Mechanisms of bone development and repair.

Bone development occurs through a series of synchronous events that result in the formation of the body scaffold. The repair potential of bone and its surrounding microenvironment - including inflammatory, endothelial and Schwann cells - persists throughout adulthood, enabling restoration of tissue to its homeostatic functional state. The isolation of a single skeletal stem cell population through cell surface markers and the development of single-cell technologies are enabling precise elucidation of cellular activity and fate during bone repair by providing key insights into the mechanisms that maintain and regenerate bone during homeostasis and repair. Increased understanding of bone development, as well as normal and aberrant bone repair, has important therapeutic implications for the treatment of bone disease and ageing-related degeneration.

Elucidating the Mechanism of Radiation Therapy on Mesenchymal Cell Fate in Preventing Heterotopic Ossification.

Radiation therapy is a clinically proven, localized preventive measure for heterotopic ossification (HO). Despite its efficacy, there is a lack of standardization of radiation prescription dosing and fractionation, and the mechanism of the impact of radiation in HO prevention remains unknown. Here, using an established mouse model of traumatic HO induced by burn and tenotomy, we demonstrate that 7Gy in one fraction delivered to the injury site within 72 hours postoperatively significantly decreases HO formation and improves hindlimb range of motion. In-depth single-cell transcriptomic analyses, in combination with immunofluorescent staining, demonstrate decreased cellular numbers as well as aberrant endochondral differentiation and downregulation of associated upstream signaling pathways in irradiated mesenchymal progenitor cells. Our study provides the framework for future mechanistic and clinically relevant studies exploring radiation efficacy in preventing HO formation.

In vivo screening identifies SPP2, a secreted factor that negatively regulates liver regeneration.

BACKGROUND AND AIMS: The liver is remarkably regenerative and can completely recover even when 80% of its mass is surgically removed. Identification of secreted factors that regulate liver growth would help us understand how organ size and regeneration are controlled but also provide candidate targets to promote regeneration or impair cancer growth. APPROACH AND RESULTS: To enrich for secreted factors that regulate growth control, we induced massive liver overgrowth with either YAP or MYC . Differentially expressed secreted factors were identified in these livers using transcriptomic analysis. To rank candidates by functionality, we performed in vivo CRISPR screening using the Fah knockout model of tyrosinemia. We identified secreted phosphoprotein-2 (SPP2) as a secreted factor that negatively regulates regeneration. Spp2 -deficient mice showed increased survival after acetaminophen poisoning and reduced fibrosis after repeated carbon tetrachloride injections. We examined the impact of SPP2 on bone morphogenetic protein signaling in liver cells and found that SPP2 antagonized bone morphogenetic protein signaling in vitro and in vivo. We also identified cell-surface receptors that interact with SPP2 using a proximity biotinylation assay coupled with mass spectrometry. We showed that SPP2's interactions with integrin family members are in part responsible for some of the regeneration phenotypes. CONCLUSIONS: Using an in vivo CRISPR screening system, we identified SPP2 as a secreted factor that negatively regulates liver regeneration. This study provides ways to identify, validate, and characterize secreted factors in vivo.

Assessing a Structured Mental Fitness Program for Academic Acute Care Surgeons: A Pilot Study.

INTRODUCTION: There is a well-established positive correlation between improved physician wellness and patient care outcomes. Mental fitness is a component of wellness that is understudied in academic medicine. We piloted a structured mental fitness Positive Intelligence (PQ) training program for academic surgeons, hypothesizing this would be associated with improvements in PQ scores, wellness, sleep, and trainee evaluations. METHODS: This is a single-institution, prospective, mixed-methods pilot study. All active Burn/Trauma/Acute & Critical Care Surgical faculty and fellows in our division were offered the PQ program and the option to participate in this research study. The 6-wk program consists of daily exercises on a smartphone application, weekly readings, and small-group meetings with a trained mindfulness coach. Study outcomes included changes in pretraining versus post-training PQ scores, sleep hygiene, wellness, and teaching scores. A Net Promoter Score was calculated to measure user overall experience (range -100 to 100; positive scores being supportive). For secondary analysis, participants were stratified into high versus low user groups by "muscle" scores, which were calculated by program use over time. A postintervention focus group was also held to evaluate perceptions of wellness and experience with the PQ program. RESULTS: Data were analyzed for 15 participants who provided consent. The participants were primarily White (73.3%), Assistant Professors (66.7%) with Surgical Critical Care fellowship training (86.7%), and a slight female predominance (53.3%). Comparison of scores pretraining versus post-training demonstrated statistically significant increases in PQ (59 versus 65, P = 0.004), but no significant differences for sleep (24.0 versus 29.0, P = 0.33) or well-being (89.0 versus 94.0, P = 0.10). Additionally, there was no significant difference in teaching evaluations for both residents (9.1 versus 9.3, P = 0.33) and medical students (8.3 versus 8.5, P = 0.77). High versus low user groups were defined by the median muscle score (166 [Interquartile range 95.5-298.5]). High users demonstrated a statistically higher proportion of ongoing usage (75% versus 14%, P < 0.05). The final Net Promoter Score score was 25, which demonstrates program support within this group. Focus group content analysis established eight major categories: current approaches to wellness, preknowledge, reasons for participation, expected gains, program strengths, suggestions for improvement, recommendations for approaches, and sustainability. CONCLUSIONS: Our pilot study highlighted certain benefits of a structured mental fitness program for academic acute care surgeons. Our mixed-methods data demonstrate significant improvement in PQ scores, ongoing usage in high user participants, as well as interpersonal benefits such as improved connectedness and creation of a shared language within participants. Future work should evaluate this program on a higher-powered scale, with a focus on intentionality in wellness efforts, increased exposure to mental fitness, and recruitment of trainees and other health-care providers, as well as identifying the potential implications for patient outcomes.

Seraph 100 Microbind Affinity Blood Filter Does Not Clear Antibiotics: An Analysis of Antibiotic Concentration Data from PURIFY-OBS.

INTRODUCTION: Novel hemoperfusion systems are emerging for the treatment of sepsis. These devices can directly remove pathogens, pathogen-associated molecular patterns, cytokines, and other inflammatory markers from circulation. However, significant safety concerns such as potential antibiotic clearance need to be addressed prior to these devices being used in large clinical studies. METHODS: Prospective, observational study of 34 participants undergoing treatment with the Seraph 100® Microbind Affinity Blood Filter (Seraph 100) device at 6 participating sites in the USA. Patients were included for analysis if they had a record of receiving an antibiotic concurrent with Seraph 100 treatment. Patients were excluded if there was missing information for blood flow rate. Blood samples were drawn pre- and post-filter at 1 h and 4 h after treatment initiation. These average pre- and post-filter time-concentration observations were then used to estimate antibiotic clearance in L/h (CLSeraph) due to the Seraph 100 device. RESULTS: Of the 34 participants in the study, 17 met inclusion and exclusion criteria for the antibiotic analysis. Data were obtained for 7 antibiotics (azithromycin, cefazolin, cefepime, ceftriaxone, linezolid, piperacillin, and vancomycin) and one beta-lactamase inhibitor. Mean CLSeraph for the antibiotics investigated ranged from -0.57 to 0.47 L/h. No antibiotic had a CLSeraph statistically significant from 0. DISCUSSION/CONCLUSION: The Seraph 100 did not significantly clear any measured antibiotic in clinical samples. These data give further evidence to suggest that these therapies may be safely administered to critically ill patients and will not impact concentrations of administered antibiotics.

Proteome-wide abundance profiling of yeast deletion strains for GET pathway members using sample multiplexing.

The GET pathway is associated with post-translational delivery of tail-anchored (TA) proteins to the endoplasmic reticulum (ER) in yeast, as well as other eukaryotes. Moreover, dysfunction of the GET pathway has been associated with various pathological conditions (i.e., neurodegenerative disorders, cardiovascular ailments, and protein misfolding diseases). In this study, we used yeast deletion strains of Get complex members (specifically, Get1, Get2, Get3, Get4, and Get5) coupled with sample multiplexing-based quantitative mass spectrometry to profile protein abundance on a proteome-wide scale across the five individual deletion strains. Our dataset consists of over 4500 proteins, which corresponds to >75% of the yeast proteome. The data reveal several dozen proteins that are differentially abundant in one or more deletion strains, some of which are membrane-associated, yet the abundance of many TA proteins remained unchanged. This study provides valuable insights into the roles of these Get genes, and the potential for alternative pathways which help maintain cellular function despite the disruption of the GET pathway.

Macrophage-mediated PDGF Activation Correlates With Regenerative Outcomes Following Musculoskeletal Trauma.

OBJECTIVE: Our objective was to identify macrophage subpopulations and gene signatures associated with regenerative or fibrotic healing across different musculoskeletal injury types. BACKGROUND: Subpopulations of macrophages are hypothesized to fine tune the immune response after damage, promoting either normal regenerative, or aberrant fibrotic healing. METHODS: Mouse single-cell RNA sequencing data before and after injury were assembled from models of musculoskeletal injury, including regenerative and fibrotic mouse volumetric muscle loss (VML), regenerative digit tip amputation, and fibrotic heterotopic ossification. R packages Harmony , MacSpectrum , and Seurat were used for data integration, analysis, and visualizations. RESULTS: There was a substantial overlap between macrophages from the regenerative VML (2 mm injury) and regenerative bone models, as well as a separate overlap between the fibrotic VML (3 mm injury) and fibrotic bone (heterotopic ossification) models. We identified 2 fibrotic-like (FL 1 and FL 2) along with 3 regenerative-like (RL 1, RL 2, and RL 3) subpopulations of macrophages, each of which was transcriptionally distinct. We found that regenerative and fibrotic conditions had similar compositions of proinflammatory and anti-inflammatory macrophages, suggesting that macrophage polarization state did not correlate with healing outcomes. Receptor/ligand analysis of macrophage-to-mesenchymal progenitor cell crosstalk showed enhanced transforming growth factor ß in fibrotic conditions and enhanced platelet-derived growth factor signaling in regenerative conditions. CONCLUSION: Characterization of macrophage subtypes could be used to predict fibrotic responses following injury and provide a therapeutic target to tune the healing microenvironment towards more regenerative conditions.

Neutrophil and NETosis Modulation in Traumatic Heterotopic Ossification.

OBJECTIVE: To characterize the role of neutrophil extracellular traps (NETs) in heterotopic ossification (HO) formation and progression and to use mechanical and pharmacological methods to decrease NETosis and mitigate HO formation. BACKGROUND: Traumatic HO is the aberrant osteochondral differentiation of mesenchymal progenitor cells after traumatic injury, burns, or surgery. While the innate immune response has been shown to be necessary for HO formation, the specific immune cell phenotype and function remain unknown. Neutrophils, one of the earliest immune cells to respond after HO-inducing injuries, can extrude DNA, forming highly inflammatory NETs. We hypothesized that neutrophils and NETs would be diagnostic biomarkers and therapeutic targets for the detection and mitigation of HO. METHODS: C57BL6J mice underwent burn/tenotomy (a well-established mouse model of HO) or a non-HO-forming sham injury. These mice were either (1) ambulated ad libitum, (2) ambulated ad libitum with daily intraperitoneal hydroxychloroquine, ODN-2088 (both known to affect NETosis pathways), or control injections, or (3) had the injured hind limb immobilized. Single-cell analysis was performed to analyze neutrophils, NETosis, and downstream signaling after the HO-forming injury. Immunofluorescence microscopy was used to visualize NETosis at the HO site and neutrophils were identified using flow cytometry. Serum and cell lysates from HO sites were analyzed using enzyme-linked immunosorbent assay for myeloperoxidase-DNA and ELA2-DNA complexes to identify NETosis. Micro-computerized tomography was performed on all groups to analyze the HO volume. RESULTS: Molecular and transcriptional analyses revealed the presence of NETs within the HO injury site, which peaked in the early phases after injury. These NETs were highly restricted to the HO site, with gene signatures derived from both in vitro NET induction and clinical neutrophil characterizations showing a high degree of NET "priming" at the site of injury, but not in neutrophils in the blood or bone marrow. Cell-cell communication analyses revealed that this localized NET formation coincided with high levels of toll-like receptor signaling specific to neutrophils at the injury site. Reducing the overall neutrophil abundance within the injury site, either pharmacologically through treatment with hydroxychloroquine, the toll-like receptor 9 inhibitor OPN-2088, or mechanical treatment with limb offloading, results in the mitigation of HO formation. CONCLUSIONS: These data provide a further understanding of the ability of neutrophils to form NETs at the injury site, clarify the role of neutrophils in HO, and identify potential diagnostic and therapeutic targets for HO mitigation.

Tuning Macrophage Phenotype to Mitigate Skeletal Muscle Fibrosis.

Myeloid cells are critical to the development of fibrosis following muscle injury; however, the mechanism of their role in fibrosis formation remains unclear. In this study, we demonstrate that myeloid cell-derived TGF-ß1 signaling is increased in a profibrotic ischemia reperfusion and cardiotoxin muscle injury model. We found that myeloid-specific deletion of Tgfb1 abrogates the fibrotic response in this injury model and reduces fibro/adipogenic progenitor cell proliferation while simultaneously enhancing muscle regeneration, which is abrogated by adaptive transfer of normal macrophages. Similarly, a murine TGFBRII-Fc ligand trap administered after injury significantly reduced muscle fibrosis and improved muscle regeneration. This study ultimately demonstrates that infiltrating myeloid cell TGF-ß1 is responsible for the development of traumatic muscle fibrosis, and its blockade offers a promising therapeutic target for preventing muscle fibrosis after ischemic injury.

Integrating Validity Evidence to Revise a Child Abuse Knowledge Test for Early Childhood Education Providers: A Mixed Methods Approach.

Knowledge tests used to evaluate child protection training program effectiveness for early childhood education providers may suffer from threats to construct validity given the contextual variability inherent within state-specific regulations around mandated reporting requirements. Unfortunately, guidance on instrument revision that accounts for such state-specific mandated reporting requirements is lacking across research on evaluation practices. This study, therefore, explored how collection and integration of validity evidence using a mixed methods framework can guide the instrument revision process to arrive at a more valid program outcome measure.

Osteoinductive effect of soluble transforming growth factor beta receptor 3 on human osteoblast lineage.

The development of bone requires carefully choregraphed signaling to bone progenitors to form bone. Our group recently described the requirement of transforming growth factor beta receptor 3 (TGFßR3), a receptor involved in TGFß pathway signaling, during osteoblast lineage commitment in mice. The TGFß pathway is known to play multiple osteo-inductive and osteo-inhibitory roles during osteoblast development and TGFßR3 human mutations are associated with reduced bone mineral density, making TGFßR3 a unique target for bone inductive therapy. In this article, we demonstrated increased mineralization of human pediatric bone-derived osteoblast-like cells (HBO) when treated with soluble TGFßR3 (sR3) using Alizarin Red staining. Osteogenic commitment of HBO cells was demonstrated by induction of osteogenic genes RUNX2, osteocalcin, osteopontin, and osterix. Evaluation of the canonical TGFß pathway signaling demonstrated that sR3 was able to induce bone formation in HBO cells, mainly through activation of noncanonical targets of TGFß pathway signaling including AKT, ERK, and p38 MAP kinases. Inhibition of these osteogenic noncanonical pathways in the HBO cells also inhibited mineralization, suggesting they are each required. Although no induction of SMAD1, 5, and 9 was observed, there was the activation of SMAD2 and 3 suggesting that sR3 is primarily signaling via the noncanonical pathways during osteogenic induction of the HBO. Our results highlight the important role of TGFßR3 in osteoblast induction of mineralization in human bone cells through noncanonical targets of TGFß signaling. Future studies will focus on the ability of sR3 to induce bone regeneration in vivo using animal models.

Perivascular Fibro-Adipogenic Progenitor Tracing during Post-Traumatic Osteoarthritis.

Perivascular mural cells surround capillaries and microvessels and have diverse regenerative or fibrotic functions after tissue injury. Subsynovial fibrosis is a well-known pathologic feature of osteoarthritis, yet transgenic animals for use in visualizing perivascular cell contribution to fibrosis during arthritic changes have not been developed. Here, inducible Pdgfra-CreERT2 reporter mice were subjected to joint-destabilization surgery to induce arthritic changes, and cell lineage was traced over an 8-week period with a focus on the joint-associated fat pad. Results showed that, at baseline, inducible Pdgfra reporter activity highlighted adventitial and, to a lesser extent, pericytic cells within the infrapatellar fat pad. Joint-destabilization surgery was associated with marked fibrosis of the infrapatellar fat pad, accompanied by an expansion of perivascular Pdgfra-expressing cellular descendants, many of which adopted α-smooth muscle actin expression. Gene expression analysis of microdissected infrapatellar fat pad confirmed enrichment in membrane-bound green fluorescent protein/Pdgfra-expressing cells, along with a gene signature that corresponded with injury-associated fibro-adipogenic progenitors. Our results highlight dynamic changes in joint-associated perivascular fibro-adipogenic progenitors during osteoarthritis.

Low Skepticism and Positive Attitudes About Advance Care Planning Among African Americans: a National, Mixed Methods Cohort Study.

BACKGROUND: African Americans have low engagement in advance care planning (ACP). This has been attributed to healthcare distrust and skepticism about ACP. A better understanding of these attitudes is needed to address health disparities related to end-of-life care. OBJECTIVE: To explore the ACP-related values and beliefs of diverse African American communities across the USA and then the perceived value of an inexpensive end-of-life conversational game. DESIGN: Prospective, convergent, mixed methods cohort study involving fifteen underserved, African American communities across the USA. PARTICIPANTS: Of the 428 who attended events at purposively sampled sites, 90% consented to the research; 37% participated in one of 15 focus groups (n = 141). INTERVENTION: An end-of-life conversation game, played in groups of 4-6. MAIN MEASURES: The validated, 7-item ACP values and beliefs questionnaire (scaled 7 = least skeptical, 49 = most skeptical) was administered pre-game. Post-game focus groups explored perceptions about ACP and the intervention. KEY RESULTS: Participants had positive attitudes (low skepticism) about ACP with a median score of 12.00 (7.00, 20.00). Values and beliefs did not significantly differ by geographical region; however, rural areas were observed to be slightly more skeptical than urban areas (median score 14.00 vs. 11.00, p = 0.002). Themes from focus groups converged with survey data showing participants valued the ACP process and consider further engagement in ACP to be worthwhile. Subthemes emphasized the need for and value of ACP. CONCLUSIONS: Skepticism about ACP may contribute to low rates of ACP engagement in underserved African American communities. The positive attitudes uncovered in our study either negate previous findings or suggest reduced skepticism. TRIAL REGISTRATION: This study has been registered at clinicaltrials.gov ( NCT03456921 ).

The role of neutrophil extracellular traps and TLR signaling in skeletal muscle ischemia reperfusion injury.

Ischemia reperfusion (IR) injury results in devastating skeletal muscle fibrosis. Here, we recapitulate this injury with a mouse model of hindlimb IR injury which leads to skeletal muscle fibrosis. Injury resulted in extensive immune infiltration with robust neutrophil extracellular trap (NET) formation in the skeletal muscle, however, direct targeting of NETs via the peptidylarginine deiminase 4 (PAD4) mechanism was insufficient to reduce muscle fibrosis. Circulating levels of IL-10 and TNFα were significantly elevated post injury, indicating toll-like receptor (TLR) signaling may be involved in muscle injury. Administration of hydroxychloroquine (HCQ), a small molecule inhibitor of TLR7/8/9, following injury reduced NET formation, IL-10, and TNFα levels and ultimately mitigated muscle fibrosis and improved myofiber regeneration following IR injury. HCQ treatment decreased fibroadipogenic progenitor cell proliferation and partially inhibited ERK1/2 phosphorylation in the injured tissue, suggesting it may act through a combination of TLR7/8/9 and ERK signaling mechanisms. We demonstrate that treatment with FDA-approved HCQ leads to decreased muscle fibrosis and increased myofiber regeneration following IR injury, suggesting short-term HCQ treatment may be a viable treatment to prevent muscle fibrosis in ischemia reperfusion and traumatic extremity injury.

Teamwork at the Bench: Strategies for Collaborative Surgical Science in a Pandemic.

The Center for Basic and Translational Science was formed to address the unique challenges faced by surgeon-scientists. Shortly after its inception, COVID-19 upended research workflows at our institution. We discuss how the collaborative Center for Basic and Translational Science framework was adapted to support laboratories during the pandemic by assisting with ramp-down, promoting mentorship and community building, and maintaining research productivity.

Coordinating Tissue Regeneration Through Transforming Growth Factor-ß Activated Kinase 1 Inactivation and Reactivation.

Aberrant wound healing presents as inappropriate or insufficient tissue formation. Using a model of musculoskeletal injury, we demonstrate that loss of transforming growth factor-ß activated kinase 1 (TAK1) signaling reduces inappropriate tissue formation (heterotopic ossification) through reduced cellular differentiation. Upon identifying increased proliferation with loss of TAK1 signaling, we considered a regenerative approach to address insufficient tissue production through coordinated inactivation of TAK1 to promote cellular proliferation, followed by reactivation to elicit differentiation and extracellular matrix production. Although the current regenerative medicine paradigm is centered on the effects of drug treatment ("drug on"), the impact of drug withdrawal ("drug off") implicit in these regimens is unknown. Because current TAK1 inhibitors are unable to phenocopy genetic Tak1 loss, we introduce the dual-inducible COmbinational Sequential Inversion ENgineering (COSIEN) mouse model. The COSIEN mouse model, which allows us to study the response to targeted drug treatment ("drug on") and subsequent withdrawal ("drug off") through genetic modification, was used here to inactivate and reactivate Tak1 with the purpose of augmenting tissue regeneration in a calvarial defect model. Our study reveals the importance of both the "drug on" (Cre-mediated inactivation) and "drug off" (Flp-mediated reactivation) states during regenerative therapy using a mouse model with broad utility to study targeted therapies for disease. Stem Cells 2019;37:766-778.

Short-wave infrared light imaging measures tissue moisture and distinguishes superficial from deep burns.

Existing clinical approaches and tools to measure burn tissue destruction are limited resulting in misdiagnosis of injury depth in over 40% of cases. Thus, our objective in this study was to characterize the ability of short-wave infrared (SWIR) imaging to detect moisture levels as a surrogate for tissue viability with resolution to differentiate between burns of various depths. To accomplish our aim, we constructed an imaging system consisting of a broad-band Tungsten light source; 1,200-, 1,650-, 1,940-, and 2,250-nm wavelength filters; and a specialized SWIR camera. We initially used agar slabs to provide a baseline spectrum for SWIR light imaging and demonstrated the differential absorbance at the multiple wavelengths, with 1,940 nm being the highest absorbed wavelength. These spectral bands were then demonstrated to detect levels of moisture in inorganic and in vivo mice models. The multiwavelength SWIR imaging approach was used to diagnose depth of burns using an in vivo porcine burn model. Healthy and injured skin regions were imaged 72 hours after short (20 seconds) and long (60 seconds) burn application, and biopsies were extracted from those regions for histologic analysis. Burn depth analysis based on collagen coagulation histology confirmed the formation of superficial and deep burns. SWIR multispectral reflectance imaging showed enhanced intensity levels in long burned regions, which correlated with histology and distinguished between superficial and deep burns. This SWIR imaging method represents a novel, real-time method to objectively distinguishing superficial from deep burns.

Characterizing the Circulating Cell Populations in Traumatic Heterotopic Ossification.

Heterotopic ossification (HO) occurs secondary to trauma, causing pain and functional limitations. Identification of the cells that contribute to HO is critical to the development of therapies. Given that innate immune cells and mesenchymal stem cells are known contributors to HO, we sought to define the contribution of these populations to HO and to identify what, if any, contribution circulating populations have to HO. A shared circulation was obtained using a parabiosis model, established between an enhanced green fluorescent protein-positive/luciferase+ donor and a same-strain nonreporter recipient mouse. The nonreporter mouse received Achilles tendon transection and dorsal burn injury to induce HO formation. Bioluminescence imaging and immunostaining were performed to define the circulatory contribution of immune and mesenchymal cell populations. Histologic analysis showed circulating cells present throughout each stage of the developing HO anlagen. Circulating cells were present at the injury site during the inflammatory phase and proliferative period, with diminished contribution in mature HO. Immunostaining demonstrated that most early circulatory cells were from the innate immune system; only a small population of mesenchymal cells were present in the HO. We demonstrate the time course of the participation of circulatory cells in trauma-induced HO and identify populations of circulating cells present in different stages of HO. These findings further elucidate the relative contribution of local and systemic cell populations to HO.

Computed Tomography Evidence of Psoas Muscle Atrophy Without Concomitant Tendon Wasting in Early Sepsis.

BACKGROUND: Morphomic studies have demonstrated a correlation between sarcopenia and clinical outcomes in septic patients. However, tendon morphomics has not yet been studied in this context. The purpose of the present study was to evaluate tendon morphology in septic patients through analytic morphomics. We hypothesized that morphomic analyses would reveal concomitant muscle and tendon wasting in sepsis patients. The results of this study may help to implement different rehabilitation modalities for critically ill patients. MATERIALS AND METHODS: The volume and fat content of bilateral psoas muscles and tendons were measured on abdominal computed tomography scans of 25 ICU septic and 25 control trauma patients admitted to the University of Michigan between 2011 and 2012. Univariate and multivariate analyses were performed to determine the relationship between psoas muscle and tendon morphometric data, and the association with clinical variables such as smoking and comorbidities. RESULTS: Average psoas muscle volume was 12.21 ± 5.6 cm3 for control patients and 9.318 ± 3.3 cm3 in septic patients (P = 0.0023). The average psoas muscle/fat ratio for septic patients was 0.0288 ± 0.071 cm3, compared with 0.0107 ± 0.008 cm3 in the control group (P = 0.075). Average tendon volume in the septic population (0.508 ± 0.191 cm3) was not different than the control cohort (0.493 ± 0.182 cm3) (P = 0.692). CONCLUSIONS: Our results demonstrate significantly smaller psoas muscle volume in septic patients than in age-, gender-, and BMI-matched trauma patients but no demonstrable change in tendon morphology between patient groups. These findings begin to define the boundaries of clinical application within the field of morphomics.

Inhibition of Hif1α prevents both trauma-induced and genetic heterotopic ossification.

Pathologic extraskeletal bone formation, or heterotopic ossification (HO), occurs following mechanical trauma, burns, orthopedic operations, and in patients with hyperactivating mutations of the type I bone morphogenetic protein receptor ACVR1 (Activin type 1 receptor). Extraskeletal bone forms through an endochondral process with a cartilage intermediary prompting the hypothesis that hypoxic signaling present during cartilage formation drives HO development and that HO precursor cells derive from a mesenchymal lineage as defined by Paired related homeobox 1 (Prx). Here we demonstrate that Hypoxia inducible factor-1α (Hif1α), a key mediator of cellular adaptation to hypoxia, is highly expressed and active in three separate mouse models: trauma-induced, genetic, and a hybrid model of genetic and trauma-induced HO. In each of these models, Hif1α expression coincides with the expression of master transcription factor of cartilage, Sox9 [(sex determining region Y)-box 9]. Pharmacologic inhibition of Hif1α using PX-478 or rapamycin significantly decreased or inhibited extraskeletal bone formation. Importantly, de novo soft-tissue HO was eliminated or significantly diminished in treated mice. Lineage-tracing mice demonstrate that cells forming HO belong to the Prx lineage. Burn/tenotomy performed in lineage-specific Hif1α knockout mice (Prx-Cre/Hif1α(fl:fl)) resulted in substantially decreased HO, and again lack of de novo soft-tissue HO. Genetic loss of Hif1α in mesenchymal cells marked by Prx-cre prevents the formation of the mesenchymal condensations as shown by routine histology and immunostaining for Sox9 and PDGFRα. Pharmacologic inhibition of Hif1α had a similar effect on mesenchymal condensation development. Our findings indicate that Hif1α represents a promising target to prevent and treat pathologic extraskeletal bone.