Correction of a mineralization defect by overexpression of a wild-type cDNA for COL1A1 in marrow stromal cells (MSCs) from a patient with osteogenesis imperfecta: a strategy for rescuing mutations that produce dominant-negative protein defects

Mesenchymal stem cells in the treatment of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a disease caused by mutations in different genes resulting in mild, severe, or lethal forms. With no cure, researchers have investigated the use of cell therapy to correct the underlying molecular defects of OI. Mesenchymal stem cells (MSCs) are of particular interest because of their differentiation capacity, immunomodulatory effects, and their ability to migrate to sites of damage. MSCs can be isolated from different sources, expanded in culture, and have been shown to be safe in numerous clinical applications. This review summarizes the preclinical and clinical studies of MSCs in the treatment of OI. Altogether, the culmination of these studies show that MSCs from different sources: 1) are safe to use in the clinic, 2) migrate to fracture sites and growth sites in bone, 3) engraft in low levels, 4) improve clinical outcome but have a transient effect, 5) have a therapeutic effect most likely due to paracrine mechanisms, and 6) have a reduced therapeutic potential when isolated from patients with OI.

Ginsenoside Rc Promotes Bone Formation in Ovariectomy-Induced Osteoporosis In Vivo and Osteogenic Differentiation In Vitro

Ginsenoside Rc is one of the active components used in traditional Chinese medicine. We aim to explore how ginsenoside Rc can be used in the treatment of osteoporosis. Micro-CT demonstrated that the treatment of ovariectomized (OVX) mice with ginsenoside Rc significantly inhibited the decrease in bone mineral density, bone volumetric fraction, and trabecular number, and the increase in trabecular separation. Histological staining, qRT-PCR, and Western blot demonstrated that ginsenoside Rc enhances the microstructure of trabecular bone, and promotes the expression of bone formation-related genes. Alkaline phosphatase (ALP) staining, Alizarin Red staining, qRT-PCR, and Western blotting demonstrated that ginsenoside Rc dose-dependently promoted the osteogenic differentiation of MC3T3-E1 cells. A ginsenoside Rc-induced increase in the expression of β-catenin, p-GSK-3β, collagen-1, ALP, and RUNX-2 family transcription factor-2 was significantly attenuated upon 10 μM XAV-939 treatment, while the decrease in the expression of GSK-3β and p-β-catenin was significantly enhanced. Ginsenoside Rc promotes bone formation in ovariectomy-induced osteoporosis in vivo and promotes osteogenic differentiation in vitro via the Wnt/β-catenin signaling pathway.

Ponicidin Treatment Improved the Cell Proliferation, Differentiation, and Calcium Mineralization on the Osteoblast-Like MG-63 Cells

Osteoporosis is a general bone-related ailment characterized by reduced bone density and quality, elevated bone fragility, and fractures. It was reported that both aged men and women has an increased risks of osteoporosis. The current research work focused to unveil the beneficial roles of ponicidin treatment in the proliferation and calcium deposition on the osteoblast-like MG-63 cells. The effect of 5 and 10 µg/ml of ponicidin on the cell proliferation was assessed. The viability of ponicidin-supplemented MG-63 cells was inspected by MTT test. The contents of osteocalcin, collagen, and ALP activity in the ponicidin administered cells were assessed by kits. The level of calcium mineralization was examined by ARS staining technique. The ponicidin treatment remarkably improved the proliferation of MG-63 cells. The ponicidin did not affect the MG-63 cells viability but promoted its viability 24- and 48-h treatment. The contents of osteocalcin, collagen, and ALP activity in the 5 and 10 µg/ml of ponicidin-supplemented MG-63 cells were found increased than the control cells. The ponicidin also increased the level of calcium deposition in MG-63 cells, which is assessed by ARS staining. In conclusion, it was clear that ponicidin improved the proliferation and calcium mineralization in a MG-63 cells. Therefore, it was clear that ponicidin has helpful roles on the new bone development as a hopeful therapeutic candidate to treat the bone-related disease like osteoporosis.

Augmenting and directing long-range CRISPR-mediated activation in human cells

Epigenetic editing is an emerging technology that uses artificial transcription factors (aTFs) to regulate expression of a target gene. Although human genes can be robustly upregulated by targeting aTFs to promoters, the activation induced by directing aTFs to distal transcriptional enhancers is substantially less robust and consistent. Here we show that long-range activation using CRISPR-based aTFs in human cells can be made more efficient and reliable by concurrently targeting an aTF to the target gene promoter. We used this strategy to direct target gene choice for enhancers capable of regulating more than one promoter and to achieve allele-selective activation of human genes by targeting aTFs to single-nucleotide polymorphisms embedded in distally located sequences. Our results broaden the potential applications of the epigenetic editing toolbox for research and therapeutics.

Modification of COL1A1 in Autologous Adipose Tissue-Derived Progenitor Cells Rescues the Bone Phenotype in a Mouse Model of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a congenital genetic disorder mainly manifested as bone fragility and recurrent fracture. Mutation of COL1A1/COL1A2 genes encoding the type I collagen are most responsible for the clinical patients. Allogenic mesenchymal stem cells (MSCs) provide the potential to treat OI through differentiation into osteoblasts. Autologous defective MSCs have not been utilized in OI treatment mainly because of their impaired osteogenesis, but the latent mechanism has not been well understood. Here, the relative signaling abnormality of adipose-derived mesenchymal stem cells (ADSCs) isolated from OI type I mice (Col1a1^+/-365 mice) was explored. Autologous ADSCs transfected by retrovirus carrying human COL1A1 gene was first utilized in OI therapy. The results showed that decreased activity of Yes-associated protein (YAP) due to hyperactive upstream Hippo kinases greatly contributed to the weakened bone-forming capacity of defective ADSCs. Recovered collagen synthesis of autologous ADSCs by COL1A1 gene modification normalized Hippo/YAP signaling and effectively rescued YAP-mediated osteogenesis. And the COL1A1 gene engineered autologous ADSCs efficaciously improved the microstructure, enhanced the mechanical properties and promoted bone formation of Col1a1^+/-365 mice after femoral bone marrow cavity delivery and might serve as an alternative source of stem cells in OI treatment. © 2021 American Society for Bone and Mineral Research (ASBMR).

Clinical Application of Bone Marrow Mesenchymal Stem/Stromal Cells to Repair Skeletal Tissue

There has been an escalation in reports over the last decade examining the efficacy of bone marrow derived mesenchymal stem/stromal cells (BMSC) in bone tissue engineering and regenerative medicine-based applications. The multipotent differentiation potential, myelosupportive capacity, anti-inflammatory and immune-modulatory properties of BMSC underpins their versatile nature as therapeutic agents. This review addresses the current limitations and challenges of exogenous autologous and allogeneic BMSC based regenerative skeletal therapies in combination with bioactive molecules, cellular derivatives, genetic manipulation, biocompatible hydrogels, solid and composite scaffolds. The review highlights the current approaches and recent developments in utilizing endogenous BMSC activation or exogenous BMSC for the repair of long bone and vertebrae fractures due to osteoporosis or trauma. Current advances employing BMSC based therapies for bone regeneration of craniofacial defects is also discussed. Moreover, this review discusses the latest developments utilizing BMSC therapies in the preclinical and clinical settings, including the treatment of bone related diseases such as Osteogenesis Imperfecta.

Whole genome sequence analysis reveals genetic structure and X-chromosome haplotype structure in indigenous Chinese pigs

Chinese indigenous pigs exhibit considerable phenotypic diversity, but their population structure and the genetic basis of agriculturally important traits need further exploration. Here, we sequenced the whole genomes of 24 individual pigs representing 22 breeds distributed throughout China. For comparison with European and commercial breeds (one pig per breed), we included seven published pig genomes with our new genomes for analyses. Our results showed that breeds grouped together based on morphological classifications are not necessarily more genetically similar to each other than to breeds from other groups. We found that genetic material from European pigs likely introgressed into five Chinese breeds. We have identified two new subpopulations of domestic pigs that encompass morphology-based criteria in China. The Southern Chinese subpopulation comprises the classical South Chinese Type and part of the Central China Type. In contrast, the Northern Chinese subpopulation comprises the North China Type, the Lower Yangtze River Basin Type, the Southwest Type, the Plateau Type, and the remainder of the Central China Type. Eight haplotypes and two recombination sites were identified within a conserved 40.09 Mb linkage-disequilibrium (LD) block on the X chromosome. Potential candidate genes (LEPR, FANCC, COL1A1, and PCCA) influencing body size were identified. Our findings provide insights into the phylogeny of Chinese indigenous pig breeds and benefit gene mining efforts to improve major economic traits.

Effects of ginsenosides on bone remodelling for novel drug applications: a review

BACKGROUND

Ginsenosides are pharmacologically active compounds that are often extracted from the Panax plant for their medicinal properties. Ginsenosides have multiple effects, including antitumor effects which have been widely studied. In recent years, studies have found that ginsenosides promote proliferation and osteogenesis of osteoblast-related cells, as well as inhibit the activity of osteoclasts.

MAIN BODY

We briefly introduces the molecules and BMP, WNT, and RANKL signalling pathways involved in bone formation and bone resorption. Next, recent studies on the mechanism of action of ginsenosides in bone remodelling are reviewed from three perspectives: the effects on proliferation of osteoblast-related cells, effects on osteogenesis and effects on osteoclasts. To expedite the development of drugs containing ginsenosides, we summarize the multiple beneficial roles of various types of ginsenosides in bone remodelling; including the promotion of bone formation, inhibition of bone resorption, and anti-inflammatory and antioxidant effects.

CONCLUSION

Many ginsenosides can promote bone formation and inhibit bone resorption, such as Rb1, Rb2 and Re. Ginsenosides have the potential to be new drugs for the treatment of osteoporosis, promote fracture healing and are strong candidates for cytokines in the tissue-engineered bone. This review provides a theoretical basis for clinical drug applications and proposes several future directions for exploring the beneficial role of ginseng compounds in bone remodelling.

A simple and highly efficient method for transduction of human adipose-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into a wide range of cell types and provide a potential to transfer therapeutic protein in vivo, making them valuable candidates for gene therapy and cell therapy. However, using MSCs in in vivo is limited due to the low rate of transfection and transduction efficacy. Therefore, developing methods to efficiently transfer genes into MSCs would provide a number of opportunities for using them in the clinic. Here, we introduce a simple and robust method for efficient transduction of human adipose-derived MSCs by modification under the culture condition of human embryonic kidney cells 293 (HEK293T) and MSCs. Moreover, as a transduction enhancer, polybrene was replaced with Lipofectamine, a cationic lipid. Therefore, we showed that transduction of primary cells can be increased efficiently by modifying the culture condition.

Extracellular vesicles released from mesenchymal stromal cells stimulate bone growth in osteogenesis imperfecta

BACKGROUND

Systemic infusion of mesenchymal stromal cells (MSCs) has been shown to induce acute acceleration of growth velocity in children with osteogenesis imperfecta (OI) despite minimal engraftment of infused MSCs in bones. Using an animal model of OI we have previously shown that MSC infusion stimulates chondrocyte proliferation in the growth plate and that this enhanced proliferation is also observed with infusion of MSC conditioned medium in lieu of MSCs, suggesting that bone growth is due to trophic effects of MSCs. Here we sought to identify the trophic factor secreted by MSCs that mediates this therapeutic activity.

METHODS

To examine whether extracellular vesicles (EVs) released from MSCs have therapeutic activity, EVs were isolated from MSC conditioned medium by ultracentrifugation. To further characterize the trophic factor, RNA or microRNA (miRNA) within EVs was depleted by either ribonuclease (RNase) treatment or suppressing miRNA biogenesis in MSCs. The functional activity of these modified EVs was evaluated using an in vitro chondrocyte proliferation assay. Finally, bone growth was evaluated in an animal model of OI treated with EVs.

RESULTS

We found that infusion of MSC-derived EVs stimulated chondrocyte proliferation in the growth plate, resulting in improved bone growth in a mouse model of OI. However, infusion of neither RNase-treated EVs nor miRNA-depleted EVs enhanced chondrocyte proliferation.

CONCLUSION

MSCs exert therapeutic effects in OI by secreting EVs containing miRNA, and EV therapy has the potential to become a novel cell-free therapy for OI that will overcome some of the current limitations in MSC therapy.

Ginsenoside Rg1 promotes osteogenic differentiation of rBMSCs and healing of rat tibial fractures through regulation of GR-dependent BMP-2/SMAD signaling

Fracture healing is closely related to the number and activity of bone marrow mesenchymal stem cells (BMSCs) near the fracture site. The present study was to investigate the effect of Rg1 on osteogenic differentiation of cultured BMSCs and related mechanisms and on the fracture healing in a fracture model. In vitro experiments showed that Rg1 promoted the proliferation and osteogenic differentiation of BMSCs. Western blot analyses demonstrated that Rg1 promoted osteogenic differentiation of BMSCs through the glucocorticoid receptor (GR)-dependent BMP-2/Smad signaling pathway. In vivo, X-ray examination showed that callus growth in rats treated with Rg1 was substantially faster than that in control rats after fracture. The results of H&E and Safranin-O/Fast Green staining revealed that, compared with controls, rats in the Rg1 treatment group had a significantly higher proportion of trabecular bone but a much lower proportion of fibers and cartilage components inside the callus. Micro-CT suggested that bone mineral density (BMD), percent bone volume (BV/TV), trabecular number (Tb.N), and trabecular thickness (Tb.Th) were significantly increased in the treatment group, whereas trabecular separation (Tb.Sp) was significantly reduced. Thus, Rg1 promotes osteogenic differentiation by activating the GR/BMP-2 signaling pathway, enhances bone calcification, and ultimately accelerates the fracture healing in rats.

Research using Mesenchymal Stem/Stromal Cells: quality metric towards developing a reference material

Mesenchymal stem/stromal cells (MSCs) have been extensively investigated for their regenerative, immune-modulatory, and wound healing properties. While the laboratory studies have suggested that MSC's have a unique potential for modulating the etiopathology of multiple diseases, the results from clinical trials have not been encouraging or reproducible. One of the explanations for such variability is explained by the "art" of isolating and propagating MSCs. Therefore, establishing more than minimal criteria to define MSC would help understand best protocols to isolate, propagate and deliver MSCs. Developing a calibration standard, a database and a set of functional tests would be a better quality metric for MSCs. In this review, we discuss the importance of selecting a standard, issues associated with coming up with such a standard and how these issues can be mitigated.

Autologous implantation of BMP2-expressing dermal fibroblasts to improve bone mineral density and architecture in rabbit long bones

Cell-mediated gene therapy may treat bone fragility disorders. Dermal fibroblasts (DFb) may be an alternative cell source to stem cells for orthopedic gene therapy because of their rapid cell yield and excellent plasticity with bone morphogenetic protein-2 (BMP2) gene transduction. Autologous DFb or BMP2-expressing autologous DFb were administered in twelve rabbits by two delivery routes; a transcortical intra-medullar infusion into tibiae and delayed intra-osseous injection into femoral drill defects. Both delivery methods of DFb-BMP2 resulted in a successful cell engraftment, increased bone volume, bone mineral density, improved trabecular bone microarchitecture, greater bone defect filling, external callus formation, and trabecular surface area, compared to non-transduced DFb or no cells. Cell engraftment within trabecular bone and bone marrow tissue was most efficiently achieved by intra-osseous injection of DFb-BMP2. Our results suggested that BMP2-expressing autologous DFb have enhanced efficiency of engraftment in target bones resulting in a measurable biologic response by the bone of improved bone mineral density and bone microarchitecture. These results support that autologous implantation of DFb-BMP2 warrants further study on animal models of bone fragility disorders, such as osteogenesis imperfecta and osteoporosis to potentially enhance bone quality, particularly along with other gene modification of these diseases.

Effect of Intra-Medullar and Intra-Venous Infusions of Mesenchymal Stem Cells on Cell Engraftment by In-Vivo Cell Tracking and Osteoinductivity in Rabbit Long Bones: A Pilot Study

OBJECTIVE

Stem cell therapy can be an efficacious treatment option for bone fragility disorders (eg, osteogenesis imperfecta, disuse osteopenia, and osteoporosis), and successful cell therapy application may be dependent on optimal cell engraftment in target bones. The objective of this study was to compare the efficiency of intra-medullar and intra-venous delivery of mesenchymal stem cells (MSC) to improve cell engraftment rate, bone mineral density, and micro-architecture.

METHODS

By using six healthy juvenile New Zealand White rabbits, MSC were isolated from cancellous bone harvests and confirmed to have osteogenic capacity by inducing ectopic bone formation. The MSC were cultured, transduced by foamy viral vectors with marker genes for in vivo cell tracking, and expanded. All rabbits had one randomly selected limb receive intra-medullar infusion of 3×10⁷ to 1×10⁸ autologous MSC in the distal femur or the distal femur and proximal tibia. Two of six rabbits also received an intra-venous MSC infusion. At 28 days, MSC bone engraftment was assessed by PCR and the bone density and microstructure assessed by computed tomography and histomorphometry.

RESULTS

The intra-medullar-infused MSC were detected in epiphysis or diaphysis of the distal femurs and/or proximal tibiae. Infused MSC comprised 0.01 to 0.3% of all cells in the bone tissues. The intra-venous-infused MSC were not detected in any location. Neither intra-medullar nor intra-venous MSC infusion altered bone volume, bone mineral density, or cortical bone porosity/thickness. Systemic biodistribution of intra-medullar-infused MSC was not evident.

CONCLUSIONS

Our results indicated that intra-medullar infusion can be an effective cell delivery route for stem cell therapy potentially for orthopedic disorders, in preference to systemic administration. Further research is warranted to demonstrate an efficacy of intra-medullar MSC infusion on bone density and micro-architecture using animal models of bone disorders.

Molecular mechanisms of mesenchymal stem cell differentiation towards osteoblasts

Bone is a dynamic tissue that is constantly renewed by the coordinated action of two cell types, i.e., the bone-resorbing osteoclasts and the bone-forming osteoblasts. However, in some circumstances, bone regeneration exceeds bone self repair capacities. This is notably often the case after bone fractures, osteolytic bone tumor surgery, or osteonecrosis. In this regard, bone tissue engineering with autologous or allogenic mesenchymal stem cells (MSCs) is been widely developed. MSCs can be isolated from bone marrow or other tissues such as adipose tissue or umbilical cord, and can be implanted in bone defects with or without prior amplification and stimulation. However, the outcome of most pre-clinical studies remains relatively disappointing. A better understanding of the successive steps and molecular mechanisms involved in MSC-osteoblastic differentiation appears to be crucial to optimize MSC-bone therapy. In this review, we first present the important growth factors that stimulate osteoblastogenesis. Then we review the main transcription factors that modulate osteoblast differentiation, and the microRNAs (miRs) that inhibit their expression. Finally, we also discuss articles dealing with the use of these factors and miRs in the development of new bone MSC therapy strategies. We particularly focus on the studies using human MSCs, since significant differences exist between osteoblast differentiation mechanisms in humans and mice for instance.

Recommendations and considerations for the use of biologics in orthopedic surgery

Reconstruction of extensive bone defects remains technically challenging and has considerable medical and financial impact on our society. Surgical procedures often require a bone/substitute graft to enhance and accelerate bone repair. Bone autografts are associated with morbidity related to bone harvesting and are limited in quantity. Alternatively, bone allografts expose the patient to the risk of transmission of infectious disease. Synthetic bone graft substitutes, such as calcium sulfates, hydroxyapatite, tricalcium phosphate, and combinations, circumvent some of the disadvantages of auto- and allografts, but have limited indications. Biomedical research has made possible the stimulation of the body's own healing mechanisms, either by delivering exogenous growth factors locally, or by stimulating their local production by gene transfer. Among all known factors having osteoinductive properties, only two bone morphogenetic proteins (for specific indications) and demineralized bone matrix have been approved for clinical use. In addition, ongoing research is exploring the efficacy of cell therapy and tissue engineering. The present report examines the composition, biological properties, indications, clinical experience and regulations of several of the biotherapeutics employed for bone reconstruction.

Differential expression of surface markers in mouse bone marrow mesenchymal stromal cell subpopulations with distinct lineage commitment

Bone marrow mesenchymal stromal cells (BM MSCs) represent a heterogeneous population of progenitors with potential for generation of skeletal tissues. However the identity of BM MSC subpopulations is poorly defined mainly due to the absence of specific markers allowing in situ localization of those cells and isolation of pure cell types. Here, we aimed at characterization of surface markers in mouse BM MSCs and in their subsets with distinct differentiation potential. Using conditionally immortalized BM MSCs we performed a screening with 176 antibodies and high-throughput flow cytometry, and found 33 markers expressed in MSCs, and among them 3 were novel for MSCs and 13 have not been reported for MSCs from mice. Furthermore, we obtained clonally derived MSC subpopulations and identified bipotential progenitors capable for osteo- and adipogenic differentiation, as well as monopotential osteogenic and adipogenic clones, and thus confirmed heterogeneity of MSCs. We found that expression of CD200 was characteristic for the clones with osteogenic potential, whereas SSEA4 marked adipogenic progenitors lacking osteogenic capacity, and CD140a was expressed in adipogenic cells independently of their efficiency for osteogenesis. We confirmed our observations in cell sorting experiments and further investigated the expression of those markers during the course of differentiation. Thus, our findings provide to our knowledge the most comprehensive characterization of surface antigens expression in mouse BM MSCs to date, and suggest CD200, SSEA4 and CD140a as markers differentially expressed in distinct types of MSC progenitors.

Stem cells and regenerative medicine: accomplishments to date and future promise

More than 50 years have passed since the first allogeneic hematopoietic stem cell transplant in patients; however, the promise of other stem cell populations for tissue replacement and repair remains unachieved. When considering cell-based interventions for personalized medicine, the factors influencing therapeutic success and safety are more complicated than for traditional small-molecule pharmacological agents and protein biologics. Failure to progress personalized stem cell therapies to the clinic has resulted from complications that include an incomplete understanding of developmental programs and the diversity of host-donor interactions. In order to more rapidly extend the use of stem cells to the clinic, a better understanding of the different stem cell sources and the implications of their host interactions is required. In this review, we introduce the currently available sources and highlight recent literature that instructs the potential and limitations of their use.

Gene therapy: implications for craniofacial regeneration

Gene therapy in the craniofacial region provides a unique tool for delivery of DNA to coordinate protein production in both time and space. The drive to bring this technology to the clinic is derived from the fact that more than 85% of the global population may at one time require repair or replacement of a craniofacial structure. This need ranges from mild tooth decay and tooth loss to temporomandibular joint disorders and large-scale reconstructive surgery. Our ability to insert foreign DNA into a host cell has been developing since the early uses of gene therapy to alter bacterial properties for waste cleanup in the 1980s followed by successful human clinical trials in the 1990s to treat severe combined immunodeficiency. In the past 20 years, the emerging field of craniofacial tissue engineering has adopted these techniques to enhance regeneration of mineralized tissues, salivary gland, and periodontium and to reduce tumor burden of head and neck squamous cell carcinoma. Studies are currently pursuing research on both biomaterial-mediated gene delivery and more clinically efficacious, although potentially more hazardous, viral methods. Although hundreds of gene therapy clinical trials have taken place in the past 20 years, we must still work to ensure an ideal safety profile for each gene and delivery method combination. With adequate genotoxicity testing, we can expect gene therapy to augment protein delivery strategies and potentially allow for tissue-specific targeting, delivery of multiple signals, and increased spatial and temporal control with the goal of natural tissue replacement in the craniofacial complex.

Drosha regulates hMSCs cell cycle progression through a miRNA independent mechanism

Recently we demonstrated that the miRNA regulate human mesenchymal stem cells (hMSCs) differentiation. To determine the role of the miRNA pathway in hMSCs proliferation, Drosha and Dicer knockdown hMSCs were generated using a lentiviral based tetracycline inducible shRNA. hMSCs with reduced Drosha expression had a significantly reduced proliferation rate, while hMSCs with reduced Dicer expression displayed a proliferation rate similar to untransduced cells. Cell cycle analysis identified that unlike Dicer knockdown, Drosha knockdown hMSCs contained an increased number of G1 phase cells, with a reduced level of cells in S phase, compared to controls. ELISAs of hMSCs revealed decreased levels of pRB and stable levels of total RB with Drosha knockdown. Two key regulators of the G1/S phase transition, cyclin dependent kinase inhibitor 2A (p16) and cyclin dependent kinase inhibitor 2B (p15), were increased in Drosha knockdown cells but not in Dicer knockdown. Transcripts of 28S and 18S rRNA were significantly reduced in Drosha knockdown hMSCs, with no change in rRNA levels in Dicer knockdown hMSCs. 45S pre-rRNA transcripts were not significantly different in either knockdown model. The above results indicate that Drosha modifies hMSCs proliferation through a miRNA independent mechanism, potentially by regulating rRNA processing.

Management of Liver Failure: From Transplantation to Cell-Based Therapy

The severe shortage of deceased donor organs has driven a search for alternative methods of treating liver failure. In this context, cell-based regenerative medicine is emerging as a promising interdisciplinary field of tissue repair and restoration, able to contribute to improving health in a minimally invasive fashion. Several cell types have allowed long-term survival in experimental models of liver injury, but their therapeutic potential in humans should be regarded with deep caution, because few clinical trials are currently available and the number of patients enrolled so far is too small to assess benefits versus risks. This review summarizes the current literature on the physiological role of endogenous stem cells in liver regeneration and on the therapeutic benefits of exogenous stem cell administration with specific emphasis on the potential clinical uses of mesenchymal stem cells. Moreover, critical points that still need clarification, such as the exact identity of the stem-like cell population exerting the beneficial effects, as well as the limitations of stem cell-based therapies, are discussed.

Plasmid-encapsulated polyethylene glycol-grafted polyethylenimine nanoparticles for gene delivery into rat mesenchymal stem cells

Background:

Mesenchymal stem cell transplantation is a promising method in regenerative medicine. Gene-modified mesenchymal stem cells possess superior characteristics of specific tissue differentiation, resistance to apoptosis, and directional migration. Viral vectors have the disadvantages of potential immunogenicity, carcinogenicity, and complicated synthetic procedures. Polyethylene glycol-grafted polyethylenimine (PEG-PEI) holds promise in gene delivery because of easy preparation and potentially targeting modification.

Methods:

A PEG8k-PEI25k graft copolymer was synthesized. Agarose gel retardation assay and dynamic light scattering were used to determine the properties of the nanoparticles. MTT reduction, wound and healing, and differentiation assays were used to test the cytobiological characteristics of rat mesenchymal stem cells, fluorescence microscopy and flow cytometry were used to determine transfection efficiency, and atomic force microscopy was used to evaluate the interaction between PEG-PEI/plasmid nanoparticles and mesenchymal stem cells.

Results:

After incubation with the copolymer, the bionomics of mesenchymal stem cells showed no significant change. The mesenchymal stem cells still maintained high viability, resettled the wound area, and differentiated into adipocytes and osteoblasts. The PEG-PEI completely packed plasmid and condensed plasmid into stable nanoparticles of 100–150 nm diameter. After optimizing the N/P ratio, the PEG-PEI/plasmid microcapsules delivered plasmid into mesenchymal stem cells and obtained an optimum transfection efficiency of 15%–21%, which was higher than for cationic liposomes.

Conclusion:

These data indicate that PEG-PEI is a valid gene delivery agent and has better transfection efficiency than cationic liposomes in mesenchymal stem cells.

Mesenchymal stem cells as therapeutic tools and gene carriers in liver fibrosis and hepatocellular carcinoma

Mesenchymal stem (stromal) cells (MSCs) are a source of circulating progenitors that are able to generate cells of all mesenchymal lineages and to cover cellular demands of injured tissues. The extent of their transdifferentiation plasticity remains controversial. Cells with MSC properties have been obtained from diverse tissues after purification and expansion in vitro. These cellular populations are heterogeneous and under certain conditions show pluripotent-like properties. MSCs present immunosuppressive and anti-inflammatory features and high migratory capacity toward inflamed or remodeling tissues. In this study we review available data regarding factors and signaling axes involved in the chemoattraction and engraftment of MSCs to an injured tissue or to a tissue undergoing active remodeling. Moreover, experimental evidence in support of uses of MSCs as vehicles of therapeutic genes is discussed. Because of its regenerative capacity and its particular immune properties, the liver is a good model to analyze the potential of MSC-based therapies. Finally, the potential application of MSCs and genetically modified MSCs in liver fibrosis and hepatocellular carcinoma (HCC) is proposed in view of available evidence.

Restoration of cellular function of mesenchymal stem cells from a hypophosphatasia patient

Mesenchymal stem cells (MSCs) can differentiate into multiple cell lineages and are used for regenerative treatments for a variety of diseases. However, the patient's cells cannot be used to treat genetic diseases. Allogeneic cells can serve as an alternative but long-term survival is uncertain. Our experience of allo-transplantation to a patient with hypophosphatasia, which is caused by mutations of the tissue non-specific alkaline phosphatase (TNSALP) gene resulting in low serum alkaline phosphatase (ALP) activity and skeletal deformity, did not improve these clinical characteristics. Therefore, we sought to use autologous MSCs for the treatment of hypophosphatasia. MSCs derived from the patient's bone marrow had a similar profile when compared with well-reported MSCs. However, the MSCs had extremely low ALP activity and could not produce a mineralized bone matrix even under the osteogenic culture conditions. We therefore transduced a retroviral vector with TNSALP promoter-driven TNSALP gene in the MSCs. In the culture condition, the MSCs had about 7-fold higher ALP activity than did mock-transduced MSCs, and showed mineralization as well as bone-specific markers. Furthermore, the MSCs, but not mock-transduced MSCs, newly formed bone at the frequency of 50% in nude rats. Transplantation of the TNSALP-transduced autologous MSCs might become a new therapy for hypophosphatasia.

Design and fabrication of 3D porous scaffolds to facilitate cell-based gene therapy

Biomaterials capable of efficient gene delivery by embedded cells provide a fundamental tool for the treatment of acquired or hereditary diseases. A major obstacle is maintaining adequate nutrient and oxygen diffusion to cells within the biomaterial. In this study, we combined the solid free-form fabrication and porogen leaching techniques to fabricate three-dimensional scaffolds, with bimodal pore size distribution, for cell-based gene delivery. The objective of this study was to design micro-/macroporous scaffolds to improve cell viability and drug delivery. Murine bone marrow-derived mesenchymal stromal cells (MSCs) genetically engineered to secrete erythropoietin (EPO) were seeded onto poly-L-lactide (PLLA) scaffolds with different microporosities. Over a period of 2 weeks in culture, an increase in cell proliferation and metabolic activity was observed with increasing scaffold microporosity. The concentration of EPO detected in supernatants also increased with increasing microporosity level. Our study shows that these constructs can promote cell viability and release of therapeutic proteins, and clearly demonstrates their capacity for a dual role as scaffolds for tissue regeneration and as delivery systems for soluble gene products.

Potential implications of cell therapy for osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a brittle-bone disease whose hallmark is bone fragility. Since the disease is genetic, there is currently no available cure. Several pharmacological agents have been tried with not much success, except the recent use of bisphosphonates. Stem cells have been suggested as an alternative OI treatment, but many hurdles remain before this technology can be applied for treating patients with OI. This review summarizes what is known at present regarding the application of stem cells to treat OI using animal models, clinical trials using mesenchymal stem cells to treat patients with OI and the knowledge gained from the clinical trials. Application of gene therapy in combination with stem cells is also discussed. The hurdles to be overcome to bring stem cells close to the clinic and future perspectives are discussed.

The therapeutic applications of multipotential mesenchymal/stromal stem cells in skeletal tissue repair

Four decades after the first isolation and characterization of clonogenic bone marrow stromal cells or mesenchymal stem cells (MSC) in the laboratory of Dr. Alexander Friedenstien, the therapeutic application of their progeny following ex vivo expansion are only now starting to be realized in the clinic. The multipotency, paracrine effects, and immune-modulatory properties of MSC present them as an ideal stem cell candidate for tissue engineering and regenerative medicine. In recent years it has come to light that MSC encompass plasticity that extends beyond the conventional bone, adipose, cartilage, and other skeletal structures, and has expanded to the differentiation of liver, kidney, muscle, skin, neural, and cardiac cell lineages. This review will specifically focus on the skeletal regenerative capacity of bone marrow derived MSC alone or in combination with growth factors, biocompatible scaffolds, and following genetic modification.

Human multipotent stromal cells from bone marrow and microRNA: regulation of differentiation and leukemia inhibitory factor expression

We observed that microRNAs (miRNAs) that regulate differentiation in a variety of simpler systems also regulate differentiation of human multipotent stromal cells (hMSCs) from bone marrow. Differentiation of hMSCs into osteoblasts and adipocytes was inhibited by using lentiviruses expressing shRNAs to decrease expression of Dicer and Drosha, two enzymes that process early transcripts to miRNA. Expression analysis of miRNAs during hMSC differentiation identified 19 miRNAs that were up-regulated during osteogenic differentiation and 20 during adipogenic differentiation, 11 of which were commonly up-regulated in both osteogenic and adipogenic differentiation. In silico models predicted that five of the up-regulated miRNAs targeted leukemia inhibitory factor (LIF) expression. The prediction was confirmed for two of the miRNAs, hsa-mir 199a and hsa-mir346, in that over-expression of the miRNAs decreased LIF secretion by hMSCs. The results demonstrate that differentiation of hMSCs is regulated by miRNAs and that several of these miRNAs target LIF.

Controversial issue: is it safe to employ mesenchymal stem cells in cell-based therapies?

The prospective clinical use of multipotent mesenchymal stromal stem cells (MSC) holds enormous promise for the treatment of a large number of degenerative and age-related diseases. However, the challenges and risks for cell-based therapies are multifaceted. The risks for patients receiving stem cells, which have been expanded in vitro in the presence of xenogenic compounds, can hardly be anticipated and methods for the culture and manipulation of "safe" MSC ex vivo are being investigated. During in vitro expansion, stem cells experience a long replicative history and are thus subject to damage from intracellular and extracellular influences. While murine MSC are prone to cellular transformation in culture, human MSC do not transform. One reason for this striking difference is that during long-term culture, human MSC finally become replicatively senescent. In consequence, this greatly restricts their proliferation and differentiation efficiency. It however also limits the yield of sufficient numbers of cells needed for therapy. Another issue is to eliminate contamination of expanding cells with serum-bound pathogenic agents in order to reduce the risks for infection. A recent technical advancement, which applies human serum platelet lysates as an alternative source for growth factors and essential supplements, allows the unimpaired proliferation of MSC in the absence of animal sera. Here, we present an update regarding cellular senescence of MSC and recent insights concerning potential risks associated with their clinical use.

Changes of the Functional Capacity of Mesenchymal Stem Cells due to Aging or Age-Associated Disease - Implications for Clinical Applications and Donor Recruitment

SUMMARY: In contrast to stem cells of embryonic origin, autologous tissue-specific stem cells are easier to introduce into the clinical practice. In this context, molecular and cellular changes, which alter tissue-specific stem cell properties with age, are of particular interest since elderly patients represent the main target group for cell-based therapies. The clinical use of mesenchymal stem cells is an emerging field, especially because this stem cell type appears to be amenable for the treatment of a large number of diseases, such as non-healing bone defects and fractures, inflammatory relief during arthritis, and the repair of suspensory ligament tears. More than that, mesenchymal stem cells provoke effective immune suppression in the context of graft-versus-host disease. Here, we present a comprehensive overview of the recent findings with special attention to age-related changes of mesenchymal stem cell properties and the consequential impact on tissue regeneration and repair, together with the current perception concerning their therapeutic application potential as well as the challenges associated with their clinical use.

Stromal progenitor cells promote leukocyte migration through production of stromal-derived growth factor 1alpha: a potential mechanism for stromal progenitor cell-mediated enhancement of cellular recruitment to wounds

BACKGROUND/PURPOSE

Stromal progenitor cells (SPC) enhance tissue repair in a variety of injury models. However, the mechanisms by which SPCs facilitate tissue repair remain poorly understood. We hypothesized that SPC-enhanced tissue repair is, in part, because of SPC-mediated recruitment of circulating cells to areas of tissue injury. To test this, we examined the migration of leukocytes in response to SPC in vitro.

METHODS

Leukocyte migration was assessed in response to SPC, SPC + transforming growth factor (TGF)-beta1, or SPC + AMD3100 using a Transwell assay system (Corning, distributed by Fisher Scientific, Pittsburgh, PA). Supernatants were collected from lower chambers and analyzed for leukocyte content, leukocyte viability, and stromal-derived growth factor (SDF)-1alpha concentration.

RESULTS

Stromal progenitor cells increased leukocyte migration compared to media alone (450 +/- 70 vs 112 +/- 17 cells/microL; P < .05). SPC treatment with TGF-beta1 resulted in a 36% increase in leukocyte migration and correlated with an increase in SDF-1alpha production. Treatment with AMD3100 resulted in inhibition of leukocyte migration.

CONCLUSIONS

Stromal progenitor cells promote leukocyte migration, and this appears to be mediated through SDF-1alpha production. The SPC production of SDF-1alpha may be modulated by other cytokines present in the microenvironment during wound healing. Together, these observations provide a potential mechanism by which SPC may augment healing through enhanced recruitment of inflammatory cells and tissue progenitor cells to areas of tissue injury.

Scalable human ES culture for therapeutic use: propagation, differentiation, genetic modification and regulatory issues

Embryonic stem cells unlike most adult stem cell populations can replicate indefinitely while preserving genetic, epigenetic, mitochondrial and functional profiles. ESCs are therefore an excellent candidate cell type for providing a bank of cells for allogenic therapy and for introducing targeted genetic modifications for therapeutic intervention. This ability of prolonged self-renewal of stem cells and the unique advantages that this offers for gene therapy, discovery efforts, cell replacement, personalized medicine and other more direct applications requires the resolution of several important manufacturing, gene targeting and regulatory issues. In this review, we assess some of the advance made in developing scalable culture systems, improvement in vector design and gene insertion technology and the changing regulatory landscape.

Histamine receptor H1 and dermatopontin: new downstream targets of the vitamin D receptor

In this study, we used multipotential MSCs and microarray assays to follow the changing patterns of gene expression as MSCs were differentiated to osteoblasts. We analyzed co-expressed gene groups to identify new targets for known transcription factor VDR during differentiation. The roles of two genes (histamine receptor H1 and dermatopontin) as downstream targets for the VDR were confirmed by gel electromotility shift, siRNA inhibition, and chromatin immunoprecipitation assays.

INTRODUCTION

Osteogenesis is stringently controlled by osteoblast-specific signaling proteins and transcription factors. Mesenchymal stem or multipotential stromal cells from bone marrow (MSCs) have been shown to differentiate into osteoblasts in the presence of vitamin D(3).

MATERIALS AND METHODS

We used MSCs and microarray assays to follow the changing patterns of gene expression as MSCs were differentiated to osteoblasts. The data were analyzed with a previously developed strategy to identify new downstream targets of the vitamin D receptor (VDR), known osteogenesis transcription factor. Hierarchical clustering of the data identified 15 distinct patterns of gene expression. Three genes were selected that expressed in the same time-dependent pattern as osteocalcin, a known target for the VDR: histamine receptor H1 (HRH1), Spondin 2 (SPN), and dermatopontin (DPT). RT-PCR, electromotility shift, siRNA inhibition assays, and chromatin immunoprecipitation assays were used to analyze the role of VDR in activation of DPT and HRH1 during differentiation.

RESULTS AND CONCLUSIONS

RT-PCR assays confirmed that the genes were expressed during differentiation of MSCs. The roles of two genes as downstream targets for the VDR were confirmed by gel electromotility shift and chromatin immunoprecipitation assays that showed the presence of VDR complex binding sequences. Overexpression of VDR in MG-63 osteosarcoma cells induced the expression of HRH1 and DPT. Inhibition studies with siRNA to DPT and HRH1 showed a decrease in MSC differentiation to osteogenic lineage. In addition, osteogenic differentiation of MSCs was inhibited by the HRH1 inhibitor mepyramine but not the HRH2 inhibitor ranitidine. In conclusion, we show that analysis of co-expressed gene groups is a good tool to identify new targets for known transcription factors.

Osteogenesis imperfecta

Osteogenesis imperfecta is a relatively common hereditary connective tissue disorder characterized by bone fragility and fractures. Other frequently affected tissues include tendons, ligaments, skin, sclera, teeth, and middle and inner ear. Molecular studies have demonstrated that most cases result from mutations affecting the genes responsible for the formation of type 1 collagen. The phenotypic presentation varies from mild to lethal. Commonly observed dental abnormalities include dentinogenesis imperfecta and malocclusion. Medical therapies using bisphosphonates have resulted in reduced fracture risk and decreased bone pain. To date, no cases of bisphosphonate-associated osteonecrosis have been reported. With appropriate precautions, the patient with osteogenesis imperfecta can tolerate and benefit from the delivery of necessary dental care to control oral disease, improve function, and improve esthetics.

Cell biology of membrane trafficking in human disease

Understanding the molecular and cellular mechanisms underlying membrane traffic pathways is crucial to the treatment and cure of human disease. Various human diseases caused by changes in cellular homeostasis arise through a single gene mutation(s) resulting in compromised membrane trafficking. Many pathogenic agents such as viruses, bacteria, or parasites have evolved mechanisms to subvert the host cell response to infection, or have hijacked cellular mechanisms to proliferate and ensure pathogen survival. Understanding the consequence of genetic mutations or pathogenic infection on membrane traffic has also enabled greater understanding of the interactions between organisms and the surrounding environment. This review focuses on human genetic defects and molecular mechanisms that underlie eukaryote exocytosis and endocytosis and current and future prospects for alleviation of a variety of human diseases.

Quantitative polymerase chain reaction as a reliable method to determine functional lentiviral titer afterex vivo gene transfer in human mesenchymal stem cells

BACKGROUND

Human mesenchymal stem cells (hMSCs) are a promising target for ex vivo gene therapy and lentiviruses are excellent gene transfer vehicles in hMSCs since they achieve high transduction rates with long-term gene expression. Nevertheless, senescence of hMSCs may limit therapeutic applications due to time-consuming cell selection and viral titration. Here, we describe a fast and reliable method to determine functional lentiviral titer by quantitative polymerase chain reaction (qPCR) after highly efficient ex vivo gene transfer in hMSCs.

METHODS

Lentivirus production was tested with different types of packaging systems. Using p24 ELISA remaining viral particles were detected in the cell culture supernatant. The lentiviral gene transfer efficiency was quantified by FACS analysis. Lentiviral titers were determined by qPCR of expressed transgenes.

RESULTS

Third-generation self-inactivating vectors showed highly efficient gene transfer in hMSCs. No viral antigen was detected in the cell culture supernatant after four media changes, suggesting the absence of infectious particles after 4 days. We observed a linear correlation between virus dilution and level of transgene expression by qPCR analysis, therefore allowing viral titering by quantification of transgene expression. Finally, we demonstrated that transduced hMSCs retained their stem cell character by differentiation towards adipogenic, osteogenic and chondrogenic lineages.

CONCLUSIONS

Quantification of transgene copy numbers by qPCR is a fast and reliable method to determine functional lentiviral titer after ex vivo gene transfer in hMSCs.

A comparison of the effectiveness of cationic polymers poly-L-lysine (PLL) and polyethylenimine (PEI) for non-viral delivery of plasmid DNA to bone marrow stromal cells (BMSC)

Bone marrow stromal cells (BMSC) represent an important cell phenotype for pursuit of successful gene therapy. Non-viral methods to enable expression of exogenous genes in BMSC will accelerate clinical application of gene therapy, without the concerns associated with the viral means of gene transfer. Towards this end, this study investigated the potential of cationic polymers poly-L-lysine (PLL) and branched polyethylenimine (PEI) as gene carriers for modification of BMSC. Both polymers rapidly (approximately 30 min) condensed a 4.2 kb Enhanced Green Fluorescent Protein (pEGFP-N2) plasmid into 100-200 nm particles. PLL and PEI were both readily internalized with BMSC with >80% of BMSC exhibiting polymer uptake by flow cytometric analysis. The relative uptake of PEI, however, was significantly higher as compared to the PLL. The majority of the BMSC (>60%) exhibited nuclear presence of the polymers as analyzed by fluorescent microscopy. Although both polymers were able to deliver the pEGFP-N2 into the cells under microscopic evaluation, only a small fraction of the cells (<10%) displayed nuclear localization of the plasmid. Consistent with better uptake, PEI gave a higher delivery of pEGFP-N2 into the BMSC, which resulted in a more sustained expression of the model gene EGFP in short-term (7-day) culture. We conclude that both PLL and PEI readily displayed cellular uptake, but PEI was more effective in delivering plasmid DNA intracellularly, which was likely the underlying basis for a more sustained gene expression.

Mesenchymal stromal cells

PURPOSE OF REVIEW

Our understanding of the biology and properties of mesenchymal stem cells or multipotent mesenchymal stromal cells has expanded dramatically over the last 3 years and is likely to have an impact on clinical practice in the near future, making a review of this topic both timely and relevant

RECENT FINDINGS

Recommendations regarding nomenclature and the definition of mesenchymal stromal cells have been proposed, a rapidly dividing population within the mesenchymal stromal cell compartment has been better defined and the ability of these cells to exhibit characteristics of cells from a variety of lineages has been extended. The notion that tissue repair with mesenchymal stromal cells is related to transdifferentiation has been re-evaluated and, for the myocardium at least, may be due rather to a paracrine mechanism. The most dramatic developments have been in identifying some of the complex mechanisms underlying the immunosuppressive and nonimmunogenic properties of mesenchymal stromal cells which have important implications for the management of conditions like acute graft-versus-host disease.

SUMMARY

Mesenchymal stromal cells are a biologically important cell population that are able to support hematopoiesis, can differentiate along mesenchymal and nonmesenchymal lineages in vitro, are capable of suppressing alloresponses and appear to be nonimmunogenic. These properties suggest emerging roles for mesenchymal stromal cells in cell therapy.

Labelling of human adipose-derived stem cells for non-invasive in vivo cell tracking

Human adipose-derived stem cells (ASC) can be expanded in an undifferentiated state or differentiated along the osteogenic, chondrogenic, adipogenic, myogenic, endothelial and neurogenic lineage. To test their in vivo and in situ regenerative potential, their fate needs to be traced after application in suitable defect models. Non-invasive imaging systems allow for real time tracking of labelled cells in the living animal. We have evaluated a bioluminescence cell tracking approach to visualise ASC labelled with luciferase in the living animal. Two procedures have been tested to efficiently label human stem cells with a reporter gene (luciferase, green fluorescent protein), namely lipofection with Lipofectamine 2000 and electroporation with a Nucleofector device. With both lipofection and nucleofection protocols, we have reached transfection efficiencies up to 60%. Reporter gene expression was detectable for 3 weeks in vitro and did not interfere with the phenotype and the stem cell properties of the cells. By means of a highly sensitive CCD camera, we were able to achieve real time imaging of cell fate for at least 20 days after application (intravenous, intramuscular, intraperitoneal, subcutaneous) in nude mice. Moreover, we were able to influence cell mobility by choosing different modes of application such as enclosure in fibrin matrix. The optical imaging system with transient transfection is an elegant cell-tracking concept to follow survival and fate of human stem cells in small animals.

Erythropoietin delivery by genetically engineered bone marrow stromal cells for correction of anemia in mice with chronic renal failure

The goal of this research was to develop a strategy to couple stem cell and gene therapy for in vivo delivery of erythropoietin (Epo) for treatment of anemia of ESRD. It was shown previously that autologous bone marrow stromal cells (MSCs) can be genetically engineered to secrete pharmacologic amounts of Epo in normal mice. Therefore, whether anemia in mice with mild to moderate chronic renal failure (CRF) can be improved with Epo gene-modified MSCs (Epo+MSCs) within a subcutaneous implant was examined. A cohort of C57BL/6 mice were rendered anemic by right kidney electrocoagulation and left nephrectomy. In these CRF mice, the hematocrit (Hct) dropped from a prenephrectomy baseline of approximately 55% to 40% after induction of renal failure. MSCs from C57BL/6 donor mice were genetically engineered to secrete murine Epo at a rate of 3 to 4 units of Epo/10(6) cells per 24 h, embedded in a collagen-based matrix, and implanted subcutaneously in anemic CRF mice. It was observed that Hct increased after administration of Epo+MSCs, according to cell dose. Implants of 3 million Epo+MSCs per mouse had no effect on Hct, whereas 10 million led to a supraphysiologic effect. The Hct of CRF mice that received 4.5 or 7.5 million Epo+MSCs rose to a peak 54+/-4.0 or 63+/-5.5%, respectively, at 3 wk after implantation and remained above 48 or 54% for >19 wk. Moreover, mice that had CRF and received Epo+MSCs showed significantly greater swimming exercise capacity. In conclusion, these results demonstrate that subcutaneous implantation of Epo-secreting genetically engineered MSCs can correct anemia that occurs in a murine model of CRF.

Positive selection, relaxation, and acceleration in the evolution of the human and chimp genome

For years evolutionary biologists have been interested in searching for the genetic bases underlying humanness. Recent efforts at a large or a complete genomic scale have been conducted to search for positively selected genes in human and in chimp. However, recently developed methods allowing for a more sensitive and controlled approach in the detection of positive selection can be employed. Here, using 13,198 genes, we have deduced the sets of genes involved in rate acceleration, positive selection, and relaxation of selective constraints in human, in chimp, and in their ancestral lineage since the divergence from murids. Significant deviations from the strict molecular clock were observed in 469 human and in 651 chimp genes. The more stringent branch-site test of positive selection detected 108 human and 577 chimp positively selected genes. An important proportion of the positively selected genes did not show a significant acceleration in rates, and similarly, many of the accelerated genes did not show significant signals of positive selection. Functional differentiation of genes under rate acceleration, positive selection, and relaxation was not statistically significant between human and chimp with the exception of terms related to G-protein coupled receptors and sensory perception. Both of these were over-represented under relaxation in human in relation to chimp. Comparing differences between derived and ancestral lineages, a more conspicuous change in trends seems to have favored positive selection in the human lineage. Since most of the positively selected genes are different under the same functional categories between these species, we suggest that the individual roles of the alternative positively selected genes may be an important factor underlying biological differences between these species.

Since the publication of the human and the chimp genomes, one of the major challenges in evolutionary biology has begun to be deciphered: namely, the search for positively selected genes that have shaped humanness. Arbiza and colleagues undertake a genomic-scale search for the genes that have been positively selected in human, in chimp, and in their common ancestral lineage. They conclude that events of positive selection were six times more frequent in chimp than in human, although they do not group under specific functional classes that have been preferentially selected in either species. However, in the comparisons of the evolutionary trends between the ancestral and the descendant lineages, they found that most of the relative differences in common classes show an abundance of positive selection on the human branch. By differentiating positive selection from a relaxation of selective constraints, both producing analogous footprints in the genome, they demonstrate that many of the genes previously thought to have been positively selected correspond to likely cases of relaxation. Finally, they quantify the bias produced by the use of average rate–based approaches to concentrate cases of adaptive evolution in these species.

Osteogenesis Imperfecta

Osteogenesis imperfecta is a heritable condition characterized by abnormally brittle bones, with an approximate prevalence of 1/20 000 births. Fractures are the main cause of suffering and disability, but owing to the abundance and wide distribution of the defective type I collagen in the body, a variety of symptoms occur. Several types of osteogenesis imperfecta (I-VII) have been described that vary in severity. For many years, therapy consisted of rehabilitation and orthopedic surgery. Presently, pharmacologic therapies aimed at strengthening bone are available, which decrease the pain and fracture rate associated with this condition, and allow more appropriate rehabilitation programs that will hopefully result in a less marked failure to thrive in affected children. In particular, the bisphosphonates, especially pamidronate, have been used for several years. They have been successful in increasing bone mineral density (BMD) and improving bone resistance, leading to a decrease in the fracture rate. Various regimens have been proposed, but it is the therapeutic regimen first used by Glorieux and co-workers in Montreal that has been the most frequently applied.However, as yet there is no definite consensus regarding the indications for therapy, the osteogenesis imperfecta types that are of the greatest concern, the appropriate age at the outset of therapy, and the treatment duration, without yet speaking about the best bisphosphonate regimen for use. The authors have proposed some personal recommendations for the clinical use of bisphosphonates, based on their own experience with the management of patients with this condition; these include the indications for therapy, based on the clinical status, and the treatment duration. These recommendations will certainly not be unanimously endorsed, but they should help to stimulate discussion. Ameliorating BMD is an important step, but will not prevent all fractures because bisphosphonate therapy does not correct the underlying genetic defect. More recently, stem cell replacement therapy in the child or fetus has been proposed as a therapeutic option.All in all, it is possible that, in order to dramatically decrease the fracture rate, combined therapies aimed at both circumventing the consequences of the gene defect using stem cells and reinforcing bone strength with bisphosphonates will have to be considered. Much work is still necessary before recommending these techniques in clinical practice.