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Summary:. Systemic scleroderma is a chronic connective tissue disease characterized by internal organ and skin fibrosis. Unfortunately, there is a lack of efficacious treatments for cutaneous manifestations, and alternative interventions should be considered. Fat grafting has gained significant attention due to its regenerative properties and success in improving skin quality and volume deficits in fibrotic diseases. While some studies have investigated the efficacy of autologous fat grafting, we utilized the Coleman method for harvesting and processing to determine the efficacy of fat grafting to improve skin fibrosis in the hands and face of scleroderma patients without excess processing of adipose tissue. Patients with a diagnosis of scleroderma who underwent fat grafting between March 2015 and March 2019 at the University of Michigan were included. Ten female patients were identified that met inclusion criteria. The mean age at the time of surgery was 48.7 (± 17.6) years. An average of 53.2 (± 15.5) ml of fat was injected into the hands and 26.1 (± 16.4) ml into the face. Patients were treated with 1–4 rounds of grafting depending on the initial severity of skin fibrosis and volume deficiency. Fat grafting subjectively and qualitatively improved perioral skin quality, facial animation, hand range of motion, and hand pain for patients with systemic scleroderma. No complications were identified. Additional studies are necessary to determine the ideal volume, timing of treatments, and type of fat to optimize the efficacy of autologous fat grafting for the treatment of systemic scleroderma.

Purpose: Existing literature describes the interdependence between neurotrophic and vascular signals in the central nervous system. We hypothesize a similar crosstalk important to extremity healing involving the peripheral nervous system and angiogenic cells. Nerves are difficult to capture via axons found in the periphery alone. Thus, we have interrogated from publicly available single-nuclei transcriptomic data of peripheral nerve soma (dorsal root ganglia), injured by physical transection or chemically induced pain. We present a combined analysis of extremity polytrauma (burn/tenotomy HO model) and peripheral nerve (post-injury/pain DRG model) to determine if there is expression of vascular signals by nerves and reciprocal neurotrophic signals by cells local to the injury site. Methods: A 30% dorsal burn and Achilles transection was performed in C57/BL6J mice. The tendon site tissues were harvested from baseline (t0) and day 7, 42 after induction. Samples were prepared for library generation on a 10x Genomics Chromium Controller, sequenced on a Illumina HiSeq 4000, and analyzed with Cell Ranger Software for pre-processing and alignment to the mm10 genome. DRG analyses and clusters were abstracted from NIH-GEO (GSE154659). Downstream analyses including unsupervised clustering downstream analyses were performed with Seurat. Results: We first examined candidate neurotrophins and vascular signals in nerve (DRG), finding robust upregulation of Bdnf and Vegfa. In HO, the site of injury contains many cells that may potentially respond to these signals. Indeed, in sequencing data from the pre-HO anlagen, endothelium and smooth muscle cell populations express upregulation for receptors to the nerve-derived Vegfa via Flt1/VEGFR1. This population in addition to being sensitive to the VEGFA ligand, also demonstrates upregulation of Ngf, signifying a potential vasculo-neuro axis where a vascular signal induces endothelium/SMCs to produce neurotrophic signals. Completing the circuit, the original DRG cells and by logical extension, regenerating peripheral nerves, are highly enriched for the neurotrophin receptors: Ntrk1/TrkA (responsive to the SMC derived NGF), Ntrk2/TrkB (responsive to the nerve-autonomous BDNF), and Ntrk3/TrkC (partial combined NGF/BDNF response). This potentially signifies a feedforward loop where peripheral nerve induces angiogenesis which in return, promotes nascent nerve ingrowth in a cyclical process. Indeed, in targeted knockout of a local VEGFA source (VegfaPrrx1 mice), the injury site demonstrates parallel reduction in vascular density (77%) and reduction in nerve fiber frequency (62%) within the HO site. Conclusions: These findings represent the first work characterizing the coordination between neurogenic and angiogenic transcription programs following extremity trauma. We demonstrate through NextGen sequencing, evidence of neuroangiogenic crosstalk following musculoskeletal/neural injury. This VEGFA/NGF axis involves vascular signaling as a potential source for additional proliferation of NGF expressing pericyte/SMCs. The presented data describe the potential nerve-driven regulation contributing to the formation of HO at the extremity that with antagonism or inhibition may lead to better treatments for aberrant extremity wound healing.

Purpose: Cells recognize mechanical cues from the extracellular environment through interactions with matrix proteins, such as collagen. Following injury, fibrotic deposition of collagen can lead to aberrant cell differentiation and failed healing. Aligned collagen matrices can drive PDGFRα+ mesenchymal progenitor cells (MPCs) towards osteochondral lineages, leading to heterotopic ossification (HO). Previous work has shown that reducing mechanical strain by immobilizing a limb prevents the formation of an aligned extracellular matrix (ECM), leading to altered MPC differentiation, however, the cellular mechanisms of matrix reorganization following injury remain unclear. Using novel bioinformatics approach, we identified discoidin domain receptor 2 (DDR2) as a key MPC specific tyrosine kinase receptor that interacts with the fibrillar collagen matrix. We hypothesized that DDR2 activation leads to regulation of ECM alignment and therefore serves as a novel upstream regulator of mechanotransductive signaling following musculoskeletal repair. Methods: Heterotopic ossification was induced using a proven mouse model of 30% total body surface area burn with concurrent Achilles’ transection in Ddr2 deletion (Ddr2slie/slie) and littermate control mice on the C57/BL6J background. In separate experiments, ankle joint immobilizers were placed on injured mice for 1, 2 or 3 weeks after burn/tenotomy. Tissue from Ddr2 deleted, immobilized and mobile control mice were harvested for immunofluorescence histology, second harmonic generation of collagen fiber histology at 1, 3 and 9 weeks after injury (SHG) (n=4/group). HO site tissue was also harvested prior to injury and at 1 and 6 weeks after burn/tenotomy and processed for Single-Cell RNA sequencing (scRNA seq) and single nucleus assay for transposase-accessible chromatin (snATAC) using 10X Sequencing and downstream analysis using Seurat 4.0.1 and Signac 3.1.5. Results: Single-cell RNA sequencing showed that genes for collagen type 1 and 3 and Ddr2 are highly upregulated in MPCs following injury. SnATAC showed increased open chromatin reads in the promoter of MPCs following injury (not shown). Utilizing SHG, we found that the collagen matrix is aligned at three-weeks following injury, but one week of limb immobilization was enough to prevent aligned collagen. The active phosphorylated form of DDR2 (pDDR2) was decreased in PDGFRα+ MPCs within immobilized samples, suggesting that DDR2 may affect matrix alignment. Ddr2slie/slie had more disorganized collagen matrix nine weeks following injury and significantly reduced HO. Conclusions: This is the first work to alter collagen matrix organization by genetic modification and mobilization protocols and identifies DDR2 as a critical upstream receptor in matrix organization and aberrant progenitor differentiation following injury. DDR2 antagonism could have therapeutic potential in preventing heterotopic ossification following traumatic injury.

Purpose: Repair of distal phalanx amputation is widely studied and thought to occur through a regenerative process. Single-cell RNA sequencing (scRNA) has greatly improved the ability to characterize the cells that are involved in regeneration and abnormal healing of bone and soft tissue. Given the disorganized architecture of digit tip “regenerated” bone and its common progenitor cell to the pathologic process of heterotopic ossification, we hypothesized that digit tip repair after injury follows a program of aberrant wound repair rather than true regeneration of normal bone tissue. Methods: ScRNA data of mouse digit tip amputation (DTA) and embryonic limb development (EMB) was downloaded from NBCI GEO data base ascension number GSE135985. Additionally, scRNA data from heterotopic ossification (HO) was downloaded from GSE126060. HO, DTA, and EMB datasets were clustered individually. HO was merged and aligned with EMB and DT in separate analyses. Cells expressing the mesenchymal progenitor cell (MPC) marker Pdgfra, which we have shown to differentiate into HO and others have shown to differentiate into bone after DTA, were identified and analyzed in the HO-DTA and HO-EMB datasets. Monocle 2, Seurat 3.1.1, and Pearson correlation analysis were used for analysis and visualization. Immunostaining for markers present in DTA (ACAN, FBN-2, LTBP2) was performed on sections collected from a murine model of traumatic HO in Pdgfra-CreER;TdTomato mice induced with tamoxifen one-week prior to HO-forming injury. Results: MPC clusters from DTA and HO and from EMB and HO were aligned and projected using UMAP to compare transcription profiles. Across the timepoints, MPCs in the DTA and HO occupy similar regions of the UMAP plot, while MPCs in EMB and HO occupy largely independent regions, with only overlap at the latest time points. Using Monocle 2, cells were placed on a virtual timeline based on similarities in transcription. MPCs from DTA and HO meet at the same location on the trajectory following injury. In the EMB to HO comparison, cells only occupy similar regions of the trajectory at post-natal day 3 suggesting that bone is formed by different pathways. To understand correlations between time points, transcriptomes were also compared by Pearson analysis. MPCs following HO and DTA injuries occupy similar regions of the plot while MPCs in EMB and HO only occupy similar regions of the correlation plot at P3. Markers previously identified to be upregulated in MPCs in DTA were also upregulated in MPCs in HO by both scRNA and immunofluorescent histology. Conclusions: Cells responsible for bone repair following DTA show similar transcriptional profiles as MPCs in traumatic HO and dissimilar to MPCs in EMB. Furthermore, MPCs in both digit tip repair and HO follow trajectories that do not overlap with embryonic limb development. Thus, we demonstrate for the first time, that the process following DTA is not truly regeneration and follows programs of aberrant repair as seen in HO.