Lydon, Katherine L.

ABSTRACT Premature physeal closure occurs following trauma, cancer, or infection. Current treatments have poor success rates. With recent pediatric donor tissue availability, physeal allograft transfer (PAT) can now be considered. The purpose of this study was to study the safety and feasibility of PAT in a large animal model. The aim of this study is to gather foundational data to inform future studies into the efficacy of PAT. Physeal defects were created in the distal femur of nine female domestic swine and treated with PAT from two male donor pigs, cementation, or bone autograft. Viability was assessed. After 3 months, physes were visualized using CT and MRI. Integration, tissue composition, donor DNA presence, and microscopic appearance were evaluated. Physeal allografts demonstrated 93% viability after procurement and preservation. All animals reached the 3‐months study endpoint without gross deformations. No physeal bars formed in any group. Cystic changes were seen in experimental and control femurs. All groups showed disorganized tissue architecture without growth plate recapitulation. High allografts viability and structural integrity after procurement support the potential of this treatment. Although no gross deformities were found, transferred physes demonstrate poor integration and incomplete repair. The lack of physeal bar formation in the control group limits the reliability of the animal model for studying physeal allograft transfer. Lastly, this study was designed as a feasibility study and lacks power to compare treatment effects statistically. The efficacy of PAT for preventing growth arrest remains undetermined.

Objective This proof-of-concept study investigated an improved cell-based injection therapy combining mesenchymal stem cells (MSCs) and meniscus cells (MCs) to support superior meniscus allograft repopulation and early revival compared to injecting MSCs alone. Design In this controlled laboratory study, frozen meniscus allograft samples were injected vertically with a cell suspension containing different ratios of MSCs and MCs or control (lactated ringers) and cultured for 28 days. Samples were analyzed weekly for cell viability, migration, and metabolism using histological and biochemical assays. Tissue medium was analyzed for matrix metalloproteinase (MMP) expression using zymography. Results Cellular repopulation of frozen allografts injected with different cell suspensions was validated by immunohistochemistry. Significant higher DNA content was evidenced in grafts treated with suspensions of MCs or MC:MSC (1:4 ratio). Cell metabolic activity was significantly different between all treated groups and control group after 1 week. Allografts injected with MCs showed significantly more cell proliferation than injections with MSCs. MMP2 activity was detected in medium of all grafts cellularized with MCs with or without MSCs. Scanning electron microscopy (SEM) analysis showed resolution of the needle puncture, but not in the control group. Cell labeling of MCs upon injection of mixed MC:MSC suspensions revealed a gradual increase in the cell ratio. Conclusions The findings of this study establish that injection of MCs with or without MSCs enhances the cellularity of meniscus allograft to support early graft revival and remodeling.

Background: Fresh-frozen allografts are the current standard in meniscal allograft transplant (MAT) surgery, due to their availability, ease of preservation, and affordability. However, fresh-frozen grafts are associated with several clinical challenges such as graft shrinkage and extrusion, among many others. Purpose: To present the current knowledge on the use of fresh meniscal allografts, presenting whether benefits associated with fresh grafts provide sufficient evidence to support their use in clinical practice. Study Design: Systematic review; Level of evidence, 5. Methods: A comprehensive search was conducted with keywords listed below. After an initial screening on title and abstract, full-text articles were assessed with the inclusion criteria. Results: A total of 78 studies matched the inclusion criteria. Literature and preclinical studies indicated that fresh meniscal allografts are beneficial for maintaining mechanical properties, graft ultrastructure, and matrix metabolism due to the presence of viable cells. Therefore, fresh allografts may address common complications associated with fresh-frozen MAT. To overcome challenges associated with both fresh-frozen and fresh allografts, a group has studied treating fresh-frozen allografts with a cell-based injection therapy. Conclusion: Fresh meniscal allografts pose several challenges including limited availability, demanding preservation procedures, and high costs. Although the role of viable cells within meniscal allografts remains controversial, these cells may be vital for maintaining tissue properties.

Matrix stiffness is a central regulator of fibroblast function. However, the transcriptional mechanisms linking matrix stiffness to changes in fibroblast phenotype are incompletely understood. Here, we evaluated the effect of matrix stiffness on genome-wide chromatin accessibility in freshly isolated lung fibroblasts using ATAC-seq. We found higher matrix stiffness profoundly increased global chromatin accessibility relative to lower matrix stiffness, and these alterations were in close genomic proximity to known profibrotic gene programs. Motif analysis of these regulated genomic loci identified ZNF416 as a putative mediator of fibroblast stiffness responses. Genome occupancy analysis using ChIP-seq confirmed that ZNF416 occupies a broad range of genes implicated in fibroblast activation and tissue fibrosis, with relatively little overlap in genomic occupancy with other mechanoresponsive and profibrotic transcriptional regulators. Using loss- and gain-of-function studies, we demonstrated that ZNF416 plays a critical role in fibroblast proliferation, extracellular matrix synthesis, and contractile function. Together, these observations identify ZNF416 as novel mechano-activated transcriptional regulator of fibroblast biology.