Faculty Bibliography

Until recently, stem cells were thought to be endowed with unlimited self-renewal capacity and, thus, assumed exempt from aging. But accumulating evidence over the past decade compellingly argues that a measurable and progressive replicative impairment in the hematopoietic, intestinal, and muscle stem cell activity exists from adulthood to old age, resulting in a decline in stem cell function and rendering stem cell aging as the possible link between cellular aging and organismal aging. By using a previously uncharacterized congenic animal model to study genetic regulation of hematopoietic stem cell aging, we have demonstrated definitively that a locus on murine chromosome 2 regulates hematopoietic stem cell aging. In addition to demonstrating that hematopoietic stem cell aging is regulated by a distinct genetic element, experimental evidence links the response of hematopoietic stem cells to DNA double-strand breaks to cellular aging, suggesting DNA integrity influences stem cell aging.

The currently approved therapies for Alzheimer's disease (AD) in the US are designed to modify the function of specific neurotransmitter systems in the brain. While these palliative treatments can benefit some patients for a period of time, they do not halt the relentless cognitive and behavioral deterioration that characterize this neurodegenerative disorder. Consequently, much current research on AD is directed toward illuminating the disease process itself, particularly the abnormal accumulation of certain proteins in brain: the amyloid-beta protein (Abeta) in senile plaques and cerebral blood vessels, and the tau protein in neurofibrillary tangles. Genetic, biochemical and pathologic evidence now favors a primary role of Abeta aggregation in the Alzheimer proteopathic cascade, and studies in mice indicate that lowering the amount of this protein in brain can be beneficial. Recently, Abeta-immunization therapy has emerged as a particularly promising therapeutic option for treating Alzheimer's disease, but unexpected treatment-related side-effects are an overriding issue. These adverse events were not anticipated from preclinical studies with rodents; hence, more biologically relevant models, such as nonhuman primates, are needed to test the safety and efficacy of novel therapies for Alzheimer's disease

Mammalian telomeres end in single-stranded, G-rich 3' overhangs resulting from both the 'end-replication problem' (the inability of DNA polymerase to replicate the very end of the telomeres) and postreplication processing. Telomeric G-rich overhangs are precisely defined in ciliates; the length and the terminal nucleotides are fixed. Human telomeres have very long overhangs that are heterogeneous in size (35-600 nt), indicating that their processing must differ in some respects from model organisms. We developed telomere-end ligation protocols that allowed us to identify the terminal nucleotides of both the C-rich and the G-rich telomere strands. Up to approximately 80% of the C-rich strands terminate in CCAATC-5', suggesting that after replication a nuclease with high specificity or constrained action acts on the C strand. In contrast, the G-terminal nucleotide was less precise than Tetrahymena and Euplotes but still had a bias that changed as a function of telomerase expression

Tissue function requires coordinated multicellular behavior as a consequence of diverse signals integrated through the tissue microenvironment; importantly, these cell-cell and cell-microenvironment interactions also actively suppress cancer. Ionizing radiation (IR) elicits a well-defined cellular response to DNA damage that mediates the fate of the individual cell, concomitantly with a less well-characterized overarching tissue stress response that coordinates the response of multiple cell types via microenvironment signaling. We have now shown that these programs to reestablish homeostasis intersect via mutual regulation by transforming growth factor beta1 (TGF beta 1), which acts as an extracellular sensor and signal of stress. In this review, the concept that this type of functional integration of cell and tissue stress response programs is essential to cancer suppression will be discussed. Our experiments using IR, and several recent studies that experimentally manipulate stromal TGF beta, show that disruption of microenvironment signaling actively promotes malignant progression. Understanding the dynamic interactions between tissue and cell stress responses will be necessary for an accurate assessment of cancer risk and may also provide targets for prevention

Axonal guidance is influenced by many cues, including polypeptide trophic factors, cytokines, diffusible attractants and repellents and changes in calcium. How these signals are conveyed and integrated is not well defined. Recent data suggest that molecules of the canonical Wnt signaling pathway may have direct actions on axonal growth through neurotrophin signaling. This surprising mechanism is supported by local inactivation of glycogen synthase kinase 3beta (GSK-3beta) by nerve growth factor through the integrin-linked kinase. Inhibition of GSK-3beta provides a positive regulatory signal for the cytoskeleton re-arrangement involved in axon extension. Moreover, microtubule stabilization is stimulated by adenomatous polyposis coli protein, a downstream target of GSK3, in response to neurotrophins. Therefore, components of the Wnt signaling pathway are downstream of trophic factors, providing new insights into cytoskeletal regulatory events during axonal growth

Periprosthetic fracture after total joint replacement predominantly occurs at the stem tip. In this study, the effects of gap size, stem stability and cortical thickness between two press-fit, ipsilateral intramedullary stems on the tensile stresses created in the femur were investigated using finite-element models. The findings were confirmed with strain-gauge tests using a composite Sawbone femur. Gap size did not affect the level of stress on the femur. Cortical thickness had an important effect on stress distribution: peak stresses increased as bone cortical thickness decreased. Irrespective of gap size, the tips of loose stems acted as stress risers particularly with thinner cortices; the tips of well-fixed stems, however, did not

BACKGROUND: The impact of strict enforcement of Section 405 of the New York State Public Health Code to restrict resident work to eighty hours per week and the adoption of a similar policy by the Accreditation Council on Graduate Medical Education in 2002 for orthopaedic residency training have not been evaluated. Adoption of these rules has created accreditation as well as staffing problems and has generated controversy in the surgical training community. The purposes of this study were (1) to evaluate the attitudes of orthopaedic residents and attending surgeons toward the Code 405 work-hour regulations and the effect of those regulations on the perceived quality of residency training, quality of life, and patient care and (2) to quantify the effect of the work-hour restrictions on the actual number of hours worked. METHODS: We administered a thirty-four-question Likert-style questionnaire to forty-eight orthopaedic surgery residents (postgraduate years [PGY]-2 through 5) and a similar twenty-nine-question Likert-style questionnaire to thirty-nine orthopaedic attending surgeons. All questionnaires were collected anonymously and analyzed. Additionally, resident work hours before and after strict enforcement of the Code 405 regulations were obtained from resident time sheets. RESULTS: The average weekly work hours decreased from 89.25 to 74.25 hours for PGY-2 residents and from 86.5 to 73.25 hours for PGY-3 residents, and they increased from 61.5 to 68.5 hours for PGY-4 residents. Residents at all levels felt that they had increased time available for reading. There was general agreement between attending and resident surgeons that their operating experience had been negatively impacted. Senior residents thought that their education had been negatively affected, while junior residents thought that their operating experience in general had been negatively affected. Senior residents and attending surgeons felt that continuity of care had been negatively impacted. All agreed that quality of life for the residents had improved and that residents were more rested. CONCLUSIONS: On the basis of the survey data, the implementation of the new work-hour restrictions was found to result in a decrease in the number of hours worked per week for PGY-2 and PGY-3 residents and in an increase in work hours for PGY-4 residents. This could explain the definite difference between the attitudes expressed by the senior residents and those of the junior residents. Senior residents felt that their education was negatively impacted by the work rules, while junior residents expressed a more neutral view. However, senior residents did not believe that their operative experience was as negatively impacted as did junior residents. Although junior and senior residents and attending surgeons agreed that resident quality of life had improved, we were not able to determine whether this offset the perceived negative impact on education, continuity of care, and operative experience

AutoEM is a software package developed by Zhang et al. [J. Struct. Biol. 1356, 251] for semi-automated acquisition of cryo-electron micrographs from Tecnai series electron microscopes and is used frequently at the lowest level of automation. We report here on the new progress that we have made based on their preliminary work. A fourth low-dose state is created where the system can pre-select all the good holes in a grid square from a single CCD image taken at low magnification, making the system operative at much higher levels of automation. An additional control interface enables the operator to monitor the status of the program and the quality of the data, interact with the program, and direct the execution process according to intermediate results. When data acquisition is in progress, all useful information is automatically saved in certain text files which are easily accessible by a database. More detailed improvements and general advantages are illustrated and discussed. We have started to use the program to perform routine data collection. A number of applications show that the performance of the program is satisfactory and the quality of the micrographs and their power spectra acquired by the program is comparable to those manually collected under the same conditions

To insure an adequate supply of nutrients, omnivores choose among available food sources. This process is exemplified by the well-characterized innate aversion of omnivores to otherwise nutritious foods of imbalanced amino acid content. We report that brain-specific inactivation of GCN2, a ubiquitously expressed protein kinase that phosphorylates translation initiation factor 2 alpha (eIF2alpha) in response to intracellular amino acid deficiency, impairs this aversive response. GCN2 inactivation also diminishes phosphorylated eIF2alpha levels in the mouse anterior piriform cortex following consumption of an imbalanced meal. An ancient intracellular signal transduction pathway responsive to amino acid deficiency thus affects feeding behavior by activating a neuronal circuit that biases consumption against imbalanced food sources.

The mouse homeobox gene Gbx2 is first expressed throughout the posterior region of the embryo during gastrulation, and becomes restricted to rhombomeres 1-3 (r1-3) by embryonic day 8.5 (E8.5). Previous studies have shown that r1-3 do not develop in Gbx2 mutants and that there is an early caudal expansion of the midbrain gene Otx2 to the anterior border of r4. Furthermore, expression of Wnt1 and Fgf8, two crucial components of the isthmic organizer, is no longer segregated to adjacent domains in Gbx2 mutants. In this study, we extend the phenotypic analysis of Gbx2 mutants by showing that Gbx2 is not only required for development of r1-3, but also for normal gene expression in r4-6. To determine whether Gbx2 can alter hindbrain development, we generated Hoxb1-Gbx2 (HG) transgenic mice in which Gbx2 is ectopically expressed in r4. We show that Gbx2 is not sufficient to induce r1-3 development in r4. To test whether an Otx2/Gbx2 interface can induce r1-3 development, we introduced the HG transgene onto a Gbx2-null mutant background and recreated a new Otx2/Gbx2 border in the anterior hindbrain. Development of r3, but not r1 and r2, is rescued in Gbx2-/-; HG embryos. In addition, the normal spatial relationship of Wnt1 and Fgf8 is established at the new Otx2/Gbx2 border, demonstrating that an interaction between Otx2 and Gbx2 is sufficient to produce the normal pattern of Wnt1 and Fgf8 expression. However, the expression domains of Fgf8 and Spry1, a downstream target of Fgf8, are greatly reduced in mid/hindbrain junction area of Gbx2-/-; HG embryos and the posterior midbrain is truncated because of abnormal cell death. Interestingly, we show that increased cell death and a partial loss of the midbrain are associated with increased expression of Fgf8 and Spry1 in Gbx2 conditional mutants that lack Gbx2 in r1 after E9.0. These results together suggest that cell survival in the posterior midbrain is positively or negatively regulated by Fgf8, depending on Fgf8 expression level. Our studies provide new insights into the regulatory interactions that maintain isthmic organizer gene expression and the consequences of altered levels of organizer gene expression on cell survival