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2006 Interview with Dr. Akimov

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STEM CELLS Young Investigator Award Recipients 2006: Q & A

STEM CELLS is proud to feature the co-recipients of the STEM CELLS Young Investigator Award, 2006, as they were interviewed by Editor-in-Chief  Dr. Curt I. Civin.

Dr. Civin asked Dr. Sergey S. Akimov about his research and plans for the future.

 

Sergey S. Akimov, Ph.D.

CIC: First, let me extend my personal congratulations and those of the entire Editorial Board of Stem Cells. There were 48 excellent papers among the applicants for this prize, and at least 10 of them were felt to have moved our field considerably. The judges (members of our Editorial Board) had a very hard time deciding which was the most outstanding paper. Indeed, we finally decided to split the very top prize. So, your work has been seriously judged to be field-leading.

SA: Thank you very much. I would like to express again my appreciation to the Editors and Editorial Board of STEM CELLS for choosing me as a co-recipient of the STEM CELLS Young Investigator Award, 2006. I am proud to be honored with the award, and I believe it is an important achievement in my scientific career. I am also grateful to Dr. Robert Hawley, who supervised this project, and to all my colleagues who participated in the study.

CIC: Please tell me, in language intended for a general scientific audience rather than for our stem cell "niche," what hypothesis you were testing in the research from your paper.

SA: Adult stem cells such as hematopoietic stem cells cannot grow in culture for a long time because of spontaneous differentiation and proliferative senescence, entering into a non-dividing state after a finite number of cell divisions. These processes are regulated by several cell-signaling pathways such as those involving tumor suppressor genes. Proliferative senescence is also induced by the shortening of chromosome ends called telomeres. The integrity of telomeres is maintained by a specific ribonucleoprotein complex referred to as telomerase; the key regulatory component of which is its catalytic subunit, telomerase reverse transcriptase (TERT). Telomerase activity is high in embryonic stem cells; it is also present in adult stem cells but it decreases upon culturing in vitro during their differentiation. We hypothesized that inactivation of tumor suppressor genes and reactivation of telomerase activity by a gene transfer-based approach might allow hematopoietic stem cells in human umbilical cord blood to continue to grow, perhaps generating permanent cell lines. Additionally, because proliferative senescence also provides a barrier to malignant transformation, we hypothesized that artificial expression of certain oncogenes would transform the immortalized cell lines into leukemic cells.

CIC: Give me some background rationale, explaining why this hypothesis was important in stem cell research.

SA: Using human embryonic stem cells (hESCs) in biomedical research is restricted by ethical and technical problems. Cell lines derived from adult stem cells of different human tissue origin could replace hESCs in certain applications. For instance, they could serve as a model to study the molecular mechanisms of symmetric versus asymmetric cell division and differentiation as well as the multistep malignant transformation of human stem/progenitor cells.

CIC: Briefly outline your experimental approach to test your hypothesis.

SA: Our experimental approach was mostly based on a gene delivery technique using lentiviral vectors generated by scientists in Dr. Hawley’s group, on multicolor fluorescence activated cell sorting, and on culture conditions that others had previously demonstrated to transiently support hematopoietic stem cell proliferation.

CIC: Was there a specific methodological technique that was very important in these studies?

SA: Using lentiviral vectors for gene delivery allowed efficient infection of cord blood-derived hematopoietic stem cells. Notably, these vectors are able to carry relatively large genes and can integrate into slowly dividing and non-dividing cells, as exemplified by hematopoietic stem cells. An important aspect of the experimental approach was the multicolor cell sorting that allowed us to simultaneously use vectors with different fluorescent markers. This feature let us conveniently separate transduced cells from non-transduced cells that could produce inhibitory growth factors inducing cell differentiation. CIC: What was the outcome (results) of your experiments?

SA: We attempted to immortalize human cord blood-derived hematopoietic stem/progenitor cells by transduction with lentiviral vectors carrying the human TERT (hTERT) gene and/or the human papillomavirus type 16 E6 and E7 oncogenes. The hTERT gene was incapable of prolonging the lifespan of the cord blood progenitor cells. However, cord blood progenitor cells transduced with E6/E7 alone or in concert with hTERT continued to proliferate, giving rise to permanent cell lines with a myeloerythroid/mast cell progenitor pheno-type. Notably, the resulting cord blood cell lines expressing only E6/E7 were highly aneuploid. By comparison, the cord blood cell lines obtained by coexpression of E6/E7 plus hTERT exhibited near-diploid karyotypes with minimal chromosomal aberrations, concomitant with stabilization of telomere length. These results demonstrated a critical role of telomere integrity in genomic stability. Importantly, the immortalized E6/E7 plus hTERT-expressing cord blood cells were not tumorigenic when injected into nonobese diabetic/severe combined immunodeficient mice but could be converted to a malignant state by ectopic expression of a v-H-ras or BCR-ABL oncogene.

CIC: How do you interpret these results? What does this mean for stem cell biology?

SA: I believe that these findings provide proof-of-principle for approaches that might eventually allow establishment of permanent human hematopoietic stem cell lines. In addition, they provide the basis for systematic investigation of experimental transformation of human hematopoietic stem cells in the context of the cancer stem cell paradigm.

CIC: What hypotheses should the field test now?

SA: As an extension of our studies and results, announced by Shinya Yamanaka of Kyoto University in Japan at the recent ISSCR meeting, concerning the programming of mouse skin cells to resemble ESCs, I suggest that using regulated gene expression systems to introduce multiple genes into various adult stem/progenitor cell populations would help to create cell lines with improved differentiation potential. I also think that our approach can be used to test the cancer stem cell hypothesis in different human malignancies.

CIC: Why did you select the journal Stem Cells for your paper?

SA: We selected your journal because of its reputation as one of the leading journals in the field of stem cell biology, because it is specifically focused on stem cell research, and because of its high impact factor.

CIC: Finally, on a more personal note, tell me a little about you, your education, training. What is your position right now? What would you like to do in the near future? What impact do you expect this award to have on your career aspirations?

SA: I graduated in Biophysics from the Nizhnii Novgorod State University (Russia) in 1993. I earned my Ph.D. degree in Molecular Biology and Cell Biology at the Engelhardt Institute of Molecular Biology, Russian Academy of Sciences in Moscow, Russia in 1997. A few months later, I joined the group of Dr. Alexey Belkin in the Biochemistry Department of the American Red Cross Holland Laboratory in Rockville, Maryland as a Research Fellow. In 2001, I joined the Hematopoiesis Department of Dr. Robert Hawley at the same institution. From July 2004 until recently, I have worked as a Research Scientist in Dr. Hawley’s laboratory at the Department of Anatomy and Cell Biology of George Washington University in Washington, DC. Currently, I am holding a Scientist position at the Transmissible Diseases Department of the American Red Cross Holland Laboratory. I work on creating models—including those involving neural stem cells and hematopoietic cells—to study mammalian prions that may potentially be present in blood and blood-derived products of people who were infected, for instance, with bovine spongiform encephalopathy agents causing "mad cow" disease. Misfolded prion proteins play a key role in the development of neurodegenerative disorders such as Creutzfeldt-Jakob disease and other transmissible spongiform encephalopathies. I believe the Stem Cells Young Investigator Award will greatly help to advance my scientific career. It also reinforces my conviction in the significance of stem cell research, and I gratefully commend the decision of the Editorial Board of Stem Cells and Invitrogen Corporation to establish this award.