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Gu X, Rahman FS, Bendale G, Tran B, Miyata JF, Hernandez A, Anand S, Romero-Ortega MI. Pleiotrophin-Neuregulin1 promote axon regeneration and sorting in conduit repair of critical nerve gap injuries. RESEARCH SQUARE 2023:rs.3.rs-3429258. [PMID: 37986821 PMCID: PMC10659554 DOI: 10.21203/rs.3.rs-3429258/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Significant challenges remain in the treatment of critical nerve gap injuries using artificial nerve conduits. We previously reported successful axon regeneration across a 40 mm nerve gap using a biosynthetic nerve implant (BNI) with multi-luminal synergistic growth factor release. However, axon sorting, remyelination, and functional recovery were limited. Neuregulin1 (NRG1) plays a significant role in regulating the proliferation and differentiation of Schwann cells (SCs) during development and after injury. We hypothesize that the release of NRG1 type III combined with pleiotrophin (PTN) in the BNI will enhance axon growth, remyelination, and function of regenerated nerves across a critical gap. A rabbit 40 mm peroneal gap injury model was used to investigate the therapeutic efficacy of BNIs containing either NRG1, PTN, or PTN+NRG1 growth factor release. We found that NRG1 treatment doubled the number of regenerated axons (1276±895) compared to empty controls (633±666) and PTN tripled this number (2270±989). NRG1 also significantly increased the number of SOX10+ Schwann cells in mid-conduit (20.42%±11.78%) and reduced the number of abnormal Remak axon bundles. The combination of PTN+NRG1 increased axon diameter (1.70±1.06) vs control (1.21±0.77) (p<0.01), with 15.35% of axons above 3 μm, comparable to autograft. However, the total number of remyelinated axons was not increased by the added NRG1 release, which correlated with absence of axonal NRG1 type III expression in the regenerated axons. Electrophysiological evaluation showed higher muscle force recruitment (23.8±16.0 mN vs 17.4±1.4 mN) and maximum evoked compound motor action potential (353 μV vs 37 μV) in PTN-NRG1 group versus control, which correlated with the improvement in the toe spread recovery observed in PTN-NRG1 treated animals (0.64±0.02) vs control (0.50±0.01). These results revealed the need of a combination of pro-regenerative and remyelinating growth factor combination therapy for the repair of critical nerve gaps.
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Affiliation(s)
- Xingjian Gu
- Department of Biomedical Engineering, University of Houston, Houston TX 77204
| | - Farial S. Rahman
- Department of Biomedical Engineering, University of Houston, Houston TX 77204
| | - G Bendale
- Department of Biomedical Engineering, University of Houston, Houston TX 77204
| | - B Tran
- Department of Biomedical Engineering, University of Houston, Houston TX 77204
| | - JF Miyata
- Department of Biomedical Engineering, University of Houston, Houston TX 77204
| | - A Hernandez
- Department of Biomedical Engineering, University of Houston, Houston TX 77204
| | - S Anand
- Department of Biomedical Engineering, University of Houston, Houston TX 77204
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Leach GA, Dean RA, Kumar NG, Tsai C, Chiarappa FE, Cederna PS, Kung TA, Reid CM. Regenerative Peripheral Nerve Interface Surgery: Anatomic and Technical Guide. PLASTIC AND RECONSTRUCTIVE SURGERY-GLOBAL OPEN 2023; 11:e5127. [PMID: 37465283 PMCID: PMC10351954 DOI: 10.1097/gox.0000000000005127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Accepted: 06/06/2023] [Indexed: 07/20/2023]
Abstract
Regenerative peripheral nerve interface (RPNI) surgery has been demonstrated to be an effective tool as an interface for neuroprosthetics. Additionally, it has been shown to be a reproducible and reliable strategy for the active treatment and for prevention of neuromas. The purpose of this article is to provide a comprehensive review of RPNI surgery to demonstrate its simplicity and empower reconstructive surgeons to add this to their armamentarium. This article discusses the basic science of neuroma formation and prevention, as well as the theory of RPNI. An anatomic review and discussion of surgical technique for each level of amputation and considerations for other etiologies of traumatic neuromas are included. Lastly, the authors discuss the future of RPNI surgery and compare this with other active techniques for the treatment of neuromas.
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Affiliation(s)
- Garrison A. Leach
- From the Department of General Surgery, Division of Plastic Surgery, University of California San Diego, La Jolla, Calif
| | - Riley A. Dean
- From the Department of General Surgery, Division of Plastic Surgery, University of California San Diego, La Jolla, Calif
| | - Nishant Ganesh Kumar
- Section of Plastic and Reconstructive Surgery and the Department of Biomedical Engineering, University of Michigan, Ann Arbor, Mich
| | - Catherine Tsai
- From the Department of General Surgery, Division of Plastic Surgery, University of California San Diego, La Jolla, Calif
| | - Frank E. Chiarappa
- Department of Orthopedic Surgery, University of California San Diego, La Jolla, Calif
| | - Paul S. Cederna
- Section of Plastic and Reconstructive Surgery and the Department of Biomedical Engineering, University of Michigan, Ann Arbor, Mich
| | - Theodore A. Kung
- Section of Plastic and Reconstructive Surgery and the Department of Biomedical Engineering, University of Michigan, Ann Arbor, Mich
| | - Chris M. Reid
- From the Department of General Surgery, Division of Plastic Surgery, University of California San Diego, La Jolla, Calif
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3D culture of the spinal cord with roots as an ex vivo model for comparative studies of motor and sensory nerve regeneration. Exp Neurol 2023; 362:114322. [PMID: 36652972 DOI: 10.1016/j.expneurol.2023.114322] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 12/21/2022] [Accepted: 01/13/2023] [Indexed: 01/18/2023]
Abstract
Motor and sensory nerves exhibit tissue-specific structural and functional features. However, in vitro models designed to reflect tissue-specific differences between motor and sensory nerve regeneration have rarely been reported. Here, by embedding the spinal cord with roots (SCWR) in a 3D hydrogel environment, we compared the nerve regeneration processes between the ventral and dorsal roots. The 3D hydrogel environment induced an outward migration of neurons in the gray matter of the spinal cord, which allowed the long-term survival of motor neurons. Tuj1 immunofluorescence labeling confirmed the regeneration of neurites from both the ventral and dorsal roots. Next, we detected asymmetric ventral and dorsal root regeneration in response to nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF), and we observed motor and sensory Schwann cell phenotypes in the regenerated ventral and dorsal roots, respectively. Moreover, based on the SCWR model, we identified a targeted effect of collagen VI on sensory nerve fasciculation and characterized the protein expression profiles correlating to motor/sensory-specific nerve regeneration. These results suggest that the SCWR model can serve as a valuable ex vivo model for comparative study of motor and sensory nerve regeneration and for pharmacodynamic evaluations.
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Contreras E, Bolívar S, Navarro X, Udina E. New insights into peripheral nerve regeneration: The role of secretomes. Exp Neurol 2022; 354:114069. [DOI: 10.1016/j.expneurol.2022.114069] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 02/05/2022] [Accepted: 04/03/2022] [Indexed: 11/04/2022]
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Xu C, Hong Y. Rational design of biodegradable thermoplastic polyurethanes for tissue repair. Bioact Mater 2021; 15:250-271. [PMID: 35386346 PMCID: PMC8940769 DOI: 10.1016/j.bioactmat.2021.11.029] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 11/09/2021] [Accepted: 11/24/2021] [Indexed: 12/25/2022] Open
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Guedan-Duran A, Jemni-Damer N, Orueta-Zenarruzabeitia I, Guinea GV, Perez-Rigueiro J, Gonzalez-Nieto D, Panetsos F. Biomimetic Approaches for Separated Regeneration of Sensory and Motor Fibers in Amputee People: Necessary Conditions for Functional Integration of Sensory-Motor Prostheses With the Peripheral Nerves. Front Bioeng Biotechnol 2020; 8:584823. [PMID: 33224936 PMCID: PMC7670549 DOI: 10.3389/fbioe.2020.584823] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Accepted: 09/25/2020] [Indexed: 12/22/2022] Open
Abstract
The regenerative capacity of the peripheral nervous system after an injury is limited, and a complete function is not recovered, mainly due to the loss of nerve tissue after the injury that causes a separation between the nerve ends and to the disorganized and intermingled growth of sensory and motor nerve fibers that cause erroneous reinnervations. Even though the development of biomaterials is a very promising field, today no significant results have been achieved. In this work, we study not only the characteristics that should have the support that will allow the growth of nerve fibers, but also the molecular profile necessary for a specific guidance. To do this, we carried out an exhaustive study of the molecular profile present during the regeneration of the sensory and motor fibers separately, as well as of the effect obtained by the administration and inhibition of different factors involved in the regeneration. In addition, we offer a complete design of the ideal characteristics of a biomaterial, which allows the growth of the sensory and motor neurons in a differentiated way, indicating (1) size and characteristics of the material; (2) necessity to act at the microlevel, on small groups of neurons; (3) combination of molecules and specific substrates; and (4) temporal profile of those molecules expression throughout the regeneration process. The importance of the design we offer is that it respects the complexity and characteristics of the regeneration process; it indicates the appropriate temporal conditions of molecular expression, in order to obtain a synergistic effect; it takes into account the importance of considering the process at the group of neuron level; and it gives an answer to the main limitations in the current studies.
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Affiliation(s)
- Atocha Guedan-Duran
- Neuro-computing and Neuro-robotics Research Group, Complutense University of Madrid, Madrid, Spain
- Innovation Group, Institute for Health Research San Carlos Clinical Hospital (IdISSC), Madrid, Spain
- Department of Biomedical Engineering, Tufts University, Medford, MA, United States
| | - Nahla Jemni-Damer
- Neuro-computing and Neuro-robotics Research Group, Complutense University of Madrid, Madrid, Spain
- Innovation Group, Institute for Health Research San Carlos Clinical Hospital (IdISSC), Madrid, Spain
| | - Irune Orueta-Zenarruzabeitia
- Neuro-computing and Neuro-robotics Research Group, Complutense University of Madrid, Madrid, Spain
- Innovation Group, Institute for Health Research San Carlos Clinical Hospital (IdISSC), Madrid, Spain
| | - Gustavo Víctor Guinea
- Center for Biomedical Technology, Universidad Politécnica de Madrid, Madrid, Spain
- Department of Material Science, Civil Engineering Superior School, Universidad Politécnica de Madrid, Madrid, Spain
- Biomedical Research Networking Center in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Madrid, Spain
- Silk Biomed SL, Madrid, Spain
| | - José Perez-Rigueiro
- Center for Biomedical Technology, Universidad Politécnica de Madrid, Madrid, Spain
- Department of Material Science, Civil Engineering Superior School, Universidad Politécnica de Madrid, Madrid, Spain
- Biomedical Research Networking Center in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Madrid, Spain
- Silk Biomed SL, Madrid, Spain
| | - Daniel Gonzalez-Nieto
- Center for Biomedical Technology, Universidad Politécnica de Madrid, Madrid, Spain
- Biomedical Research Networking Center in Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Madrid, Spain
- Silk Biomed SL, Madrid, Spain
| | - Fivos Panetsos
- Neuro-computing and Neuro-robotics Research Group, Complutense University of Madrid, Madrid, Spain
- Innovation Group, Institute for Health Research San Carlos Clinical Hospital (IdISSC), Madrid, Spain
- Silk Biomed SL, Madrid, Spain
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Bizzi E, Ajemian R. From motor planning to execution: a sensorimotor loop perspective. J Neurophysiol 2020; 124:1815-1823. [PMID: 33052779 DOI: 10.1152/jn.00715.2019] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
How is an evanescent wish to move translated into a concrete action? This simple question and puzzling miracle remains a focal point of motor systems neuroscience. Where does the difficulty lie? A great deal has been known about biomechanics for quite some time. More recently, there have been significant advances in our understanding of how the spinal system is organized into modules corresponding to spinal synergies, which are fixed patterns of multimuscle recruitment. But much less is known about how the supraspinal system recruits these synergies in the correct spatiotemporal pattern to effectively control movement. We argue that what makes the problem of supraspinal control so difficult is that it emerges as a result of multiple convergent and redundant sensorimotor loops. Because these loops are convergent, multiple modes of information are mixed before being sent to the spinal system; because they are redundant, information is overlapping such that a mechanism must exist to eliminate the redundancy before the signal is sent to the spinal system. Given these complex interactions, simple correlation analyses between movement variables and neural activity are likely to render a confusing and inconsistent picture. Here, we suggest that the perspective of sensorimotor loops might help in achieving a better systems-level understanding. Furthermore, state-of-the-art techniques in neurotechnology, such as optogenetics, appear to be well suited for investigating the problem of motor control at the level of loops.
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Affiliation(s)
- Emilio Bizzi
- McGovern Institute for Brain Research and Department of Brain and Cognitive Science, Massachusetts Institute of Technology, Cambridge, Massachusetts
| | - Robert Ajemian
- McGovern Institute for Brain Research and Department of Brain and Cognitive Science, Massachusetts Institute of Technology, Cambridge, Massachusetts
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Xu C, Okpokwasili C, Huang Y, Shi X, Wu J, Liao J, Tang L, Hong Y. Optimizing Anisotropic Polyurethane Scaffolds to Mechanically Match with Native Myocardium. ACS Biomater Sci Eng 2020; 6:2757-2769. [PMID: 33313394 PMCID: PMC7725265 DOI: 10.1021/acsbiomaterials.9b01860] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Biodegradable cardiac patch is desirable to possess mechanical properties mimicking native myocardium for heart infarction treatment. We fabricated a series of anisotropic and biodegradable polyurethane porous scaffolds via thermally induced phase separation (TIPS) and tailored their mechanical properties by using various polyurethanes with different soft segments and varying polymer concentrations. The uniaxial mechanical properties, suture retention strength, ball-burst strength, and biaxial mechanical properties of the anisotropic porous scaffolds were optimized to mechanically match native myocardium. The optimal anisotropic scaffold had a ball burst strength (20.7 ± 1.5 N) comparable to that of native porcine myocardium (20.4 ± 6.0 N) and showed anisotropic behavior close to biaxial stretching behavior of the native porcine myocardium. Furthermore, the optimized porous scaffold was combined with a porcine myocardium-derived hydrogel to form a biohybrid scaffold. The biohybrid scaffold showed morphologies similar to the decellularized porcine myocardial matrix. This combination did not affect the mechanical properties of the synthetic scaffold alone. After in vivo rat subcutaneous implantation, the biohybrid scaffolds showed minimal immune response and exhibited higher cell penetration than the polyurethane scaffold alone. This biohybrid scaffold with biomimetic mechanics and good tissue compatibility would have great potential to be applied as a biodegradable acellular cardiac patch for myocardial infarction treatment.
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Affiliation(s)
- Cancan Xu
- Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
- Joint Biomedical Engineering Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Chuka Okpokwasili
- Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
- Joint Biomedical Engineering Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Yihui Huang
- Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
- Joint Biomedical Engineering Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Xiaodan Shi
- Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
- Joint Biomedical Engineering Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Jinglei Wu
- Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
- Joint Biomedical Engineering Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Jun Liao
- Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
- Joint Biomedical Engineering Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Liping Tang
- Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
- Joint Biomedical Engineering Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Yi Hong
- Department of Bioengineering, University of Texas at Arlington, Arlington, TX 76019, USA
- Joint Biomedical Engineering Program, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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Porzionato A, Barbon S, Stocco E, Dalzoppo D, Contran M, De Rose E, Parnigotto PP, Macchi V, Grandi C, De Caro R. Development of Oxidized Polyvinyl Alcohol-Based Nerve Conduits Coupled with the Ciliary Neurotrophic Factor. MATERIALS (BASEL, SWITZERLAND) 2019; 12:E1996. [PMID: 31234386 PMCID: PMC6631399 DOI: 10.3390/ma12121996] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Revised: 06/09/2019] [Accepted: 06/19/2019] [Indexed: 12/14/2022]
Abstract
Functionalized synthetic conduits represent a promising strategy to enhance peripheral nerve regeneration by guiding axon growth while delivering therapeutic neurotrophic factors. In this work, hollow nerve conduits made of polyvinyl alcohol partially oxidized with bromine (OxPVA_Br2) and potassium permanganate (OxPVA_KMnO4) were investigated for their structural/biological properties and ability to absorb/release the ciliary neurotrophic factor (CNTF). Chemical oxidation enhanced water uptake capacity of the polymer, with maximum swelling index of 60.5% ± 2.5%, 71.3% ± 3.6% and 19.5% ± 4.0% for OxPVA_Br2, OxPVA_KMnO4 and PVA, respectively. Accordingly, hydrogel porosity increased from 15.27% ± 1.16% (PVA) to 62.71% ± 8.63% (OxPVA_Br2) or 77.50% ± 3.39% (OxPVA_KMnO4) after oxidation. Besides proving that oxidized PVA conduits exhibited mechanical resistance and a suture holding ability, they did not exert a cytotoxic effect on SH-SY5Y and Schwann cells and biodegraded over time when subjected to enzymatic digestion, functionalization with CNTF was performed. Interestingly, higher amounts of neurotrophic factor were detected in the lumen of OxPVA_Br2 (0.22 ± 0.029 µg) and OxPVA_KMnO4 (0.29 ± 0.033 µg) guides rather than PVA (0.11 ± 0.021 µg) tubular scaffolds. In conclusion, we defined a promising technology to obtain drug delivery conduits based on functionalizable oxidized PVA hydrogels.
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Affiliation(s)
- Andrea Porzionato
- Department of Neurosciences, Section of Human Anatomy, University of Padova, Via A. Gabelli 65, 35121 Padova, Italy.
- L.i.f.e.L.a.b. Program, Consorzio per la Ricerca Sanitaria (CORIS), Veneto Region, Via N. Giustiniani 2, 35128 Padova, Italy.
| | - Silvia Barbon
- Department of Neurosciences, Section of Human Anatomy, University of Padova, Via A. Gabelli 65, 35121 Padova, Italy.
- L.i.f.e.L.a.b. Program, Consorzio per la Ricerca Sanitaria (CORIS), Veneto Region, Via N. Giustiniani 2, 35128 Padova, Italy.
| | - Elena Stocco
- Department of Neurosciences, Section of Human Anatomy, University of Padova, Via A. Gabelli 65, 35121 Padova, Italy.
- L.i.f.e.L.a.b. Program, Consorzio per la Ricerca Sanitaria (CORIS), Veneto Region, Via N. Giustiniani 2, 35128 Padova, Italy.
| | - Daniele Dalzoppo
- Department of Pharmaceutical and Pharmacological Sciences, University of Padova, Via F. Marzolo 5, 35128 Padova, Italy.
| | - Martina Contran
- Department of Neurosciences, Section of Human Anatomy, University of Padova, Via A. Gabelli 65, 35121 Padova, Italy.
| | - Enrico De Rose
- Department of Neurosciences, Section of Human Anatomy, University of Padova, Via A. Gabelli 65, 35121 Padova, Italy.
| | - Pier Paolo Parnigotto
- Foundation for Biology and Regenerative Medicine, Tissue Engineering and Signaling (T.E.S.) Onlus, 35030 Padua, Italy.
| | - Veronica Macchi
- Department of Neurosciences, Section of Human Anatomy, University of Padova, Via A. Gabelli 65, 35121 Padova, Italy.
- L.i.f.e.L.a.b. Program, Consorzio per la Ricerca Sanitaria (CORIS), Veneto Region, Via N. Giustiniani 2, 35128 Padova, Italy.
| | - Claudio Grandi
- Department of Pharmaceutical and Pharmacological Sciences, University of Padova, Via F. Marzolo 5, 35128 Padova, Italy.
| | - Raffaele De Caro
- Department of Neurosciences, Section of Human Anatomy, University of Padova, Via A. Gabelli 65, 35121 Padova, Italy.
- L.i.f.e.L.a.b. Program, Consorzio per la Ricerca Sanitaria (CORIS), Veneto Region, Via N. Giustiniani 2, 35128 Padova, Italy.
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Alsmadi NZ, Bendale GS, Kanneganti A, Shihabeddin T, Nguyen AH, Hor E, Dash S, Johnston B, Granja-Vazquez R, Romero-Ortega MI. Glial-derived growth factor and pleiotrophin synergistically promote axonal regeneration in critical nerve injuries. Acta Biomater 2018; 78:165-177. [PMID: 30059799 DOI: 10.1016/j.actbio.2018.07.048] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2018] [Revised: 07/16/2018] [Accepted: 07/27/2018] [Indexed: 12/14/2022]
Abstract
The repair of nerve gap injuries longer than 3 cm is limited by the need to sacrifice donor tissue and the morbidity associated with the autograft gold standard, while decellularized grafts and biodegradable conduits are effective only in short nerve defects. The advantage of isogenic nerve implants seems to be the release of various growth factors by the denervated Schwann cells. We evaluated the effect of vascular endothelial growth factor, neurotrophins, and pleiotrophin (PTN) supplementation of multi-luminal conduits, in the repair of 3 and 4 cm nerve gaps in the rabbit peroneal nerve. In vitro screening revealed a synergistic regenerative effect of PTN with glial-derived neurotrophic factor (GDNF) in promoting sensory axon density, and motor axonal growth from spinal cord explants. In vivo, pleiotrophins were able to support nerve regrowth across a 3 cm gap. In the 4 cm lesions, PTN-GDNF had a modest effect in the number of axons distal to the implant, while increasing the mean axon diameter (1 ± 0.4; p ≤ 0.001) over PTN or GDNF alone (0.80 ± 0.2, 0.84 ± 0.5; respectively). Some regenerated axons reinnervated muscle targets as indicated by neuromuscular junction staining. However, many were wrapped in Remak bundles, suggesting a delay in axonal sorting, explaining the limited electrophysiological function of the reinnervated muscle, and the modest recovery in toe spreading in the PTN-GDNF repaired animals. These results support the use of synergistic neurotrophic/pleiotrophic growth factors in long gap repair and underscore the need for re-myelination strategies distal to the injury site. STATEMENT OF SIGNIFICANCE Nerve injuries due to trauma or tumor resection often result in long gaps that are challenging to repair. The best clinical option demands the use of autologous grafts that are associated with serious side effects. Bioengineered nerves are considered a good alternative, particularly if supplemented with growth factors, but current options do not match the regenerative capacity of autografts. This study revealed the synergistic effect of neurotrophins and pleiotrophins designed to achieve a broad cellular regenerative effect, and that GDNF-PTN are able to mediated axonal growth and partial functional recovery in a 4 cm nerve gap injury, albeit delays in remyelination. This report underscores the need for defining an optimal growth factor support for biosynthetic nerve implants.
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