence that hMSC can undergo molecular, morphological and functional changes to adopt a SC-like behaviour and, therefore, could be suitable as SC substitutes for nerve repair in clinical applications.

Biodegradable poly-beta-hydroxybutyrate scaffold seeded with Schwann cells to promote spinal cord repair.

Cavity formation is an important obstacle impeding regeneration after spinal cord injury and bridging strategies are essential to provide physical substrate allowing axons to grow across the lesion site. In this study we evaluated effects of biodegradable tubular conduit made from poly-beta-hydroxybutyrate (PHB) scaffold with predominantly unidirectional fiber orientation and supplemented with cultured adult Schwann cells on axonal regeneration after cervical spinal cord injury in adult rats. After transplantation into the injured spinal cord, plain PHB conduit was well-integrated into posttraumatic cavity and induced modest astroglial reaction. Regenerating axons were found mainly outside the PHB with only single fibers crossing the host-graft interface. No host Schwann cells migrated into the graft. In contrast, when suspension of adult Schwann cells was added to the PHB during transplantation, neurofilament-positive axons filled the conduit and became associated with the implanted cells. Although rubrospinal fibers did not enter the PHB, numerous raphaespinal and CGRP-positive axons were found within the conduit. Modification of PHB surface with fibronectin, laminin or collagen significantly increased Schwann cell attachment and proliferation in vitro. However, transplantation of PHB conduit pre-coated with fibronectin and seeded with Schwann cells did not alter axonal growth response. The results demonstrate that a PHB scaffold promotes attachment, proliferation and survival of adult Schwann cells and supports marked axonal regeneration within the graft.