3D细胞培养和类器官在骨髓源性间充质干细胞成骨分化中的研究进展

类器官（organoids）来源于自体的组织及干细胞,是通过体外3D培养后形成的细胞团块,这种团块具有原始组织及器官的三维结构,并保留了相对应的功能和遗传特征。由于其具有模拟特定机体器官的发育和疾病发生发展的潜能,这一模型在多种药物的筛选和分子机制研究中拥有更多的优势。近年来,已有实验表明骨髓源性间充质干细胞（BMSCs）通过3D培养及成骨分化可以形成骨的类器官,并可以植入机体发挥特定的作用。这种骨类器官模型的构建,不仅可以为骨质疏松等相关疾病研究提供更多方法,还在骨组织移植及修复等组织工程学中发挥重要作用。本文就BMSCs成骨分化的类器官相关3D模型研究进展作一综述,为BMSCs成骨分化的类器官的基础和临床研究提供更多理论依据和思路。     

Bone marrow derived stem cells in joint and bone diseases: a concise review

Stem cells have huge applications in the field of tissue engineering and regenerative medicine. Their use is currently not restricted to the life-threatening diseases but also extended to disorders involving the structural tissues, which may not jeopardize the patients’ life, but certainly influence their quality of life. In fact, a particularly popular line of research is represented by the regeneration of bone and cartilage tissues to treat various orthopaedic disorders. Most of these pioneering research lines that aim to create new treatments for diseases that currently have limited therapies are still in the bench of the researchers. However, in recent years, several clinical trials have been started with satisfactory and encouraging results. This article aims to review the concept of stem cells and their characterization in terms of site of residence, differentiation potential and therapeutic prospective. In fact, while only the bone marrow was initially considered as a “reservoir” of this cell population, later, adipose tissue and muscle tissue have provided a considerable amount of cells available for multiple differentiation. In reality, recently, the so-called “stem cell niche” was identified as the perivascular space, recognizing these cells as almost ubiquitous. In the field of bone and joint diseases, their potential to differentiate into multiple cell lines makes their application ideally immediate through three main modalities: (1) cells selected by withdrawal from bone marrow, subsequent culture in the laboratory, and ultimately transplant at the site of injury; (2) bone marrow aspirate, concentrated and directly implanted into the injury site; (3) systemic mobilization of stem cells and other bone marrow precursors by the use of growth factors. The use of this cell population in joint and bone disease will be addressed and discussed, analysing both the clinical outcomes but also the basic research background, which has justified their use for the treatment of bone, cartilage and meniscus tissues.     

Can a bone marrow cell contribute to organ regeneration? In vivo analysis using transgenic rats with reporter genes

Although implantation of multipotent bone marrow-derived stem cells represents an attractive new cell therapy to repair damaged tissues, recent reports have raised serious concerns over the feasibility of using stem cells deriving from the bone marrow to promote cell transdifferentiation. We established transgenic (Tg) rats with reporter genes as specific molecular tags to examine the effect of bone marrow cells (BMCs) on transdifferentiation into tissues/organs. To monitor transdifferentiation events of locally transplanted BMCs into hepatocytes or capillary endothelial cells, a liver injury model and an ischemic hind-limb model were developed in rats. To test the ability of circulating bone marrow-derived cells to give rise to myocytes after skeletal muscle injury, we used a bone marrow cell transplantation model from Tg rats, which showed ubiquitous expression of beta-galactosidase (lacZ), into lethally irradiated non-Tg rats. Our results show that there was little transdifferentiation of BMCs into the targeted cells in these tissue injury models. However, in the ischemic hind-limb model, laser Doppler imaging and histologic analysis showed that both implantation of BMCs and treatment with microspheres incorporating basic fibroblast-like growth factor (bFGF), which enables the release of bFGF at the site of action over a period of time, effectively induced angiogenesis. In conclusion, rat BMCs with specific marker genes could be a useful tool for detecting transdifferentiation events in vivo.     

Role of mesenchymal stem cells in bone regeneration and fracture repair: a review

Mesenchymal stem cells (MSCs) are non-haematopoietic stromal stem cells that have many sources, such as bone marrow, periosteum, vessel walls, adipose, muscle, tendon, peripheral circulation, umbilical cord blood, skin and dental tissues. They are capable of self-replication and of differentiating into, and contributing to the regeneration of, mesenchymal tissues, such as bone, cartilage, ligament, tendon, muscle and adipose tissue. The homing of MSCs may play an important role in the repair of bone fractures. As a composite material, the formation and growth of bone tissue is a complex process, including molecular, cell and biochemical metabolic changes. The recruitment of factors with an adequate number of MSCs and the micro-environment around the fracture are effective for fracture repair. Several studies have investigated the functional expression of various chemokine receptors, trophic factors and adhesion molecules in human MSCs. Many external factors affect MSC homing. MSCs have been used as seed cells in building tissue-engineered bone grafts. Scaffolds seeded with MSCs are most often used in tissue engineering and include biotic and abiotic materials. This knowledge provides a platform for the development of novel therapies for bone regeneration with endogenous MSCs.     

Can bone marrow differentiate into renal cells?

A considerable plasticity of adult stem cells has been confirmed in a wide variety of tissues. In particular, the pluripotency of bone marrow-derived stem cells may influence the regeneration of injured tissues and may provide novel avenues in regenerative medicine. Bone marrow contains at least hematopoietic and mesenchymal stem cells, and both can differentiate into a wide range of differentiated cells. Side population (SP) cells, which are originally defined in bone marrow cells by high efflux of DNA-binding dye, seem to be a new class of multipotent stem cells. Irrespective of the approach used to obtain stem cells, the fates of marrow-derived cells following bone marrow transplantation can be traced by labeling donor cells with green fluorescence protein or by identifying donor Y chromosome in female recipients. So far, bone marrow-derived cells have been reported to differentiate into renal cells, including mesangial cells, endothelial cells, podocytes, and tubular cells in the kidney, although controversy exists. Further studies are required to address this issue. Cell therapy will be promising when we learn to control stem cells such as bone marrow-derived stem cells, embryonic stem cells, and resident stem cells in the kidney. Identification of factors that support stem cells or promote their differentiation should provide a relevant step towards cell therapy.     

Prepare cells to repair the heart: mesenchymal stem cells for the treatment of heart failure

Heart failure is one of the most important cardiovascular diseases, with high mortality, and invasive treatment such as mechanical circulatory support and cardiac transplantation is sometimes required for severe heart failure. Therefore, the development of less invasive and more effective therapeutic strategies is desired. Cell therapy is attracting growing interest as a new approach for the treatment of heart failure. As a cell source, various kinds of stem/progenitor cells such as bone marrow cells, endothelial progenitor cells, mesenchymal stem cells (MSC) and cardiac stem cells have been investigated for their efficacy and safety. Especially, bone marrow-derived MSC possess multipotency and can be easily expanded in culture, and are thus an attractive therapeutic tool for heart failure. Recent studies have revealed the underlying mechanisms of MSC in cardiac repair: MSC not only differentiate into specific cell types such as cardiomyocytes and vascular endothelial cells, but also secrete a variety of paracrine angiogenic and cytoprotective factors. It has also been suggested that endogenous MSC as well as exogenously transplanted MSC migrate and participate in cardiac repair. Based on these findings, several clinical trials have just been started to evaluate the safety and efficacy of MSC for the treatment of heart failure.     

Multipotent stromal cells derived from the infrapatellar fat pad of the knee

Tissue engineering approaches for promoting the repair of skeletal tissues have focused on cell-based therapies involving multipotent stromal cells. Recent studies have identified such cells in several tissues in the adult human, including skin, muscle, bone marrow, and subcutaneous fat. This study examined the hypothesis that the infrapatellar fat pad of the adult knee contains progenitor cells that have the ability to differentiate into chondrocytes, osteoblasts, or adipocytes under appropriate culture conditions. Cells isolated from the fat pad stroma had a profile of cell-surface molecules similar but not identical to that of bone marrow-derived mesenchymal stem cells. Using defined culture conditions, fat pad-derived stromal cells were induced to differentiate cells with phenotypic characteristics of: (1) chondrocytes, synthesizing cartilage matrix molecules; (2) adipocytes, producing lipid vacuoles and leptin; or (3) osteoblasts, forming mineralized tissue. The culture conditions also modulated the expression of characteristic gene markers for each lineage. This study supports the hypothesis that multipotent stromal cells are present in many connective tissues in the adult human. Given its location and accessibility, the fat pad may prove to be a potential source of progenitor cells for musculoskeletal tissue engineering.     

Stem cells: a new paradigm in medical therapeutics

Even though the stem cells have been studied for decades, only during the past few years has there been an overwhelming proliferation of publications covering isolation, cultivation and utilization of the body's master cells. This paper attempts to summarize the recent studies in the field of stem cells. A number of studies have reported the existence of multipotent stem cells in the cord, cord blood, placenta, bone marrow, brain, heart, teeth, skin, liver, hair follicles and many other tissues and organs, giving rise to cell types other than their tissue of origin. Increased therapeutic use of stem cells has resulted in scientific methods of collection, testing, processing and storage of these cells, with minimal cell damage and differentiation. Cell expansion, bioreactors and tissue engineering are employed extensively to improve the cell dose and outcome. Stem cell infusion, transplantation and implantation are accepted curative therapies for many malignant and non-malignant conditions. Stem cell therapies also provide alternative solutions for the repair and regeneration of various tissues and organs. There has been a dramatic improvement in the understanding of immunosuppressive properties of stem cells on various immune cell types. Stem cells are found to secrete angiogenic cytokines that increase neovascularization. They bring the promise of curing a disease state as these cells normally regenerate tissues in a healthy organism. Stem cell transplantation, in isolation or in combination with other procedures, has been found to be effective. Stem cell therapy is also seen as a possible alternative for the treatment of different diseases such as juvenile diabetes, amyotrophic lateral sclerosis, cerebral palsy, stroke, spinal cord injury and Parkinson's disease. Regenerative medicine using human stem cells is one of the new and promising fields for treating various intractable diseases and damaged organs.     

The regenerative potential of stem cells in acute renal failure

Adult stem cells have been characterized in several tissues as a subpopulation of cells able to maintain. generate, and replace terminally differentiated cells in response to physiological cell turnover or tissue injury. Little is known regarding the presence of stem cells in the adult kidney but it is documented that under certain conditions, such as the recovery from acute injury, the kidney can regenerate itself by increasing the proliferation of some resident cells. The origin of these cells is largely undefined; they are often considered to derive from resident renal stem or progenitor cells. Whether these immature cells are a subpopulation preserved from the early stage of nephrogenesis is still a matter of investigation and represents an attractive possibility. Moreover, the contribution of bone marrow-derived stem cells to renal cell turnover and regeneration has been suggested. In mice and humans, there is evidence that extrarenal cells of bone marrow origin take part in tubular epithelium regeneration. Injury to a target organ can be sensed by bone marrow stem cells that migrate to the site of damage, undergo differentiation, and promote structural and functional repair. Recent studies have demonstrated that hematopoietic stem cells were mobilized following ischemia/reperfusion and engrafted the kidney to differentiate into tubular epithelium in the areas of damage. The evidence that mesenchymal stem cells, by virtue of their renoprotective property, restore renal tubular structure and also ameliorate renal function during experimental acute renal failure provides opportunities for therapeutic intervention.     

骨髓源性干细胞移植肺再生的研究进展

由于肺组织无再生能力,肺疾病的治疗成为棘手的问题。目前认为骨髓源性干细胞（bone marrow derived stem cell）能定向分化成为肺组织细胞,将骨髓源性干细胞移植入损伤的肺组织,通过诱导剂使其向肺泡上皮细胞分化,从而产生肺泡组织。这是一种很有前途的治疗手段,但目前尚处于研究的初级阶段。现对骨髓干细胞移植在各种肺疾病模型中的应用进行综述。