Development of Respiratory Stem Cells and Progenitor Cells

Essential developmental, genomic stability, and tumour suppressor functions of the mouse orthologue of hSSB1/NABP2

Single-stranded DNA binding proteins (SSBs) regulate multiple DNA transactions, including replication, transcription, and repair. We recently identified SSB1 as a novel protein critical for the initiation of ATM signaling and DNA double-strand break repair by homologous recombination. Here we report that germline Ssb1(-/-) embryos die at birth from respiratory failure due to severe rib cage malformation and impaired alveolar development, coupled with additional skeletal defects. Unexpectedly, Ssb1(-/-) fibroblasts did not exhibit defects in Atm signaling or γ-H2ax focus kinetics in response to ionizing radiation (IR), and B-cell specific deletion of Ssb1 did not affect class-switch recombination in vitro. However, conditional deletion of Ssb1 in adult mice led to increased cancer susceptibility with broad tumour spectrum, impaired male fertility with testicular degeneration, and increased radiosensitivity and IR-induced chromosome breaks in vivo. Collectively, these results demonstrate essential roles of Ssb1 in embryogenesis, spermatogenesis, and genome stability in vivo.

Exploring the role of stem cells in cutaneous wound healing

The skin offers a perfect model system for studying the wound healing cascade, which involves a finely tuned interplay between several cell types, pathways and processes. The dysregulation of these factors may lead to wound healing disorders resulting in chronic wounds, as well as abnormal scars such as hypertrophic and keloid scars. As the contribution of stem cells towards tissue regeneration and wound healing is increasingly appreciated, a rising number of stem cell therapies for cutaneous wounds are currently under development, encouraged by emerging preliminary findings in both animal models and human studies. However, we still lack an in-depth understanding of the underlying mechanisms through which stem cells contribute to cutaneous wound healing. The aim of this review is, therefore, to present a critical synthesis of our current understanding of the role of stem cells in normal cutaneous wound healing. In addition to summarizing wound healing principles and related key molecular and cellular players, we discuss the potential participation of different cutaneous stem cell populations in wound healing, and list corresponding stem cells markers. In summary, this review delineates current strategies, future applications, and limitations of stem cell-based or stem cell-targeted therapy in the management of acute and chronic skin wounds.

Stem cells and the natural history of lung cancer: implications for lung cancer screening

Lung cancer is not simply a single disease, but a collection of several phenotypically very diverse and regionally distinct neoplasias. Its natural history is complex and not yet fully understood. Stem cells and the complex interaction with the microenvironment of the tumor and the immune system play an important role in tumor progression and metastasizing capacity. This finding explains why lung cancer does not always follow the multistep carcinogenetic and exponential growth model and why small lesions do not always equate to early-stage disease. Despite the fact that volume doubling times are increasingly used as surrogate markers for the natural history of lung cancer and as estimates for the proportion of overdiagnosed cases, it is only a momentary impression. At baseline screening especially, screen-detected lung cancer cases are preferably detected when they are in the indolent phase of their growth curve (length-biased sampling), from which it can by no means be concluded that they may not progress or metastasize at a later stage. Because the natural history of lung cancer is only partly elucidated, conclusions on the impact of overdiagnosis in lung cancer screening are premature.

Human embryonic stem cells and lung regeneration

Human embryonic stem cells are pluripotent cells derived from the inner cell mass of preimplantation stage embryos. Their unique potential to give rise to all differentiated cell types has generated great interest in stem cell research and the potential that it may have in developmental biology, medicine and pharmacology. The main focus of stem cell research has been on cell therapy for pathological conditions with no current methods of treatment, such as neurodegenerative diseases, cardiac pathology, retinal dysfunction and lung and liver disease. The overall aim is to develop methods of application either of pure cell populations or of whole tissue parts to the diseased organ under investigation. In the field of pulmonary research, studies using human embryonic stem cells have succeeded in generating enriched cultures of type II pneumocytes in vitro. On account of their potential of indefinite proliferation in vitro, embryonic stem cells could be a source of an unlimited supply of cells available for transplantation and for use in gene therapy. Uncovering the ability to generate such cell types will expand our understanding of biological processes to such a degree that disease understanding and management could change dramatically.

Delivering genes to the organ-localized immune system: long-term results of direct intramarrow transduction

We studied the distribution of transgene-expressing cells after direct gene transfer into the bone marrow (BM). Rats received direct injection into the femoral BM of SV(Nef-FLAG), a Tag-deleted recombinant SV40 carrying a marker gene (FLAG epitope). Controls received an unrelated rSV40 or saline. Blood cells (5%) and femoral marrow cells (25%) expressed FLAG throughout. FLAG expression was assessed in different organs at 1, 4 and 16 months. FLAG+ macrophages were seen throughout the body, and were prominent in the spleen. FLAG+ cells were common in pulmonary alveoli. The former included alveolar macrophages and type II pneumocytes. These cells were not detected at 1 month, occasional at 4 months and common at 16 months after intramarrow injection. Rare liver cells were positive for both FLAG and ferritin, indicating that some hepatocytes also expressed this BM-delivered transgene. Control animals were negative. Thus: (a) fixed tissue phagocytes may be accessible to gene delivery by intramarrow transduction of their progenitors; (b) transduced BM-resident cells or their derivatives may migrate to other organs (lungs) and may differentiate into epithelial cells; and (c) intramarrow injection of rSV40s does not detectably transduce parenchymal cells of other organs.

ABC transporters, neural stem cells and neurogenesis – a different perspective

Stem cells intrigue. They have the ability to divide exponentially, recreate the stem cell compartment, as well as create differentiated cells to generate tissues. Therefore, they should be natural candidates to provide a renewable source of cells for transplantation applied in regenerative medicine. Stem cells have the capacity to generate specific tissues or even whole organs like the blood, heart, or bones. A subgroup of stem cells, the neural stem cells (NSCs), is characterized as a self-renewing population that generates neurons and glia of the developing brain. They can be isolated, genetically manipulated and differentiated in vitro and reintroduced into a developing, adult or a pathologically altered central nervous system. NSCs have been considered for use in cell replacement therapies in various neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. Characterization of genes with tightly controlled expression patterns during differentiation represents an approach to understanding the regulation of stem cell commitment. The regulation of stem cell biology by the ATP-binding cassette (ABC) transporters has emerged as an important new field of investigation. As a major focus of stem cell research is in the manipulation of cells to enable differentiation into a targeted cell population; in this review, we discuss recent literatures on ABC transporters and stem cells, and propose an integrated view on the role of the ABC transporters, especially ABCA2, ABCA3, ABCB1 and ABCG2, in NSCs' proliferation, differentiation and regulation, along with comparisons to that in hematopoietic and other stem cells.

Human 8-oxoguanine DNA glycosylase increases resistance to hyperoxic cytotoxicity in lung epithelial cells and involvement with altered MAPK activity

It is unknown whether base excision DNA repair (BER) proteins interact with mitogen-activated protein kinases (MAPK) under oxidation. Here, we explored roles of BER proteins in signaling transduction involving MAPK during hyperoxia. We demonstrated that ERK1/2 phosphorylation in A549 cells was increased in 95% O₂. p38 activity in A549 cells was also increased by exposure to 95% O₂. To evaluate regulatory roles of MAPK, we have transduced A549 cells and primary alveolar epithelial type II cells (AECII) to overexpress 8-oxoguanine DNA glycosylase (hOgg1). Overexpression of hOgg1 reduced hyperoxic toxicity in A549 and AECII cells. Furthermore, protection by BER against hyperoxia appeared to involve an upregulation of ERK1/2 and downregulation of p38. These observations demonstrate, for the first time, that reduction of hyperoxic toxicity by BER proteins may be involved with MAPK activity, thereby impacting cell survival. Furthermore, our studies suggest that modulation of MAPK may be used in combination with BER proteins to counteract hyperoxic toxicity.