Current Stem Cell Research & Therapy - Volume 7, Issue 4, 2012

Conditions affecting cartilage through damage or age-related degeneration pose significant challenges to individual patients and their healthcare systems. The disease burden will rise in the future as life expectancy increases. This has resulted in vigorous efforts to develop novel therapies to meet current and future needs. Due to the limited regenerative capacity of cartilage, in vitro tissue engineering techniques have emerged as the favoured technique by which to develop replacements. Tissue engineering is mainly concerned with developing cartilage replacements in the form of chondrocyte suspensions and three-dimensional scaffolds seeded with chondrocytes. One major limiting factor in the development of clinically useful cartilage constructs is our understanding of the process by which cartilage is formed, chondrogenesis. For example, techniques of culturing chondrocytes in vitro have been used for decades, resulting in chondrocytelike cells which produce an extracellular matrix of similar composition to native cartilage, but with inferior physical properties. It has now been realised that one aspect of chondrogenesis which had been ignored was the physical context in which cartilage exists in vivo. This has resulted in the development of bioreactor systems which aim to introduce various physical stresses to engineered cartilage in a controlled environment. This has resulted in some improvements in the quality of tissue engineered cartilage. This is but one example of how the knowledge of chondrogenesis has been translated into research practice. This paper aims to review what is currently known about the process of chondrogenesis and discusses how this knowledge can be applied to tissue engineering.

Chondrogenesis is a vital part of adult life, as cartilage is important not only for articulation of joints but also maintenance functions of the body. Chondrogenesis is a five way process of intricate events controlled by specific genes and cell-cell interactions which has been documented over recent years. This review highlights the current literature regarding the process of endochondral ossification and covers the different level of control at agent level. Due to the proliferative nature of chondrogenesis and using chondrocytes for self renewal and repair, current research involves finding ways in which to improve and replicate expansion of chondrocytes. The review summarises ways in which ex vitro expansion can be manipulated using growth factors, external sources and scaffolds.

Potassium channels play a major role in intracellular homeostasis and regulation of cell volume. Intervertebral disc cells respond to mechanical loading in a complex manner. Mechanical loading may play a role in disc degeneration. Lumbar intervertebral disc samples from 5 patients (average age: 47 years, range: 25-64 years) were used for this study, investigating cells from the nucleus pulposus and the annulus fibrosus duplicate samples to determine RNA expression and protein expression. Analysis of mRNA expression by RT-PCR demonstrated that TREK 1 was expressed by nucleus pulposus (n=5) and annulus fibrosus (n=5) cells. Currently, TREK-1 is the only potassium channel known to be activated by intracellular acidosis, and responds to mechanical and chemical stimuli. Whilst the precise role of potassium channels in cellular homeostasis remains to be determined, TREK-1 may be important to protect disc cells against ischaemic damage, and subsequent disc degeneration, and may also play a role in effecting mechanotransduction. Further research is required to fully elucidate the role of the TREK-1 ion channel in intervertebral disc cells.

Mesenchymal stem cells isolated from amnion/amniotic fluid, umbilical cord blood, placental tissue, umbilical cord vein and the Wharton’s Jelly are promising candidates for musculoskeletal tissue engineering of bone and cartilage tissues. The extracorporeal nature of this source avoids the ethical concerns that plague the isolation of embryonic stem cells. Moreover, the harvesting does not require the invasive and discomfort extraction procedures as well as patient risks that attend adult stem cell isolation. Current preclinical studies support the application of these cell-based therapies for the regeneration of musculoskeletal tissues. We performed a review of the literature to focus on actual knowledge and the future perspectives of the stem cells deriving from umbilical cord and placenta for musculoskeletal tissue engineering.

Mesenchymal stem cells (MSCs) have a great capacity for use in regenerative medicine and other clinical applications. However, one question creating curiosity of their use, is how they are affected by ageing. As we now live within an ageing population, the prevalence of age related disorders is increasing, so it is important to investigate how effectively MSCs from older patients can be expanded and differentiated in vitro before their use in autologous cell transplantation. This paper will look at how ageing effects proliferation potential, differentiation potential and cell surface characterisation of human mesenchymal stem cells.

Cartilage tissue engineering is concerned with developing in vitro cartilage implants that closely match the properties of native cartilage, for eventual implantation to replace damaged cartilage. The three components to cartilage tissue engineering are cell source, such as in vitro expanded autologous chondrocytes or mesenchymal progenitor cells, a scaffold onto which the cells are seeded and a bioreactor which attempts to recreate the in vivo physicochemical conditions in which cartilage develops. Although much progress has been made towards the goal of developing clinically useful cartilage constructs, current constructs have inferior physicochemical properties than native cartilage. One of the reasons for this is the neglect of mechanical forces in cartilage culture. Bioreactors have been defined as devices in which biological or biochemical processes can be re-enacted under controlled conditions e.g. pH, temperature, nutrient supply, O2 tension and waste removal. The purpose of this review is to detail the role of bioreactors in the engineering of cartilage, including a discussion of bioreactor designs, current state of the art and future perspectives.

Fracture healing is a complex physiological process. Local vascularity at the site of the fracture has been established as one of the most important factors influencing the healing process, and lack of vascularity has been implicated in atrophic non unions. Existing research has primarily involved utilising Mesenchymal Stem Cells (MSCs) to augment bone healing but there remains much scope to explore the role of stem cells in the vascularisation process. Endothelial Progenitor Cells (EPCs) and other Endothelial Cellular populations (ECs) could constitute a valid alternative to MSCs. This systematic review is examining the importance of co-implantation of MSCs and EPCs/ECs for bone healing. A literature search was performed using the Cochrane Library, OVID Medline, OVID EMBASE and Google Scholar, searching for combinations of the terms ‘EPCs’, ‘Endothelial progenitor cells’, ‘angiogenesis’, ‘fracture’, ‘bone’ and ‘healing’. Finally 18 articles that fulfilled our criteria were included in this review. ECs could be of value for the treatment of critical size bone defects as they are known to be capable of forming ectopic, vascularised bone. The co-implantation of ECs with MSCs is more intriguing when we take into account the vast array of complex reciprocal interactions between ECs and MSCs.

The term tissue engineering is the technology that combines cells, engineering and biological/synthetic material in order to repair, replace or regenerate biological tissues such as bone, muscle, tendons and cartilage. The major human applications of tissue engineering are: skin, bone, cartilage, corneas, blood vessels, left mainstem bronchus and urinary structures. In this systematic review several criteria were identified as the most desirable characteristics of an ideal scaffold. These state that an ideal scaffolds needs to be biodegradable, possess mechanical strength, be highly porous, biocompatible, non-cytotoxic, non antigentic, stuitable for cell attachment, proliferation and differentiation, flexible and elastic, three dimensional, osteoconductive and support the transport of nutrients and metabolic waste. Subsequently, studies reporting on the various advantages and disadvantages of using collagen based scaffolds in musculoskeletal and cartilage tissue engineering were identified. The purpose of this review is to 1) provide a list of ideal characteristics of a scaffold as identified in the literature 2) identify different types of biological protein-based collagen scaffolds used in musculoskeletal and cartilage tissue engineering 3) assess how many of the criteria each scaffold type meets 4) weigh different scaffolds against each other according to their relative properties and shortcomings. The rationale behind this approach is that the ideal scaffold material has not yet been identified. Hence, this review will define how many of the identified ideal characteristics are fulfilled by natural collagen-based scaffolds and address the shortcomings of its use as found in the literature.

Despite substantial progress that has been made in understanding many aspects regarding biology and pathogenesis of human immunodeficiency virus type 1 (HIV-1), there is currently no vaccine or curative treatment available. HIV-1 continues to be a major global health problem. In this regard, new strategies are required for promoting a complete immune reconstitution and eradicating the virus from the body. The rationale for the use of hematopoietic stem cell (HSC)-based gene therapy against HIV infection is that, after transplantation, genetically modified HSCs carrying anti-HIV transgenes would engraft, divide and differentiate into large numbers of mature myeloid and lymphoid cells that express antiviral genes and thus are protected from HIV invasion or productive replication. HIV-1 attachment to susceptible cells involves binding of gp120 to CD4 receptor and subsequently to a HIV co-receptor, either CCR5 or CXCR4. The pivotal role of CCR5 in HIV-1 acquisition and disease progression has been established by the discovery of a naturally occurring 32-bp deletion in CCR5 (CCR5Δ32) which generates a nonfunctional gene product. Homozygosity for CCR5Δ32 confers profound resistance against HIV infection, and heterozygous mutation that induces a decrease in CCR5 surface expression is associated with lower plasma viral load and delayed progression to acquired immune deficiency syndrome (AIDS). This, together with the fact of R5 dominance during the acute and asymptomatic phase, suggests that CCR5 is an attractive target for HIV gene therapeutics. The present review addresses recent advances of CCR5-targeted HSC gene approaches to treat HIV infection, discusses the future prospects and postulates potential strategies in the field.