Demographics and Comorbidities of United States Service Members with Combat-Related Lower Extremity Limb Salvage.

INTRODUCTION: This retrospective study describes the demographics and injury characteristics of a recently identified cohort of US Service members with combat-related lower extremity limb salvage (LS). METHODS: US Service members with combat trauma were identified from the Expeditionary Medical Encounter Database and Military Health System Data Repository and stratified into primary amputation (PA), LS, and non-threatened limb trauma (NTLT) cohorts based on ICD-9 codes. Disparities in demographic factors and injury characteristics were investigated across cohorts and within the LS cohort based on limb retention outcome. RESULTS: Cohort demographics varied by age but not by sex, branch, or rank. The mechanism of injury and injury characteristics were found to be different between the cohorts, with the LS cohort exhibiting more blast injuries and greater injury burden than their peers with NTLT. A sub-analysis of the LS population revealed more blast injuries and fewer gunshot wounds in those that underwent secondary amputation. Neither demographic factors nor total injury burden varied with limb retention outcome, despite slight disparities in AIS distribution within the LS cohort. CONCLUSIONS: In accordance with historic dogma, the LS population presents high injury severity. Demographics and injury characteristics are largely invariant with respect to limb retention outcomes, despite secondary amputation being moderately more prevalent in LS patients with blast-induced injuries. Further study of this population is necessary to better understand the factors that impact the outcomes of LS in the Military Health System.

A Data-Driven Method to Discriminate Limb Salvage from Other Combat-Related Extremity Trauma.

INTRODUCTION: The aim of this study was to address and enhance our ability to study the clinical outcome of limb salvage (LS), a commonly referenced but ill-defined clinical care pathway, by developing a data-driven approach for the identification of LS cases using existing medical code data to identify characteristic diagnoses and procedures, and to use that information to describe a cohort of US Service members (SMs) for further study. METHODS: Diagnosis code families and inpatient procedure codes were compiled and analyzed to identify medical codes that are disparately associated with a LS surrogate population of SMs who underwent secondary amputation within a broader cohort of 3390 SMs with lower extremity trauma (AIS > 1). Subsequently, the identified codes were used to define a cohort of all SMs who underwent lower extremity LS which was compared with the opinion of a panel of military trauma surgeons. RESULTS: The data-driven approach identified a population of n = 2018 SMs who underwent LS, representing 59.5% of the combat-related lower extremity (LE) trauma population. Validation analysis revealed 70% agreement between the data-driven approach and gold standard SME panel for the test cases studied. The Kappa statistic (κ = 0.55) indicates a moderate agreement between the data-driven approach and the expert opinion of the SME panel. The sensitivity and specificity were identified as 55.6% (expert range of 51.8-66.7%) and 87% (expert range of 73.9-91.3%), respectively. CONCLUSIONS: This approach for identifying LS cases can be utilized to enable future high-throughput retrospective analyses for studying both short- and long-term outcomes of this underserved patient population.

Effects of Adjunct Antifibrotic Treatment within a Regenerative Rehabilitation Paradigm for Volumetric Muscle Loss.

The use of a rehabilitation approach that promotes regeneration has the potential to improve the efficacy of pro-regenerative therapies and maximize functional outcomes in the treatment of volumetric muscle loss (VML). An adjunct antifibrotic treatment could further enhance functional gains by reducing fibrotic scarring. This study aimed to evaluate the potential synergistic effects of losartan, an antifibrotic pharmaceutical, paired with a voluntary wheel running rehabilitation strategy to enhance a minced muscle graft (MMG) pro-regenerative therapy in a rodent model of VML. The animals were randomly assigned into four groups: (1) antifibrotic with rehabilitation, (2) antifibrotic without rehabilitation, (3) vehicle treatment with rehabilitation, and (4) vehicle treatment without rehabilitation. At 56 days, the neuromuscular function was assessed, and muscles were collected for histological and molecular analysis. Surprisingly, we found that the losartan treatment decreased muscle function in MMG-treated VML injuries by 56 days, while the voluntary wheel running elicited no effect. Histologic and molecular analysis revealed that losartan treatment did not reduce fibrosis. These findings suggest that losartan treatment as an adjunct therapy to a regenerative rehabilitation strategy negatively impacts muscular function and fails to promote myogenesis following VML injury. There still remains a clinical need to develop a regenerative rehabilitation treatment strategy for traumatic skeletal muscle injuries. Future studies should consider optimizing the timing and duration of adjunct antifibrotic treatments to maximize functional outcomes in VML injuries.

Evaluating the potential use of functional fibrosis to facilitate improved outcomes following volumetric muscle loss injury.

Volumetric muscle loss (VML) was defined as the frank loss of skeletal muscle tissue with associated chronic functional deficits. Significant effort has been dedicated to developing approaches for treating VML injuries, most of which have focused on stimulating regeneration of the affected musculature via a variety of approaches (e.g., biomaterials). VML injury induces a prolonged inflammatory response which causes fibrotic tissue deposition and is thought to inhibit de novo myofiber regeneration despite observed improvements in functional outcomes (i.e., functional fibrosis; FF). Recent approaches have sought to attenuate inflammation and/or fibrosis as a means to create a permissive environment for regenerative therapies. However, there are currently no clinically available interventions capable of facilitating full restoration of form and function following VML injury; thus, an unmet clinical need exists for a near-term interventional strategy to treat affected patients. FF could serve as an alternative approach to facilitate improved functional outcomes following VML injuries. We sought to investigate whether intentionally exploiting the concept of FF (i.e., induction of a supraphysiological fibrotic response via the delivery of a polypropylene mesh combined with TGFß) would enhance the function of the VML affected musculature. We found that FF treatment induces enhanced fibrotic tissue deposition within the VML defect as evidenced by histological and molecular analysis. FF-treated animals exhibit improved in vivo muscle function compared to untreated control animals at 8 weeks post-injury, thus substantiating the concept that FF could serve as an efficacious approach for facilitating improved functional outcomes following VML injury. STATEMENT OF SIGNIFICANCE: VML injuries result in long-term functional impairments and reduced quality of life for affected individuals, namely combat injured US Service members, and no clinical interventions can restore the form and function of the injured limb. Extensive efforts have been aimed at developing therapeutics to address this critical gap; unfortunately, most interventions facilitate only modest regeneration. Interestingly, improved muscle function has been observed in VML studies following treatment with a therapeutic, despite a lack of myogenic tissue formation; a phenomenon termed Functional Fibrosis (FF). Herein we exploited the concept of FF to enhance the function of VML affected musculature. This finding is significant in that the commercially available interventions used to induce FF can be translated into the clinic near-term, thus improving the standard of care for VML injuries.

Necroptosis in the Pathophysiology of Disease.

Over the past 15 years, elegant studies have demonstrated that in certain conditions, programed cell death resembles necrosis and depends on a unique molecular pathway with no overlap with apoptosis. This form of regulated necrosis is represented by necroptosis, in which the receptor-interacting protein kinase-3 and its substrate mixed-lineage kinase domain-like protein play a crucial role. With the development of knockout mouse models and molecular inhibitors unique to necroptotic proteins, this cell death has been found to occur in virtually all tissues and diseases evaluated. There are different immunologic consequences depending on whether cells die through apoptosis or necroptosis. Therefore, distinguishing between these two forms of cell death may be crucial during pathologic evaluations. In this review, we provide an understanding of necroptotic cell-death and highlight diseases in which necroptosis has been found to play a role. We also discuss the inhibitors of necroptosis and the ways these inhibitors have been used in preclinical models of diseases. These two discussions offer an understanding of the role of necroptosis in diseases and will foster efforts to pharmacologically target this unique yet pervasive form of programed cell death in the clinic.

Local CXCR4 Upregulation in the Injured Arterial Wall Contributes to Intimal Hyperplasia.

CXCR4 is a stem/progenitor cell surface receptor specific for the cytokine stromal cell-derived factor-1 (SDF-1α). There is evidence that bone marrow-derived CXCR4-expressing cells contribute to intimal hyperplasia (IH) by homing to the arterial subintima which is enriched with SDF-1α. We have previously found that transforming growth factor-ß (TGFß) and its signaling protein Smad3 are both upregulated following arterial injury and that TGFß/Smad3 enhances the expression of CXCR4 in vascular smooth muscle cells (SMCs). It remains unknown, however, whether locally induced CXCR4 expression in SM22 expressing vascular SMCs plays a role in neointima formation. Here, we investigated whether elevated TGFß/Smad3 signaling leads to the induction of CXCR4 expression locally in the injured arterial wall, thereby contributing to IH. We found prominent CXCR4 upregulation (mRNA, 60-fold; protein, 4-fold) in TGFß-treated, Smad3-expressing SMCs. Chromatin immunoprecipitation assays revealed a specific association of the transcription factor Smad3 with the CXCR4 promoter. TGFß/Smad3 treatment also markedly enhanced SDF-1α-induced ERK1/2 phosphorylation as well as SMC migration in a CXCR4-dependent manner. Adenoviral expression of Smad3 in balloon-injured rat carotid arteries increased local CXCR4 levels and enhanced IH, whereas SMC-specific depletion of CXCR4 in the wire-injured mouse femoral arterial wall produced a 60% reduction in IH. Our results provide the first evidence that upregulation of TGFß/Smad3 in injured arteries induces local SMC CXCR4 expression and cell migration, and consequently IH. The Smad3/CXCR4 pathway may provide a potential target for therapeutic interventions to prevent restenosis. Stem Cells 2016;34:2744-2757.

A crosstalk between TGF-ß/Smad3 and Wnt/ß-catenin pathways promotes vascular smooth muscle cell proliferation.

RATIONALE: Endovascular interventions performed for atherosclerotic lesions trigger excessive vascular smooth muscle cell (SMC) proliferation leading to intimal hyperplasia. Our previous studies show that following endovascular injury, elevated TGF-ß/Smad3 promotes SMC proliferation and intimal hyperplasia. Furthermore in cultured SMCs, elevated TGF-ß/Smad3 increases the expression of several Wnt genes. Here we investigate a crosstalk between TGF-ß/Smad3 and Wnt/ß-catenin signaling and its role in SMC proliferation. METHODS AND RESULTS: To mimic TGF-ß/Smad3 up-regulation in vivo, rat aortic SMCs were treated with Smad3-expressing adenovirus (AdSmad3) or AdGFP control followed by stimulation with TGF-ß1 (or solvent). AdSmad3/TGF-ß treatment up-regulated Wnt2b, Wnt4, Wnt5a, Wnt9a, and Wnt11 (confirmed by qRT-PCR and ELISA), and also increased ß-catenin protein as detected by Western blotting. Blocking Wnt signaling using a Frizzled receptor inhibitor (Niclosamide) abolished TGF-ß/Smad3-induced ß-catenin stabilization. Increasing ß-catenin through degradation inhibition (using SKL2001) or by adenoviral expression enhanced SMC proliferation. Furthermore, application of recombinant Wnt2b, Wnt4, Wnt5a, or Wnt9a, but not Wnt11, stabilized ß-catenin and stimulated SMC proliferation as well. In addition, increased ß-catenin was found in the neointima of injured rat carotid artery where TGF-ß and Smad3 are known to be up-regulated. CONCLUSIONS: These results suggest a novel mechanism whereby elevated TGF-ß/Smad3 stimulates the secretion of canonical Wnts which in turn enhances SMC proliferation through ß-catenin stabilization. This crosstalk between TGF-ß/Smad3 and Wnt/ß-catenin canonical pathways provides new insights into the pathophysiology of vascular SMCs linked to intimal hyperplasia.

TGF-ß/Smad3 stimulates stem cell/developmental gene expression and vascular smooth muscle cell de-differentiation.

Atherosclerotic-associated diseases are the leading cause of death in the United States. Despite recent progress, interventional treatments for atherosclerosis can be complicated by restenosis resulting from neo-intimal hyperplasia. We have previously demonstrated that TGF-ß and its downstream signaling protein Smad3 ∶ 1) are up-regulated following vascular injury, 2) together drive smooth muscle cell (SMC) proliferation and migration and 3) enhance the development of intimal hyperplasia. In order to determine a mechanism through which TGF-ß/Smad3 promote these effects, Affymetrix gene expression arrays were performed on primary rat SMCs infected with Smad3 and stimulated with TGF-ß or infected with GFP alone. More than 200 genes were differentially expressed (>2.0 fold change, p<0.05) in TGF-ß/Smad3 stimulated SMCs. We then performed GO term enrichment analysis using the DAVID bioinformatics database and found that TGF-ß/Smad3 activated the expression of multiple genes related to either development or cell differentiation, several of which have been shown to be associated with multipotent stem or progenitor cells. Quantitative real-time PCR confirmed up-regulation of several developmental genes including FGF1, NGF, and Wnt11 (by 2.5, 6 and 7 fold, respectively) as well as stem/progenitor cell associated genes CD34 and CXCR4 (by 10 and 45 fold, respectively). In addition, up-regulation of these factors at protein levels were also confirmed by Western blotting, or by immunocytochemistry (performed for CXCR4 and NGF). Finally, TGF-ß/Smad3 down regulated transcription of SMC contractile genes as well as protein production of smooth muscle alpha actin, calponin, and smooth muscle myosin heavy chain. These combined results suggest that TGF-ß/Smad3 stimulation drives SMCs to a phenotypically altered state of de-differentiation through the up-regulation of developmental related genes.