Hypoxia inducible factor 2α promotes tolerogenic macrophage development during cardiac transplantation through transcriptional regulation of colony stimulating factor 1 receptor.

Solid organ transplantation mobilizes myeloid cells, including monocytes and macrophages, which are central protagonists of allograft rejection. However, myeloid cells can also be functionally reprogrammed by perioperative costimulatory blockade to promote a state of transplantation tolerance. Transplantation tolerance holds promise to reduce complications from chronic immunosuppression and promote long-term survival in transplant recipients. We sought to identify different mediators of transplantation tolerance by performing single-cell RNA sequencing of acute rejecting or tolerized cardiac allografts. This led to the unbiased identification of the transcription factor, hypoxia inducible factor (HIF)-2α, in a subset of tolerogenic monocytes. Using flow cytometric analyses and mice with conditional loss or gain of function, we uncovered that myeloid cell expression of HIF-2α was required for costimulatory blockade-induced transplantation tolerance. While HIF-2α was dispensable for mobilization of tolerogenic monocytes, which were sourced in part from the spleen, it promoted the expression of colony stimulating factor 1 receptor (CSF1R). CSF1R mediates monocyte differentiation into tolerogenic macrophages and was found to be a direct transcriptional target of HIF-2α in splenic monocytes. Administration of the HIF stabilizer, roxadustat, within micelles to target myeloid cells, increased HIF-2α in splenic monocytes, which was associated with increased CSF1R expression and enhanced cardiac allograft survival. These data support further exploration of HIF-2α activation in myeloid cells as a therapeutic strategy for transplantation tolerance.

Altered kidney distribution and loss of ACE2 into the urine in acute kidney injury.

There are diverse pathophysiological mechanisms involved in acute kidney injury (AKI). Among them, overactivity of the renin-angiotensin system (RAS) has been described. Angiotensin-converting enzyme 2 (ACE2) is a tissue RAS enzyme expressed in the apical border of proximal tubules. Given the important role of ACE2 in the metabolism of angiotensin II, this study aimed to characterize kidney and urinary ACE2 in a mouse model of AKI. Ischemia-reperfusion injury (IRI) was induced in C57BL/6 mice by clamping of the left renal artery followed by removal of the right kidney. In kidneys harvested 48 h after IRI, immunostaining revealed a striking maldistribution of ACE2 including spillage into the tubular lumen and the presence of ACE2-positive luminal casts in the medulla. In cortical membranes, ACE2 protein and enzymatic activity were both markedly reduced (37 ± 4 vs. 100 ± 6 ACE2/ß-actin, P = 0.0004, and 96 ± 14 vs. 152 ± 6 RFU/µg protein/h, P = 0.006). In urine, full-length membrane-bound ACE2 protein (100 kDa) was markedly increased (1,120 ± 405 vs. 100 ± 46 ACE2/µg creatinine, P = 0.04), and casts stained for ACE2 were recovered in the urine sediment. In conclusion, in AKI caused by IRI, there is a marked loss of ACE2 from the apical tubular border with deposition of ACE2-positive material in the medulla and increased urinary excretion of full-length membrane-bound ACE2 protein. The deficiency of tubular ACE2 in AKI suggests that provision of this enzyme could have therapeutic applications and that its excretion in the urine may also serve as a diagnostic marker of severe proximal tubular injury.NEW & NOTEWORTHY This study provides novel insights into the distribution of kidney ACE2 in a model of AKI by IRI showing a striking detachment of apical ACE2 from proximal tubules and its loss in urine and urine sediment. The observed deficiency of kidney ACE2 protein and enzymatic activity in severe AKI suggests that administration of forms of this enzyme may mitigate AKI and that urinary ACE2 may serve as a potential biomarker for tubular injury.

Pediatric Floating Elbows What Is All the Fuss About? A Multicenter Perspective.

BACKGROUND: Classic orthopaedic teaching states a high risk of pediatric acute compartment syndrome (PACS) and other adverse outcomes to be associated with pediatric floating elbow injuries. However, more recent data suggest otherwise. This study aims to evaluate treatment approaches and outcomes of pediatric floating elbow injuries and accurately determine the rate of associated PACS. METHODS: A multicenter retrospective database was created to review patients below 18 years old who presented between 2014 and 2019 with floating elbow injuries. Patient demographics, injury characteristics, treatment course, and outcomes were evaluated. A severity classification (Children's Orthopaedic Trauma and Infection Consortium for Evidence-Based Studies) was established: class 1 injuries included Gartland 1 supracondylar fracture, class 2 included Gartland 2 supracondylar fracture, and class 3 included Gartland 3 or 4 supracondylar or t-condylar fracture. Subclasses A and B were based on displacement of the distal fracture. RESULTS: Four hundred fifty four patients were evaluated across 15 institutions. The cohort was 51% male and a median of 6.8 years old at injury. Thirteen patients (2.9%) presented without a palpable or dopplerable pulse, all having class 3 injuries. Ninety patients (20.0%) presented with nerve injuries, which were more common in class 3 injuries ( P <0.001). Only 14 (3.1%) had persistent nerve injuries at the final follow-up. Displacement largely dictated whether the distal injury was treated with fixation ( P <0.001) or immobilization only. Open reduction rate of the proximal fracture was 7.7% overall. There was 1 case (0.2%) of PACS involving displaced proximal and distal fractures. The median length of follow-up was 2.5 months. Modified Flynn outcomes at the last clinical visit were excellent/good in 315 patients (70%). More severe injuries had less good/excellent outcomes than less severe injuries ( P =0.030). CONCLUSIONS: This multicenter study of a large cohort of pediatric floating elbow injuries identified a low rate of PACS (0.2%). Closed treatment of the distal fracture was more frequently performed for nondisplaced fractures. Nerve and vascular injury rates were consistent with those of isolated component fractures and were associated with fracture displacement. The Children's Orthopaedic Trauma and Infection Consortium for Evidence-based Studies classification was an effective predictor of outcomes. LEVEL OF EVIDENCE: Level IV.

Adolescent Idiopathic Scoliosis Minimum Data Set: Towards Standardization of Data Elements in History and Physical Examination.

INTRODUCTION: Nonoperative care represents a cornerstone of adolescent idiopathic scoliosis (AIS) management, although no consensus exists for a minimal data set. We aimed to determine a consensus in critical data points to obtain during clinical AIS visits. METHODS: A REDCap-based survey was distributed to Pediatric Orthopedic Society of America (POSNA), Pediatric Spine Study Group (PSSG), and International Society on Scoliosis Orthopedic and Rehabilitation Treatment (SOSORT). Respondents ranked the importance of data points in history, physical examination, and bracing during AIS visits.  Results: One hundred eighty-one responses were received (26% response rate), of which 86% were physicians and 14% were allied health professionals. About 80% of respondents worked at pediatric hospitals or pediatric spaces within adult hospitals, and 82% were academic, with the majority (57%) seeing 150+ unique AIS patients annually. Most respondents recommended six-month follow-up for patients under observation (60%) and bracing (54%). Most respondents (75%) considered family history and pain important (69%), with the majority (69%) asking about pain at every visit. Across all time points, Adam's forward bend test, shoulder level, sagittal contour, trunk shift, and curve stiffness were all considered critically important (>60%). At the first visit, scapular prominence, leg lengths, motor and neurological examination, gait, and iliac crest height were also viewed as critical. At the preoperative visit, motor strength and scapular prominence should also be documented. About 39% of respondents use heat sensors to monitor bracing compliance, and average brace wear since the prior visit was considered the most important (85%) compliance data point. CONCLUSIONS: This study establishes recommendations for a 19-item minimum data set for clinical AIS evaluation, including history, physical exam, and bracing, to allow for future multicenter registry-based studies.

Should I stay or should I go: an assessment of criteria for safe day of surgery discharge of displaced supracondylar humerus fractures.

Immobilization type and in-hospital observation following surgical management of displaced supracondylar fractures are subject to surgeon preference and training. Our goal was to determine criteria for immediate discharge and optimal type of immobilization. Medical records of 661 patients with type III, IV or flexion-type displaced supracondylar humerus fractures treated at a level 1 pediatric trauma center from January 2013 to September 2019 were reviewed. Patients were separated into 'admission appropriate' (AA = 113) and 'discharge appropriate' (DA = 548) sub-cohorts. Neurovascular deficit at presentation (P < 0.001), post-operative physical exam deterioration (P < 0.001), age (P < 0.001) and post-operative immobilization modality (P = 0.02) were significantly different between AA and DA groups. When comparing patients who presented with neurologic deficit to those neurovascularly intact, there was a significant difference in whether circumferential immobilization was used post-operatively (P < 0.001), IV medication need (P < 0.001), discharge or admission (P < 0.001), neurologic decline (P < 0.001), return to ED (P = 0.008) and vascular compromise (P = 0.05). Twenty-four of the 56 (43%) patients who were AA and had no neurovascular finding on presentation had their immobilization adjusted (bivalved or loosened) to accommodate for swelling overnight. Only 1 was initially maintained in a splint or bivalved cast; the other 23 were initially maintained post-operatively in circumferential immobilization (P = 0.01). Our findings suggest that patients with intact neurovascular exams at presentation are candidates for early discharge, and splinting or bivalved casting may be preferable, especially in patients who are discharged.

Rotation and Asymmetry of the Axial Plane Pelvis in Cerebral Palsy: A CT-Based Study.

Spinopelvic malignment is commonly seen with non-ambulatory cerebral palsy (CP). Axial plane deformation is not well described in the literature. The purpose of this study was to describe and quantify the axial plane deformity in CP using CT scans and compare it to normal controls. We retrospectively collected data using CT scans of the abdomen and pelvis of 40 patients with GMFCS IV/V CP and neuromuscular scoliosis (CPP) and normal controls (NP) matched by age and sex. Pre-operative Cobb angle was recorded for the CP patients. Pelvic anatomy was evaluated at the supra-acetabular region of bone using two angles-iliac wing angle and sacral ala angle, measured for each hemipelvis. The larger of each hemipelvis angle was considered externally rotated while the smaller angle was considered internally rotated, termed as follows-iliac wing external (IWE) and internal (IWI); sacral ala external (SAE), and internal (SAI). Differences were noted using an independent t-test while correlations with Cobb angle were performed using Pearson's correlation. Iliac wing measurements showed the externally rotated hemipelvis showed a significantly greater magnitude compared with normal controls at 47.3 ± 18.1 degrees vs. 26.4 ± 3.7 degrees in NP (p < 0.001) while no internal rotation was observed (p > 0.05). Sacral ala measurements showed greater magnitude in both external and internal rotation. SAE was 119.5 ± 9.5 degrees in CPP vs. 111.2 ± 7.7 degrees in NP (p < 0.001) while SAI was 114.1 ± 8.5 degrees in CPP vs. 107.9 ± 7.5 degrees in NP (p = 0.001). In the CP cohort, the mean Cobb angle was 61.54 degrees (n = 37/40). Cobb angle correlated with the degree of external iliac wing rotation-IWE (r = 0.457, p = 0.004) and degree of absolute difference in the rotation of the iliac wing (r = 0.506, p = 0.001). The pelvis in a patient with CP scoliosis is asymmetrically oriented exhibiting a greater external rotation of one hemipelvis relative to normal controls. The severity of neuromuscular scoliosis is related to the pelvic axial rotation in CP patients. Axial plane deformity exists in the CP pelvis and this deformity warrants consideration when considering spinopelvic instrumentation strategies and outcomes of supra-pelvic and infra-pelvic pathologies.

Single-cell coating with biomimetic extracellular nanofiber matrices.

Cell therapies offer great promise in the treatment of diseases and tissue regeneration, but their clinical use has many challenges including survival, optimal performance in their intended function, or localization at sites where they are needed for effective outcomes. We report here on a method to coat a biodegradable matrix of biomimetic nanofibers on single cells that could have specific functions ranging from cell signaling to targeting and helping cells survive when used for therapies. The fibers are composed of peptide amphiphile (PA) molecules that self-assemble into supramolecular nanoscale filaments. The PA nanofibers were able to create a mesh-like coating for a wide range of cell lineages with nearly 100 % efficiency, without interrupting the natural cellular phenotype or functions. The targeting abilities of this system were assessed in vitro using human primary regulatory T (hTreg) cells coated with PAs displaying a vascular cell adhesion protein 1 (VCAM-1) targeting motif. This approach provides a biocompatible method for single-cell coating that does not negatively alter cellular phenotype, binding capacity, or immunosuppressive functionality, with potential utility across a broad spectrum of cell therapies. STATEMENT OF SIGNIFICANCE: Cell therapies hold great promise in the treatment of diseases and tissue regeneration, but their clinical use has been limited by cell survival, targeting, and function. We report here a method to coat single cells with a biodegradable matrix of biomimetic nanofibers composed of peptide amphiphile (PA) molecules. The nanofibers were able to coat cells, such as human primary regulatory T cells, with nearly 100 % efficiency, without interrupting the natural cellular phenotype or functions. The approach provides a biocompatible method for single-cell coating that does not negatively alter cellular phenotype, binding capacity, or immunosuppressive functionality, with potential utility across a broad spectrum of cell therapies.