The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities.

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (ß-catenin dependent) and non-canonical (ß-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Corrigendum to "Sox9 augments BMP2-induced chondrogenic differentiation by downregulating Smad7 in mesenchymal stem cells (MSCs)" [Genes & Diseases 4 (2017) 229-239].

[This corrects the article DOI: 10.1016/j.gendis.2017.10.004.].

Comparison between micro-anchor skin dressing and liquid bonding agent for elective knee arthroscopy portal closure.

OBJECTIVE: The objective of the current study was to evaluate outcomes of elective knee arthroscopy portal closure comparing two skin closure techniques. METHOD: This was a randomised controlled trial including healthy volunteers aged ≥18 years undergoing elective knee arthroscopy that used two portals. At the time of surgery, each patient's two arthroscopy portal closures were randomised to one of two closure techniques; the first technique used approximation of the skin with a micro-anchor skin dressing (BandGrip Inc., US), while the second closure technique used an absorbable suture (Biosyn Monofilament, Medtronic) and a liquid bonding agent skin closure (Dermabond, Ethicon Inc., US). Postoperative complications and patient-reported outcomes were evaluated at the first visit after knee arthroscopy and at six weeks postoperatively. RESULTS: A total of 38 patients (76 portals) were enrolled in this study. No patients reported wound complications of either portal; thus, there was no significant difference (p>0.05) in wound complication rates between the skin closure techniques. Survey questions regarding any difference in appearance and cosmesis between the closure techniques' portal sites were responded to by 15 patients, all of whom indicated no difference in appearance between the portal sites. There was also no statistically significant difference between the two closure techniques with regards to appearance. CONCLUSION: There was no significant difference in presence of wound complications or appearance between skin closure with the micro-anchor skin dressing and the absorbable suture/liquid bonding agent skin closure.

Protective Sport Bracing for Athletes With Mid-Season Shoulder Instability.

CONTEXT: In-season glenohumeral instability is a common clinical dilemma faced by physicians who care for athletes. Both nonoperative and operative management of athletes with in-season glenohumeral instability have been well described. Functional bracing remains less understood as a treatment modality. This review aims to provide an update on the most recent literature regarding the use of functional bracing for shoulder instability. EVIDENCE ACQUISITION: MEDLINE (PubMed and Ovid platforms), Web of Science, Embase, and Cochrane Database of Systemic Reviews were searched for articles available in English through June 1, 2021. The search terms shoulder brace, shoulder instability, athlete, in-season, glenohumeral instability, anterior shoulder instability, posterior shoulder instability, and bracing were used. STUDY DESIGN: Clinical review. LEVEL OF EVIDENCE: Level 3. RESULTS: Research on the clinical outcomes of functional bracing remains mixed for patients with shoulder instability. Two studies have demonstrated improved return to play with functional bracing, while 1 study demonstrated no difference in return to play between braced athletes and nonbraced athletes with anterior instability. One previous study demonstrated that prophylactic use of bilateral shoulder stabilizing braces significantly decreased time lost due to injury in athletes with posterior instability. Previous biomechanical studies have demonstrated improved proprioception with brace wear as well as successful limitation of active shoulder range of motion. CONCLUSION: Bracing in athletes with shoulder instability remains an important nonoperative treatment modality. While clinical benefits are yet to be validated through high-quality studies, preliminary results suggest a potential benefit to recovery, with minimal downsides. Nevertheless, the use of bracing remains an individual choice but is especially recommended in settings of high-risk sports for shoulder instability, such as football.

Reversibly immortalized keratinocytes (iKera) facilitate re-epithelization and skin wound healing: Potential applications in cell-based skin tissue engineering.

Skin injury is repaired through a multi-phase wound healing process of tissue granulation and re-epithelialization. Any failure in the healing process may lead to chronic non-healing wounds or abnormal scar formation. Although significant progress has been made in developing novel scaffolds and/or cell-based therapeutic strategies to promote wound healing, effective management of large chronic skin wounds remains a clinical challenge. Keratinocytes are critical to re-epithelialization and wound healing. Here, we investigated whether exogenous keratinocytes, in combination with a citrate-based scaffold, enhanced skin wound healing. We first established reversibly immortalized mouse keratinocytes (iKera), and confirmed that the iKera cells expressed keratinocyte markers, and were responsive to UVB treatment, and were non-tumorigenic. In a proof-of-principle experiment, we demonstrated that iKera cells embedded in citrate-based scaffold PPCN provided more effective re-epithelialization and cutaneous wound healing than that of either PPCN or iKera cells alone, in a mouse skin wound model. Thus, these results demonstrate that iKera cells may serve as a valuable skin epithelial source when, combining with appropriate biocompatible scaffolds, to investigate cutaneous wound healing and skin regeneration.

OUHP: an optimized universal hairpin primer system for cost-effective and high-throughput RT-qPCR-based quantification of microRNA (miRNA) expression.

MicroRNAs (miRNAs or miRs) are single-stranded, ∼22-nucleotide noncoding RNAs that regulate many cellular processes. While numerous miRNA quantification technologies are available, a recent analysis of 12 commercial platforms revealed high variations in reproducibility, sensitivity, accuracy, specificity and concordance within and/or between platforms. Here, we developed a universal hairpin primer (UHP) system that negates the use of miRNA-specific hairpin primers (MsHPs) for quantitative reverse transcription PCR (RT-qPCR)-based miRNA quantification. Specifically, we analyzed four UHPs that share the same hairpin structure but are anchored with two, three, four and six degenerate nucleotides at 3'-ends (namely UHP2, UHP3, UHP4 and UHP6), and found that the four UHPs yielded robust RT products and quantified miRNAs with high efficiency. UHP-based RT-qPCR miRNA quantification was not affected by long transcripts. By analyzing 14 miRNAs, we demonstrated that UHP4 closely mimicked MsHPs in miRNA quantification. Fine-tuning experiments identified an optimized UHP (OUHP) mix with a molar composition of UHP2:UHP4:UHP6 = 8:1:1, which closely recapitulated MsHPs in miRNA quantification. Using synthetic LET7 isomiRs, we demonstrated that the OUHP-based qPCR system exhibited high specificity and sensitivity. Collectively, our results demonstrate that the OUHP system can serve as a reliable and cost-effective surrogate of MsHPs for RT-qPCR-based miRNA quantification for basic research and precision medicine.

A Safe Interval between Preoperative Intra-articular Corticosteroid Injections and Subsequent Knee Arthroscopy.

The purpose of this study is to evaluate the influence of intra-articular corticosteroid injections prior to knee arthroscopy on the rate of postoperative infection and define a safe timing interval between intra-articular corticosteroid injections and subsequent knee arthroscopy. The PearlDiver Database was used to identify patients who underwent a knee arthroscopy from 2007 to 2017. Patients were sorted into an injection cohort if they received any intra-articular corticosteroid injections within 6 months before surgery and a control cohort if they received no such injections. The injection cohort was then stratified into subgroups based on the timing of the most recent injection. We identified two types of postoperative infection in the 6 months following surgery: a broad definition of infection using knee infection diagnoses, and a narrow definition of infection requiring surgical treatment. The effects of the timing of preoperative corticosteroid injections on the rates of postoperative infection were investigated. The rate of broadly defined postoperative infection was significantly higher in the 0 to 2 weeks injection group (6.90%, 20/290) than the control group (2.01%, 1,449/72,089, p < 0.001; odds ratio [OR]:3.61 [95% confidence interval [CI]: 2.29, 5.70]). We observed a significant difference regarding the rate of narrowly defined postoperative infection requiring surgical treatment between the 0 and 2 weeks injection group (1.38%, 4/290) and the control group (0.27%, 192/72,089, p < 0.001, OR:5.24 [95% CI: 1.94, 14.21]). No significant differences were observed between other subgroups and the control group in both types of postoperative infection. Intra-articular corticosteroid injections within 2 weeks of knee arthroscopy were statistically significantly associated with higher rates of postoperative infection. This is a Level III, retrospective comparative study.

Argonaute (AGO) proteins play an essential role in mediating BMP9-induced osteogenic signaling in mesenchymal stem cells (MSCs).

As multipotent progenitor cells, mesenchymal stem cells (MSCs) can renew themselves and give rise to multiple lineages including osteoblastic, chondrogenic and adipogenic lineages. It's previously shown that BMP9 is the most potent BMP and induces osteogenic and adipogenic differentiation of MSCs. However, the molecular mechanism through which BMP9 regulates MSC differentiation remains poorly understood. Emerging evidence indicates that noncoding RNAs, especially microRNAs, may play important roles in regulating MSC differentiation and bone formation. As highly conserved RNA binding proteins, Argonaute (AGO) proteins are essential components of the multi-protein RNA-induced silencing complexes (RISCs), which are critical for small RNA biogenesis. Here, we investigate possible roles of AGO proteins in BMP9-induced lineage-specific differentiation of MSCs. We first found that BMP9 up-regulated the expression of Ago1, Ago2 and Ago3 in MSCs. By engineering multiplex siRNA vectors that express multiple siRNAs targeting individual Ago genes or all four Ago genes, we found that silencing individual Ago expression led to a decrease in BMP9-induced early osteogenic marker alkaline phosphatase (ALP) activity in MSCs. Furthermore, we demonstrated that simultaneously silencing all four Ago genes significantly diminished BMP9-induced osteogenic and adipogenic differentiation of MSCs and matrix mineralization, and ectopic bone formation. Collectively, our findings strongly indicate that AGO proteins and associated small RNA biogenesis pathway play an essential role in mediating BMP9-induced osteogenic differentiation of MSCs.

A functional autophagy pathway is essential for BMP9-induced osteogenic differentiation of mesenchymal stem cells (MSCs).

Mesenchymal stem cells (MSCs) are capable of differentiating into bone, cartilage and adipose tissues. We identified BMP9 as the most potent osteoinductive BMP although detailed mechanism underlying BMP9-regulated osteogenesis of MSCs is indeterminate. Emerging evidence indicates that autophagy plays a critical role in regulating bone homeostasis. We investigated the possible role of autophagy in osteogenic differentiation induced by BMP9. We showed that BMP9 upregulated the expression of multiple autophagy-related genes in MSCs. Autophagy inhibitor chloroquine (CQ) inhibited the osteogenic activity induced by BMP9 in MSCs. While overexpression of ATG5 or ATG7 did not enhance osteogenic activity induced by BMP9, silencing Atg5 expression in MSCs effectively diminished BMP9 osteogenic signaling activity and blocked the expression of the osteogenic regulator Runx2 and the late marker osteopontin induced by BMP9. Stem cell implantation study revealed that silencing Atg5 in MSCs profoundly inhibited ectopic bone regeneration and bone matrix mineralization induced by BMP9. Collectively, our results strongly suggest a functional autophagy pathway may play an essential role in regulating osteogenic differentiation induced by BMP9 in MSCs. Thus, restoration of dysregulated autophagic activity in MSCs may be exploited to treat fracture healing, bone defects or osteoporosis.

Applications of Biocompatible Scaffold Materials in Stem Cell-Based Cartilage Tissue Engineering.

Cartilage, especially articular cartilage, is a unique connective tissue consisting of chondrocytes and cartilage matrix that covers the surface of joints. It plays a critical role in maintaining joint durability and mobility by providing nearly frictionless articulation for mechanical load transmission between joints. Damage to the articular cartilage frequently results from sport-related injuries, systemic diseases, degeneration, trauma, or tumors. Failure to treat impaired cartilage may lead to osteoarthritis, affecting more than 25% of the adult population globally. Articular cartilage has a very low intrinsic self-repair capacity due to the limited proliferative ability of adult chondrocytes, lack of vascularization and innervation, slow matrix turnover, and low supply of progenitor cells. Furthermore, articular chondrocytes are encapsulated in low-nutrient, low-oxygen environment. While cartilage restoration techniques such as osteochondral transplantation, autologous chondrocyte implantation (ACI), and microfracture have been used to repair certain cartilage defects, the clinical outcomes are often mixed and undesirable. Cartilage tissue engineering (CTE) may hold promise to facilitate cartilage repair. Ideally, the prerequisites for successful CTE should include the use of effective chondrogenic factors, an ample supply of chondrogenic progenitors, and the employment of cell-friendly, biocompatible scaffold materials. Significant progress has been made on the above three fronts in past decade, which has been further facilitated by the advent of 3D bio-printing. In this review, we briefly discuss potential sources of chondrogenic progenitors. We then primarily focus on currently available chondrocyte-friendly scaffold materials, along with 3D bioprinting techniques, for their potential roles in effective CTE. It is hoped that this review will serve as a primer to bring cartilage biologists, synthetic chemists, biomechanical engineers, and 3D-bioprinting technologists together to expedite CTE process for eventual clinical applications.

Notch signaling: Its essential roles in bone and craniofacial development.

Notch is a cell-cell signaling pathway that is involved in a host of activities including development, oncogenesis, skeletal homeostasis, and much more. More specifically, recent research has demonstrated the importance of Notch signaling in osteogenic differentiation, bone healing, and in the development of the skeleton. The craniofacial skeleton is complex and understanding its development has remained an important focus in biology. In this review we briefly summarize what recent research has revealed about Notch signaling and the current understanding of how the skeleton, skull, and face develop. We then discuss the crucial role that Notch plays in both craniofacial development and the skeletal system, and what importance it may play in the future.

Stem Cell-Friendly Scaffold Biomaterials: Applications for Bone Tissue Engineering and Regenerative Medicine.

Bone is a dynamic organ with high regenerative potential and provides essential biological functions in the body, such as providing body mobility and protection of internal organs, regulating hematopoietic cell homeostasis, and serving as important mineral reservoir. Bone defects, which can be caused by trauma, cancer and bone disorders, pose formidable public health burdens. Even though autologous bone grafts, allografts, or xenografts have been used clinically, repairing large bone defects remains as a significant clinical challenge. Bone tissue engineering (BTE) emerged as a promising solution to overcome the limitations of autografts and allografts. Ideal bone tissue engineering is to induce bone regeneration through the synergistic integration of biomaterial scaffolds, bone progenitor cells, and bone-forming factors. Successful stem cell-based BTE requires a combination of abundant mesenchymal progenitors with osteogenic potential, suitable biofactors to drive osteogenic differentiation, and cell-friendly scaffold biomaterials. Thus, the crux of BTE lies within the use of cell-friendly biomaterials as scaffolds to overcome extensive bone defects. In this review, we focus on the biocompatibility and cell-friendly features of commonly used scaffold materials, including inorganic compound-based ceramics, natural polymers, synthetic polymers, decellularized extracellular matrix, and in many cases, composite scaffolds using the above existing biomaterials. It is conceivable that combinations of bioactive materials, progenitor cells, growth factors, functionalization techniques, and biomimetic scaffold designs, along with 3D bioprinting technology, will unleash a new era of complex BTE scaffolds tailored to patient-specific applications.

Complication rates following hip arthroscopy in the ambulatory surgical center.

There has been an increase in the number of hip arthroscopy procedures performed in the outpatient setting. The purpose of this study was to query a national database to compare post-operative adverse events between hip arthroscopy procedures performed in hospital based outpatient departments (HOPD) versus ASC's. The Humana Claims Database was queried for all patients undergoing hip arthroscopy performed between 2007 and 2016, using the PearlDiver supercomputer. The study population was divided into two cohorts based on the surgical setting, ASC or HOPD. Complications of interest occurring within 90 days after surgery included Center for Medicare and Medicaid Services (CMS)-reportable complications, readmission, and return to the operating room. Visits to the emergency department after 7 days of surgery was also studied. Univariate comparisons between ASC and HOPD groups were drawn with chi-square tests for categorical variables and t-tests for continuous variables. Logistic regression models were created to determine the association between surgical setting and primary outcomes. Rates of 90-day CMS-reportable complications (2.95% vs 2.17%%; p = 0.193), 90-day readmission (4.95% vs 4.25%; p = 0.370) and return to the operating room within 90 days (0.07% vs 0.2%; p = 0.286) were not significantly different between groups. Rate of visits to the emergency department within 7 days was not statistically different between groups (2.57% vs 3.03%; p = 0.458). With the ASC group as reference, no statistically significant association between an outcome and surgical setting was detected after adjusting for confounding factors including comorbidity burden. These findings provide reassurance to providers who perform these procedures in either surgical setting.

The effect of surgical setting on anterior cruciate ligament reconstruction outcomes.

Objective: Ambulatory surgical centers (ASC's) have emerged as an alternative to the traditional hospital- based outpatient department (HOPD). We aim to determine the effect of surgical setting on adverse events following anterior cruciate ligament reconstruction (ACLR).Methods: The Humana Claims Database was queried for all patients undergoing ACLR in the HOPD or ASC setting, using the PearlDiver supercomputer. To eliminate selection bias in our study, the HOPD and ASC cohorts were propensity score matched on baseline demographics, comorbidities, and operative factors. Comparisons between the matched cohorts were made using chi-square tests. Logistic regression models were created to determine the effect of surgical setting on adverse events.Results: A total of 13,647 patients were queried in our study, 5,298 of whom underwent surgery in an ASC and 8,349 of whom underwent surgery in an HOPD. Analysis of the post-matched cohort revealed no differences between cohorts for mechanical failure, nerve injury, pulmonary embolism, septic joint, wound infection, revision surgery and readmission. Rates of deep vein thrombosis (1.18% vs 1.84%; p = .03) were significantly lower in the ASC group. On logistic regression, ASC was associated with decreased risk for deep vein thrombosis (.87, .83-.93) and pulmonary embolism (.85, .78-.95).Conclusion: ACLR performed in ASC is associated with reduced risk of venous thromboembolism and no difference in surgical morbidity and readmissions versus ACLR performed in HOPD. Development of a standardized algorithm for patient selection in the ASC setting is needed to preserve acceptability of ASC-based ACLR in cost-savings and patient safety models.

The wonders of BMP9: From mesenchymal stem cell differentiation, angiogenesis, neurogenesis, tumorigenesis, and metabolism to regenerative medicine.

Although bone morphogenetic proteins (BMPs) initially showed effective induction of ectopic bone growth in muscle, it has since been determined that these proteins, as members of the TGF-ß superfamily, play a diverse and critical array of biological roles. These roles include regulating skeletal and bone formation, angiogenesis, and development and homeostasis of multiple organ systems. Disruptions of the members of the TGF-ß/BMP superfamily result in severe skeletal and extra-skeletal irregularities, suggesting high therapeutic potential from understanding this family of BMP proteins. Although it was once one of the least characterized BMPs, BMP9 has revealed itself to have the highest osteogenic potential across numerous experiments both in vitro and in vivo, with recent studies suggesting that the exceptional potency of BMP9 may result from unique signaling pathways that differentiate it from other BMPs. The effectiveness of BMP9 in inducing bone formation was recently revealed in promising experiments that demonstrated efficacy in the repair of critical sized cranial defects as well as compatibility with bone-inducing bio-implants, revealing the great translational promise of BMP9. Furthermore, emerging evidence indicates that, besides its osteogenic activity, BMP9 exerts a broad range of biological functions, including stem cell differentiation, angiogenesis, neurogenesis, tumorigenesis, and metabolism. This review aims to summarize our current understanding of BMP9 across biology and the body.

Association of Injury Energy Level and Neurovascular Injury Following Knee Dislocation.

OBJECTIVE: To describe the associations between mechanism of injury energy level and neurovascular injury (NVI) following knee dislocation (KD) using a large representative sample of trauma patients and to examine risk factors within these groups. DESIGN: Retrospective cohort study. SETTING: Trauma centers participating in the American College of Surgeons National Trauma Data Bank. PARTICIPANTS: Adult patients with KD without lower extremity fracture. INTERVENTION: Patients were grouped as ultra-low, low, or high-energy based on injury mechanism. Univariate/multivariate analyses assessed associations of energy level with NVI and of patient characteristics with NVI within energy-level groups. MAIN OUTCOME MEASUREMENTS: Rate of nerve and blood vessel injury. RESULTS: One hundred twenty-four patients with KD were identified; 181 sustained ultra-low-energy mechanisms, 275 low-energy, and 868 high-energy. Nerve injury occurred in 6% of ultra-low-energy injuries, 7% in low-energy, and 3% in high-energy (P = 0.03). Vessel injury occurred in 21% of ultra-low-energy injuries, 17% in low-energy, and 13% in high-energy (P = 0.01). On multivariate analyses, obesity was associated with nerve injury in the ultra-low-energy group (OR 4.9; 95% CI 1.0-24.0) but not with other energy levels. Obesity was also associated with vessel injury in the ultra-low-energy group (OR 4.0; 95% CI 1.6-9.7). Smoking, hypertension, and diabetes were not associated with NVI. CONCLUSIONS: NVI following KD is more common after lower energy-level mechanisms. Obesity is associated with NVI in lower energy-level mechanisms. Physicians should be vigilant in screening for NVI in the setting of KD even with seemingly benign mechanisms of injury, especially in patients with obesity. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Endoscopic Repair of Partial-Thickness Undersurface Tears of the Abductor Tendon: Clinical Outcomes With Minimum 2-Year Follow-up.

PURPOSE: To report the minimum 2-year outcomes of transtendinous repair of partial-thickness undersurface tears of the abductor tendon using patient-reported outcomes (PROs), visual analog scale (VAS) scores, and patient satisfaction scores. METHODS: All patients who underwent endoscopic transtendinous gluteus medius repair between October 2009 and May 2013 at 1 institution were prospectively evaluated. The exclusion criteria consisted of less than 2 years' follow-up, previous hip surgery, inflammatory arthritis, open surgery, full-thickness abductor tear, and Workers' Compensation patients. All patients underwent a documented preoperative physical examination with strength testing (scale of 0-5) and observation of their gait. Patient satisfaction and PRO scores were recorded preoperatively; at 3 months postoperatively; and at 1, 2, 5, and 10 years after surgery. The PRO scores collected were the modified Harris Hip Score, Hip Outcome Score-Activities of Daily Living Subscale, Hip Outcome Score-Sports-Specific Subscale, Non-arthritis Hip Score, and VAS score. Preoperative strength and gait were compared with latest follow-up. RESULTS: There were 25 patients who fit our criteria. Significant improvement in PRO scores were shown for the modified Harris Hip Score, Hip Outcome Score-Activities of Daily Living Subscale, Hip Outcome Score-Sports-Specific Subscale, Non-arthritis Hip Score, and VAS score from 54.9 to 76.2, from 50.2 to 80.6, from 30.1 to 67.3, from 51.9 to 82.4, and from 7.1 to 2.7, respectively (P < .001). Before surgery, 11 patients had objective weakness; 7 of these patients moved up at least 1 strength grade by final follow-up. Preoperatively, 14 patients had a Trendelenburg gait; 12 of them had a normal gait at latest follow-up (P < .001). The average patient satisfaction rating was 7.5. There were no revision surgical procedures, and no complications were noted. CONCLUSIONS: Partial-thickness undersurface tears of the abductor can be treated successfully with endoscopic transtendinous repair preserving the intact attachment of the superficial fibers of the gluteus medius. We recommend this treatment for partial undersurface tears recalcitrant to nonoperative treatment because patients showed clinical benefit at greater than 2 years' follow-up that exceeded substantial clinical benefit and the minimal clinically important difference. LEVEL OF EVIDENCE: Level IV, case series.

Adenovirus-Mediated Gene Delivery: Potential Applications for Gene and Cell-Based Therapies in the New Era of Personalized Medicine.

With rapid advances in understanding molecular pathogenesis of human diseases in the era of genome sciences and systems biology, it is anticipated that increasing numbers of therapeutic genes or targets will become available for targeted therapies. Despite numerous setbacks, efficacious gene and/or cell-based therapies still hold the great promise to revolutionize the clinical management of human diseases. It is wildly recognized that poor gene delivery is the limiting factor for most in vivo gene therapies. There has been a long-lasting interest in using viral vectors, especially adenoviral vectors, to deliver therapeutic genes for the past two decades. Among all currently available viral vectors, adenovirus is the most efficient gene delivery system in a broad range of cell and tissue types. The applications of adenoviral vectors in gene delivery have greatly increased in number and efficiency since their initial development. In fact, among over 2,000 gene therapy clinical trials approved worldwide since 1989, a significant portion of the trials have utilized adenoviral vectors. This review aims to provide a comprehensive overview on the characteristics of adenoviral vectors, including adenoviral biology, approaches to engineering adenoviral vectors, and their applications in clinical and pre-clinical studies with an emphasis in the areas of cancer treatment, vaccination and regenerative medicine. Current challenges and future directions regarding the use of adenoviral vectors are also discussed. It is expected that the continued improvements in adenoviral vectors should provide great opportunities for cell and gene therapies to live up to its enormous potential in personalized medicine.

Sox9 augments BMP2-induced chondrogenic differentiation by downregulating Smad7 in mesenchymal stem cells (MSCs).

Cartilage injuries caused by arthritis or trauma pose formidable challenges for effective clinical management due to the limited intrinsic proliferative capability of chondrocytes. Autologous stem cell-based therapies and transgene-enhanced cartilage tissue engineering may open new avenues for the treatment of cartilage injuries. Bone morphogenetic protein 2 (BMP2) induces effective chondrogenesis of mesenchymal stem cells (MSCs) and can thus be explored as a potential therapeutic agent for cartilage defect repair. However, BMP2 also induces robust endochondral ossification. Although the precise mechanisms through which BMP2 governs the divergence of chondrogenesis and osteogenesis remain to be fully understood, blocking endochondral ossification during BMP2-induced cartilage formation may have practical significance for cartilage tissue engineering. Here, we investigate the role of Sox9-donwregulated Smad7 in BMP2-induced chondrogenic differentiation of MSCs. We find that overexpression of Sox9 leads to a decrease in BMP2-induced Smad7 expression in MSCs. Sox9 inhibits BMP2-induced expression of osteopontin while enhancing the expression of chondrogenic marker Col2a1 in MSCs. Forced expression of Sox9 in MSCs promotes BMP2-induced chondrogenesis and suppresses BMP2-induced endochondral ossification. Constitutive Smad7 expression inhibits BMP2-induced chondrogenesis in stem cell implantation assay. Mouse limb explant assay reveals that Sox9 expands BMP2-stimulated chondrocyte proliferating zone while Smad7 promotes BMP2-intitated hypertrophic zone of the growth plate. Cell cycle analysis indicates that Smad7 induces significant early apoptosis in BMP2-stimulated MSCs. Taken together, our results strongly suggest that Sox9 may facilitate BMP2-induced chondrogenesis by downregulating Smad7, which can be exploited for effective cartilage tissue engineering.

Immortalized Mouse Achilles Tenocytes Demonstrate Long-Term Proliferative Capacity While Retaining Tenogenic Properties.

Investigating the cellular processes underlying tendon healing can allow researchers to improve long-term outcomes after injury. However, conducting meaningful studies to uncover the injury healing mechanism at cellular and molecular levels remains challenging. This is due to the inherent difficulty in isolating, culturing, and expanding sufficient primary tenocytes, due to their limited proliferative capacity and short lifespan. In this study, we sought to establish a novel line of immortalized mouse Achilles tenocytes (iMATs) with primary tenocyte properties, but increased proliferative capacity suitable for extensive in vitro experimentation. We show that isolated primary mouse Achilles tenocytes (pMATs) can be effectively immortalized using a piggyBac transposon expressing SV40 large T antigen flanked by FLP recombination target site (FRT). The resulting iMATs exhibit markedly greater proliferation and survival, which can be reversed with FLP recombinase. Furthermore, iMATs express the same set of tendon-specific markers as that of primary cells, although in lower levels, and respond similarly to exogenous stimulation with bone morphogenetic protein 13 (BMP13) as has been previously reported with pMATs. Taken together, our results suggest that iMATs acquire long-term proliferative capacity while maintaining tenogenic properties. We believe that iMATs are a suitable model for studying not only the native cellular processes involved in injury and healing, but also potential therapeutic agents that may augment the stability of tendon repair.