Jesus Acevedo Cintron
Program: Developmental Regenerative and Stem Cell Biology
Current advisor: Susan Mackinnon, MD
Undergraduate university: University of Puerto Rico-Rio Piedras
Research summary
Peripheral nerve injuries (PNI) result in severe disability and loss of quality of life, whilst promoting regeneration after repair remains a challenge. Therefore, development of therapies to improve nerve regeneration is critical. To that end, one of the most severe injuries to nerve causes a gap between nerve ends, requiring a complex process to regenerate the entire missing nerve segment. Acellular nerve allografts (ANAs) have been used as an off-the-shelf product to repair nerve gap injuries. However, regeneration across ANAs is length dependent, where increasing ANA length correlating with decreased regeneration. The mechanisms causing decreased regeneration across longer grafts is still undetermined. While the roles of the inflammatory and immune responses in nerve regeneration have been well established, for nerve grafts, such as ANAs, less is known. However, in ANAs, alteration to the immune response can lead to poor regeneration. Therefore, the overall aim of this research was to identify changes in the regenerative and inflammatory microenvironment of ANAs across different timepoints and identify how modulation of the immune system alters nerve regeneration across long ANAs.
In the first aim, we examined changes in the axons, blood vessels and cytokines of short and long ANAs after repair assessing changes in the regenerative microenvironment as regeneration progressed. Short (2 cm) ANAs were used as a model of robust regeneration while long (4 cm) ANAs were used as a model for poor or failed regeneration. Morphometric histology was used to assess regeneration and changes to the vasculature, while gene expression analysis was used to measure changes in cytokine expression within the ANAs. This study suggested poor axonal regeneration across long ANAs coincided with changes in the morphology of blood vessels and the development of a pro-inflammatory microenvironment across long ANAs.
In the second aim, we identified differences in the transcriptome profile of short and long ANAs and used immunosuppressant tacrolimus (FK506) to modulate the microenvironment of long ANAs. Bulk-RNA sequencing was used for a global assessment of the regenerative microenvironment of ANAs by analyzing the transcriptome profile of all cells present. Transcriptome analysis of short and long ANAs revealed upregulation of immune and metabolic processes in the long versus short ANAs. This further supports the hypothesis long ANAs are immunologically more active but also suggested the microenvironment within long ANAs was more degradative. Due to the upregulation of immune processes in long ANAs, FK506 was used to observe if modulation of the immune response and promotion of axonal elongation improves nerve regeneration across long ANAs. Morphometric histology and muscle force analysis revealed FK506 improves regeneration and functional recovery across long ANAs. Furthermore, using bulk-RNA sequencing we demonstrated FK506 alters the immune and regenerative microenvironment within long ANAs. This work demonstrated immunosuppression while promoting axonal elongation mechanisms in synergy are needed to improve regeneration across long ANAs.
Graduate publications
Acevedo Cintrón JA, Hunter DA, Schellhardt L, Pan D, Mackinnon SE, Wood MD. 2024 Limited Nerve Regeneration across Acellular Nerve Allografts (ANAs) Coincides with Changes in Blood Vessel Morphology and the Development of a Pro-Inflammatory Microenvironment. Int J Mol Sci, 25(12):6413.
Liebendorfer A, Finnan MJ, Schofield JB, Pinni SL, Acevedo-Cintrón JA, Schellhardt L, Snyder-Warwick AK, Mackinnon SE, Wood MD. 2023 Loss of Gata1 decreased eosinophils, macrophages, and type 2 cytokines in regenerating nerve and delayed axon regeneration after a segmental nerve injury. Exp Neurol, 362():114327.
Pan D, Schellhardt L, Acevedo-Cintron JA, Hunter D, Snyder-Warwick AK, Mackinnon SE, Wood MD. 2022 IL-4 expressing cells are recruited to nerve after injury and promote regeneration. Exp Neurol, 347():113909.
Sayanagi J, Acevedo-Cintrón JA, Pan D, Schellhardt L, Hunter DA, Snyder-Warwick AK, Mackinnon SE, Wood MD. 2021 Brief Electrical Stimulation Accelerates Axon Regeneration and Promotes Recovery Following Nerve Transection and Repair in Mice. J Bone Joint Surg Am, 103(20):e80.
Pan D, Sayanagi J, Acevedo-Cintrón JA, Schellhardt L, Snyder-Warwick AK, Mackinnon SE, Wood MD. 2021 Liposomes embedded within fibrin gels facilitate localized macrophage manipulations within nerve. J Neurosci Methods, 348():108981.
Pan D, Acevedo-Cintrón JA, Sayanagi J, Snyder-Warwick AK, Mackinnon SE, Wood MD. 2020 The CCL2/CCR2 axis is critical to recruiting macrophages into acellular nerve allograft bridging a nerve gap to promote angiogenesis and regeneration. Exp Neurol, 331():113363.