Identification of the Human Skeletal Stem Cell.

Stem cell regulation and hierarchical organization of human skeletal progenitors remain largely unexplored. Here, we report the isolation of a self-renewing and multipotent human skeletal stem cell (hSSC) that generates progenitors of bone, cartilage, and stroma, but not fat. Self-renewing and multipotent hSSCs are present in fetal and adult bones and can also be derived from BMP2-treated human adipose stroma (B-HAS) and induced pluripotent stem cells (iPSCs). Gene expression analysis of individual hSSCs reveals overall similarity between hSSCs obtained from different sources and partially explains skewed differentiation toward cartilage in fetal and iPSC-derived hSSCs. hSSCs undergo local expansion in response to acute skeletal injury. In addition, hSSC-derived stroma can maintain human hematopoietic stem cells (hHSCs) in serum-free culture conditions. Finally, we combine gene expression and epigenetic data of mouse skeletal stem cells (mSSCs) and hSSCs to identify evolutionarily conserved and divergent pathways driving SSC-mediated skeletogenesis. VIDEO ABSTRACT.

Mechanoresponsive stem cells acquire neural crest fate in jaw regeneration.

During both embryonic development and adult tissue regeneration, changes in chromatin structure driven by master transcription factors lead to stimulus-responsive transcriptional programs. A thorough understanding of how stem cells in the skeleton interpret mechanical stimuli and enact regeneration would shed light on how forces are transduced to the nucleus in regenerative processes. Here we develop a genetically dissectible mouse model of mandibular distraction osteogenesis-which is a process that is used in humans to correct an undersized lower jaw that involves surgically separating the jaw bone, which elicits new bone growth in the gap. We use this model to show that regions of newly formed bone are clonally derived from stem cells that reside in the skeleton. Using chromatin and transcriptional profiling, we show that these stem-cell populations gain activity within the focal adhesion kinase (FAK) signalling pathway, and that inhibiting FAK abolishes new bone formation. Mechanotransduction via FAK in skeletal stem cells during distraction activates a gene-regulatory program and retrotransposons that are normally active in primitive neural crest cells, from which skeletal stem cells arise during development. This reversion to a developmental state underlies the robust tissue growth that facilitates stem-cell-based regeneration of adult skeletal tissue.

Combined Targeted Muscle Reinnervation With Regenerative Peripheral Nerve Interfaces Decreases Long-Term Narcotic Use in Amputees: A Case Control Study.

PURPOSE: Combined targeted muscle reinnervation with regenerative peripheral nerve interfaces ("TMRpni") is a recently described nerve management strategy that leverages beneficial elements of targeted muscle reinnervation (TMR) and regenerative peripheral nerve interface (RPNI) techniques. This study aimed to evaluate the effect of TMRpni on long-term opioid consumption after amputation. We hypothesize that TMRpni decreases chronic opioid consumption in amputees. METHODS: This is a retrospective cohort study of all patients who underwent TMRpni between 2019 and 2021. These patients were age-matched at a 1:1 ratio with a control group of patients who underwent amputation without TMRpni. Statistical analysis was performed using SPSS Version 28.0. RESULTS: Thirty-one age-matched pairs of patients in the TMRpni and control groups were included. At 30 days after surgery, there was no significant difference in number of patients who required an additional refill of their opioid prescriptions (45% vs 55%, P = 0.45) or patients who continued to actively use opioids (36% vs 42%, P = 0.60). However, at 90 days after surgery, there was a significantly lower number of patients from the TMRpni group who reported continued opioid use compared with the control group (10% vs 32%, P = 0.03). CONCLUSIONS: This study demonstrates that TMRpni may translate to decreased rates of chronic opiate use. Continued study is indicated to optimize TMRpni techniques and patient selection and to determine its long-term efficacy.

A Comparison of Perineal Myocutaneous Flaps Following Abdominoperineal Excision of the Rectum for Anorectal Pathology.

BACKGROUND: Flap-based reconstruction following abdominoperineal resection has been used to address the resultant soft tissue defect and reduce postoperative wound complications. Vertical rectus abdominis myocutaneous flaps have been the traditional choice, but locoregional flaps have attracted attention in minimally invasive resection because they avoid additional abdominal dissection. However, few data exist comparing flap types. OBJECTIVE: To compare outcomes for different types of perineal reconstruction in patients undergoing abdominoperineal resection exclusively for anorectal pathology. DESIGN: This was a retrospective comparative study. SETTING: This study was conducted at a large, tertiary referral institution. PATIENTS: Following Institutional Review Board approval, prospectively maintained clinical and financial databases were interrogated and cross-referenced for patients undergoing proctectomy or abdominoperineal resection with flap reconstruction from 2007 to 2018. Patients with primary gynecological or urological pathology were excluded. MAIN OUTCOME MEASURES: The primary outcome was flap complication rate. Secondary outcomes included perineal hernia rate, donor site complications, emergency department consult after discharge, readmission <90 days, and length of stay. Data were analyzed using univariate and multivariate techniques. RESULTS: A total of 135 patients (79 female, median age 58 years) were included: 68 rectus, 52 gluteal, and 15 gracilis flap reconstructions. Median follow-up was 46 months. Rates of both major and minor flap complications were similar for rectus and gluteal flaps, even when controlling for differences between groups via multivariate analysis ( p > 0.9), including extent of resection and use of mesh. For all flaps, American Society of Anesthesiology score ≥3 was the only independent predictor of major, but not minor, flap complications. For rectus and gluteal flaps, smoking, female sex, and American Society of Anesthesiology score ≥3 were independent predictors of major flap complications ( p < 0.05). LIMITATIONS: This study was limited by its retrospective nature and potential selection bias associated with flap choice; it was also impossible to quantify defect size. CONCLUSION: Gluteal flaps have similar complication rates to rectus flaps and may be considered for patients who are otherwise suitable for minimally invasive abdominoperineal resection. See Video Abstract at http://links.lww.com/DCR/B866 .Una comparación de los colgajos miocutáneos perineales después de la escisión abdominoperineal del recto para patología anorectal. ANTECEDENTES: La reconstrucción con colgajo después de la resección abdominoperineal se ha utilizado para abordar el defecto de tejido blando resultante y reducir las complicaciones postoperatorias de la herida. Los colgajos miocutáneos verticales del recto abdominal han sido la elección tradicional, pero los colgajos locorregionales han atraído la atención en la resección mínimamente invasiva porque evitan la disección abdominal adicional. Sin embargo, existen pocos datos que comparen los tipos de colgajos.

Wounds Inhibit Tumor Growth In Vivo.

OBJECTIVE: The aim of this study was to determine the interaction of full thickness excisional wounds and tumors in vivo. SUMMARY OF BACKGROUND DATA: Tumors have been described as wounds that do not heal due to similarities in stromal composition. On the basis of observations of slowed tumor growth after ulceration, we hypothesized that full thickness excisional wounds would inhibit tumor progression in vivo. METHODS: To determine the interaction of tumors and wounds, we developed a tumor xenograft/allograft (human head and neck squamous cell carcinoma SAS/mouse breast carcinoma 4T1) wound mouse model. We examined tumor growth with varying temporospatial placement of tumors and wounds or ischemic flap. In addition, we developed a tumor/wound parabiosis model to understand the ability of tumors and wounds to recruit circulating progenitor cells. RESULTS: Tumor growth inhibition by full thickness excisional wounds was dose-dependent, maintained by sequential wounding, and relative to distance. This effect was recapitulated by placement of an ischemic flap directly adjacent to a xenograft tumor. Using a parabiosis model, we demonstrated that a healing wound was able to recruit significantly more circulating progenitor cells than a growing tumor. Tumor inhibition by wound was unaffected by presence of an immune response in an immunocompetent model using a mammary carcinoma. Utilizing functional proteomics, we identified 100 proteins differentially expressed in tumors and wounds. CONCLUSION: Full thickness excisional wounds have the ability to inhibit tumor growth in vivo. Further research may provide an exact mechanism for this remarkable finding and new advances in wound healing and tumor biology.

Technical considerations in nonreconstructive mastectomy patients.

BACKGROUND: Not all women undergo post-mastectomy breast reconstruction due to medical comorbidities or personal preference. An aesthetically pleasing closure and contour of the chest wall is still desired, though may be technically difficult to achieve in some patients. By combining techniques and lessons learned from breast reductions and female-to-male mastectomies (FTTM), we present a technical approach to aesthetic primary closure post-mastectomy that can be utilized in patients regardless of preoperative breast size. METHODS: After mastectomy, excess cranial/caudal tissue is determined and the lower flap is de-epithelialized to allow for bulk in the reconstructed breast. Excess tissue in the horizontal plane is assessed, and axillary, nonbreast tissue is medialized. Excess skin in the horizontal plane is removed with a small lateral incision similar to a wise-pattern closure. RESULTS: We have performed this technique with good aesthetic results and satisfied patients postoperatively. CONCLUSION: When performing post-mastectomy closure without reconstruction, attention to tissue excess, medialization of axillary tissue and providing bulk with lateral and caudal tissue allows for an easy, reproducible, and aesthetic closure.

Scarless wound healing: finding the right cells and signals.

From the moment we are born, every injury to the skin has the potential to form a scar, many of which can impair form and/or function. As such, scar management constitutes a billion-dollar industry. However, effectively promoting scarless wound healing remains an elusive goal. The complex interactions of wound healing contribute to our inability to recapitulate scarless wound repair as it occurs in nature, such as in fetal skin and the oral mucosa. However, many new advances have occurred in recent years, some of which have translated scientific findings from bench to bedside. In vivo lineage tracing has helped establish a variety of novel cellular culprits that may act as key drivers of the fibrotic response. These newly characterized cell populations present further targets for therapeutic intervention, some of which have previously demonstrated promising results in animal models. Here, we discuss several recent studies that identify exciting approaches for diminishing scar formation. Particular attention will also be paid to the canonical Wnt/ß-catenin signaling pathway, which plays an important role in both embryogenesis and tissue repair. New insights into the differential effects of Wnt signaling on heterogeneous fibroblast and keratinocyte populations within the skin further demonstrate methods by which wound healing can be re-directed to a more fetal scarless phenotype. Graphical abstract Recent approaches to reducing scar formation. Representation showing novel scientific approaches for decreasing scar formation, including the targeting of pro-fibrotic cell populations based on surface molecule expression (e.g. DPP4(+) fibroblasts, ADAM12(+) pericytes). Modulation of cellular mechanotransduction pathways are another means to reduce scar formation, both at the molecular level or, macroscopically with dressings designed to offload tension, at cutaneous wound sites (ADAM12 a disintegrin and metalloprotease 12, DPP4 dipeptidyl peptidase-4, FAK focal adhesion kinase).

Preinjury Social Determinants of Health Disparities Predict Postinjury Psychosocial Conditions in Adult Traumatic Brachial Plexus Injuries.

BACKGROUND: Adult traumatic brachial plexus injuries (TBPIs) are life-altering events that can have detrimental effects on a patient's quality of life. OBJECTIVE: To examine how social determinants of health (SDOH) disparities influence the risk of developing new psychosocial conditions after TBPIs in previously psychiatric-naïve patients. METHODS: Between January 2010 and June 2019, a retrospective analysis was performed using PearlDiver's Mariner, an all-payer claims database, to create 3 cohorts: TBPI disparity cohort: patients with TBPI and presence of at least 1 SDOH disparity before injury, TBPI without disparity cohort: patients with TBPI and the absence of any SDOH disparity, and control cohort: patients without TBPIs. RESULTS: The matched population analyzed in this study consisted of 1176 patients who were equally represented in the TBPI disparity cohort (n = 392, 33.33%), TBPI without disparity cohort (n = 392, 33.33%), and control cohort (n = 392, 33.33%). A total of 301 patients developed any psychosocial condition with 4 years of their injury. Patients in the TBPI disparity cohort had significantly higher rates of developing any psychosocial condition (31.12%, P < .0005), depression (22.70%, P = .0032), anxiety (18.62%, P = .0203), drug abuse (7.91%, P = .0060), and alcohol abuse (4.85%, P = .03499) when compared with the other cohorts. Furthermore, the disparity cohort carried a significantly increased risk of developing any psychosocial condition (hazard ratio 1.42, 95% CI 1.09-1.86). The rates of suicide attempt, post-traumatic stress disorder, and divorce did not significantly differ between groups. CONCLUSION: TBPI patients with SDOH disparities are at increased risk of developing new-onset psychosocial conditions, such as depression, anxiety, drug abuse, and alcohol abuse. Level of Evidence: Prognostic Level III.

Pre-appendectomy hyponatremia is associated with increased rates of complicated appendicitis.

Background: Acute appendicitis is one of the most common surgical emergencies worldwide. Preoperative assessment of the risk of complicated appendicitis may aid in treatment planning. We sought to investigate the association between pre-appendectomy hyponatremia and diagnosis of complicated appendicitis. Methods: The TriNetX platform, a federated health research network that aggregates de-identified electronic health record data of over 90 million patients across the United States, was queried for patients who underwent appendectomy starting January 2019 and who had at least one sodium value from the preoperative period. The study population was stratified into three age groups: pediatric (age < 18), adult (age 18-64), and older adult (age ≥ 65). These groups were subdivided into patients with preoperative hyponatremia (<135 mmol/L) and normonatremia (135-145 mmol/L). Results: Among the 61,245 patients who met inclusion criteria, 17,546 were included for analysis following propensity score matching. The odds of complicated appendicitis were highest in pediatric patients (age < 18) with pre-appendectomy hyponatremia (odds ratio [OR] = 2.91, 95 % CI [2.53, 3.35]). Patients age 18-64 and aged ≥ 65 with preoperative hyponatremia also demonstrated increased odds of a complicated appendicitis diagnosis, but to a lesser extent (OR = 2.11, 95 % CI [1.92, 2.32] (OR = 1.49, 95 % CI [1.25, 1.77], respectively). Conclusions: In a large analysis of matched patients with acute appendicitis, we found an association between immediate preoperative hyponatremia and complicated appendicitis. Future studies are indicated to further evaluate the role of hyponatremia as a potential diagnostic marker for complicated appendicitis in all age groups. Key message: This study suggests a role of hyponatremia as one of multiple variables to incorporate into future clinical decision tools for complicated acute appendicitis.

Intestinal Pdx1 mediates nutrient metabolism gene networks and maternal expression is essential for perinatal growth in mice.

The homeodomain transcription factor Pdx1 is essential for pancreas formation and functions in pancreatic islets cells to regulate genes involved in maintenance of glucose homeostasis. In order to investigate a role for Pdx1 in intestinal cells, we analyzed the functions and networks associated with genes differentially expressed by Pdx1 overexpression in human Caco-2 cells. In agreement with previous results for intestine isolated from mice with Pdx1 inactivation, functional analysis of genes differentially expressed with Pdx1 overexpression revealed functions significantly associated with nutrient metabolism. Similarly, network analysis examining the interactions among the differentially expressed genes revealed gene networks involved in lipid metabolism. Consistent with defects in maternal nutrient metabolism, mouse pups born to dams with intestine-specific Pdx1 inactivation are underweight and fail to thrive in the neonatal period compared to pups born to control dams. We conclude that Pdx1 mediates lipid metabolism gene networks in intestinal cells and that maternal expression is essential for perinatal growth in mice.

Prrx1 Fibroblasts Represent a Pro-fibrotic Lineage in the Mouse Ventral Dermis.

Fibroblast heterogeneity has been shown within the unwounded mouse dorsal dermis, with fibroblast subpopulations being identified according to anatomical location and embryonic lineage. Using lineage tracing, we demonstrate that paired related homeobox 1 (Prrx1)-expressing fibroblasts are responsible for acute and chronic fibroses in the ventral dermis. Single-cell transcriptomics further corroborated the inherent fibrotic characteristics of Prrx1 fibroblasts during wound repair. In summary, we identify and characterize a fibroblast subpopulation in the mouse ventral dermis with intrinsic scar-forming potential.

Cutaneous Scarring: Basic Science, Current Treatments, and Future Directions.

Significance: Scarring of the skin from burns, surgery, and injury constitutes a major burden on the healthcare system. Patients affected by major scars, particularly children, suffer from long-term functional and psychological problems. Recent Advances: Scarring in humans is the end result of the wound healing process, which has evolved to rapidly repair injuries. Wound healing and scar formation are well described on the cellular and molecular levels, but truly effective molecular or cell-based antiscarring treatments still do not exist. Recent discoveries have clarified the role of skin stem cells and fibroblasts in the regeneration of injuries and formation of scar. Critical Issues: It will be important to show that new advances in the stem cell and fibroblast biology of scarring can be translated into therapies that prevent and reduce scarring in humans without major side effects. Future Directions: Novel therapies involving the use of purified human cells as well as agents that target specific cells and modulate the immune response to injury are currently undergoing testing. In the basic science realm, researchers continue to refine our understanding of the role that particular cell types play in the development of scar.

Noncoding RNAs in Wound Healing: A New and Vast Frontier.

Significance: Wound healing requires a highly orchestrated coordination of processes that are not yet fully understood. Therefore, available clinical therapies are thus far limited in their efficacy in preventing and treating both chronic wounds and scars. Current gene-based therapeutics is largely based on our understanding of the protein-coding genome and proteins involved in known wound healing pathways. Recent Advances: Noncoding RNAs such as microRNAs and long noncoding RNAs have recently been found to be significant modulators of gene expression in diverse cellular pathways. Research has now implicated noncoding RNAs in nearly every stage of the wound healing process, suggesting that they may serve as clinical therapeutic targets. Noncoding RNAs are critical regulators in processes such as angiogenesis and cutaneous cell migration and proliferation, including classically described biological pathways previously attributed to mostly protein constituents. Critical Issues: The complexity and diversity of the interactions of noncoding RNAs with their targets and other binding partners require thorough characterization and understanding of their functions before they may be altered to modulate human wound healing pathways. Future Directions: Research in the area of noncoding RNAs continues to rapidly expand our understanding of their potential roles in physiological and pathological wound healing. Coupled with improving technologies to enhance or suppress target noncoding RNA in vivo, these advances hold great promise in the development of new therapies for wound healing.

Mechanical Forces in Cutaneous Wound Healing: Emerging Therapies to Minimize Scar Formation.

Significance: Excessive scarring is major clinical and financial burden in the United States. Improved therapies are necessary to reduce scarring, especially in patients affected by hypertrophic and keloid scars. Recent Advances: Advances in our understanding of mechanical forces in the wound environment enable us to target mechanical forces to minimize scar formation. Fetal wounds experience much lower resting stress when compared with adult wounds, and they heal without scars. Therapies that modulate mechanical forces in the wound environment are able to reduce scar size. Critical Issues: Increased mechanical stresses in the wound environment induce hypertrophic scarring via activation of mechanotransduction pathways. Mechanical stimulation modulates integrin, Wingless-type, protein kinase B, and focal adhesion kinase, resulting in cell proliferation and, ultimately, fibrosis. Therefore, the development of therapies that reduce mechanical forces in the wound environment would decrease the risk of developing excessive scars. Future Directions: The development of novel mechanotherapies is necessary to minimize scar formation and advance adult wound healing toward the scarless ideal. Mechanotransduction pathways are potential targets to reduce excessive scar formation, and thus, continued studies on therapies that utilize mechanical offloading and mechanomodulation are needed.

Genetic dissection of clonal lineage relationships with hydroxytamoxifen liposomes.

Targeted genetic dissection of tissues to identify precise cell populations has vast biological and therapeutic applications. Here we develop an approach, through the packaging and delivery of 4-hydroxytamoxifen liposomes (LiTMX), that enables localized induction of CreERT2 recombinase in mice. Our method permits precise, in vivo, tissue-specific clonal analysis with both spatial and temporal control. This technology is effective using mice with both specific and ubiquitous Cre drivers in a variety of tissue types, under conditions of homeostasis and post-injury repair, and is highly efficient for lineage tracing and genetic analysis. This methodology is directly and immediately applicable to the developmental biology, stem cell biology and regenerative medicine, and cancer biology fields.

Author Correction: Genetic dissection of clonal lineage relationships with hydroxytamoxifen liposomes.

In the original version of this Article, the authors inadvertently omitted Elizabeth A. Brett, who contributed to the generation of the histology figures, from the author list.This has now been corrected in both the PDF and HTML versions of the Article.

An Improved Humanized Mouse Model for Excisional Wound Healing Using Double Transgenic Mice.

Objective: Splinting full-thickness cutaneous wounds in mice has allowed for a humanized model of wound healing. Delineating the epithelial edge and assessing time to closure of these healing wounds via macroscopic visualization have remained a challenge. Approach: Double transgenic mice were created by crossbreeding K14-Cre and ROSAmT/mG reporter mice. Full-thickness excisional wounds were created in K14-Cre/ROSAmT/mG mice (n = 5) and imaged using both normal and fluorescent light on the day of surgery, and every other postoperative day (POD) until wound healing was complete. Ten blinded observers analyzed a series of images from a single representative healing wound, taken using normal or fluorescent light, to decide the POD when healing was complete. K14-Cre/ROSAmT/mG mice (n = 4) were subsequently sacrificed at the four potential days of rated wound closure to accurately determine the histological point of wound closure using microscopic fluorescence imaging. Results: Average time to wound closure was rated significantly longer in the wound series images taken using normal light, compared with fluorescent light (mean POD 13.6 vs. 11.6, *p = 0.008). Fluorescence imaging of histological samples indicated that reepithelialization was complete at 12 days postwounding. Innovation: We describe a novel technique, using double transgenic mice K14-Cre/ROSAmT/mG and fluorescence imaging, to more accurately determine the healing time of wounds in mice upon macroscopic evaluation. Conclusion: The accuracy by which wound healing can be macroscopically determined in vivo in mouse models of wound healing is significantly enhanced using K14-Cre/ROSAmT/mG double transgenic mice and fluorescence imaging.

Isolation of Live Fibroblasts by Fluorescence-Activated Cell Sorting.

Flow cytometry is a powerful tool in cell biology in that it allows real-time characterization of cellular phenotypes. Additionally, through the process of fluorescence-activated cell sorting (FACS), living cells can be isolated for future in vitro experiments, including single cell analysis. Here we describe the isolation of live fibroblasts from the dermis of the skin in mice using FACS. This method circumvents the need for ex vivo expansion in cell culture, which can alter phenotypic and functional characteristics of cells.

Excess Dermal Tissue Remodeling In Vivo: Does It Settle?

BACKGROUND: Surgical manipulation of skin may result in undesired puckering of excess tissue, which is generally assumed to settle over time. In this article, the authors address the novel question of how this excess tissue remodels. METHODS: Purse-string sutures (6-0 nylon) were placed at the midline dorsum of 22 wild-type BALB/c mice in a circular pattern marked with tattoo ink. Sutures were cinched and tied under tension in the treatment group, creating an excess tissue deformity, whereas control group sutures were tied without tension. After 2 or 4 weeks, sutures were removed. The area of tattooed skin was measured up to 56 days after suture removal. Histologic analysis was performed on samples harvested 14 days after suture removal. RESULTS: The majority of excess tissue deformities flattened within 2 days after suture removal. However, the sutured skin in the treatment group decreased in area by an average of 18 percent from baseline (n = 9), compared to a 1 percent increase in the control group (n = 10) at 14 days after suture removal (p < 0.05). This was similarly observed at 28 days (treatment, -11.7 percent; control, 4.5 percent; n = 5; p = 0.0243). Despite flattening, deformation with purse-string suture correlated with increased collagen content of skin, in addition to increased numbers of myofibroblasts. Change in area did not correlate with duration of suture placement. CONCLUSIONS: Excess dermal tissue deformities demonstrate the ability to remodel with gross flattening of the skin, increased collagen deposition, and incomplete reexpansion to baseline area. Further studies will reveal whether our findings in this mouse model translate to humans.

Rapid Isolation of BMPR-IB+ Adipose-Derived Stromal Cells for Use in a Calvarial Defect Healing Model.

Invasive cancers, major injuries, and infection can cause bone defects that are too large to be reconstructed with preexisting bone from the patient's own body. The ability to grow bone de novo using a patient's own cells would allow bony defects to be filled with adequate tissue without the morbidity of harvesting native bone. There is interest in the use of adipose-derived stromal cells (ASCs) as a source for tissue engineering because these are obtained from an abundant source: the patient's own adipose tissue. However, ASCs are a heterogeneous population and some subpopulations may be more effective in this application than others. Isolation of the most osteogenic population of ASCs could improve the efficiency and effectiveness of a bone engineering process. In this protocol, ASCs are obtained from subcutaneous fat tissue from a human donor. The subpopulation of ASCs expressing the marker BMPR-IB is isolated using FACS. These cells are then applied to an in vivo calvarial defect healing assay and are found to have improved osteogenic regenerative potential compared with unsorted cells.