Jason Comander

Biomechanical activation of vascular endothelium as a determinant of its functional phenotype

One of the striking features of vascular endothelium, the single-cell-thick lining of the cardiovascular system, is its phenotypic plasticity. Various pathophysiologic factors, such as cytokines, growth factors, hormones, and metabolic products, can modulate its functional phenotype in health and disease. In addition to these humoral stimuli, endothelial cells respond to their biomechanical environment, although the functional implications of this biomechanical paradigm of activation have not been fully explored. Here we describe a high-throughput genomic analysis of modulation of gene expression observed in cultured human endothelial cells exposed to two well defined biomechanical stimuli—a steady laminar shear stress and a turbulent shear stress of equivalent spatial and temporal average intensity. Comparison of the transcriptional activity of 11,397 unique genes revealed distinctive patterns of up- and down-regulation associated with each type of stimulus. Cluster analyses of transcriptional profiling data were coupled with other molecular and cell biological techniques to examine whether these global patterns of biomechanical activation are translated into distinct functional phenotypes. Confocal immunofluorescence microscopy of structural and contractile proteins revealed the formation of a complex apical cytoskeleton in response to laminar shear stress. Cell cycle analysis documented different effects of laminar and turbulent shear stresses on cell proliferation. Thus, endothelial cells have the capacity to discriminate among specific biomechanical forces and to translate these input stimuli into distinctive phenotypes. The demonstration that hemodynamically derived stimuli can be strong modulators of endothelial gene expression has important implications for our understanding of the mechanisms of vascular homeostasis and atherogenesis.

Interstitial laser hyperthermia model development for minimally invasive therapy of breast carcinoma.

BACKGROUND This investigation describes the preclinical development of a laser fiberoptic interstitial delivery system for the thermal destruction of small breast cancers. We propose adaptation of this technology to stereotactic mammographic instrumentation currently employed for diagnostic core biopsy to thermally ablate a site of disease with maximal treatment efficacy, minimal observable superficial change, reduced patient trauma, and lowered overall treatment costs. STUDY DESIGN Laser hyperthermia is a clinical modality that seeks to achieve tumor destruction through controlled tissue heating. The advantage of laser-induced hyperthermia over traditionally used heat sources such as ultrasound, microwave, or radiowave radiation lies in the ability to focus heat localization to the specific tumor tissue site. Neodymium:yttrium aluminum garnet (Nd:YAG) laser light transmitted through a fiberoptic cable to a diffusing quartz tip can induce such temperature increases leading to localized tissue destruction. Because breast cancer occurs with greatest frequency in the mature woman whose breast tissue has undergone glandular involution with fatty replacement, this study concentrates on determining the resultant laser energy heat distribution within fat and fibrofatty tissue. This investigation studied the time-temperature responses of ex vivo human breast and porcine fibrofatty tissue, which led to an in vivo subcutaneous porcine model for the practical demonstration of a laser hyperthermia treatment of small volumes of porcine mammary chain tissue. RESULTS Spatial recordings of the resultant temperature fields through time exhibited similar, reproducible thermal profiles in both ex vivo human breast and subcutaneous porcine fat. In vivo laser-produced temperature fields in porcine subcutaneous fat were comparable to those in the ex vivo analyses, and showed a histologically, sharply defined, and controllable volume of necrosis with no injury to adjacent tissues or to overlying skin. CONCLUSIONS Interstitially placed, fiberoptically delivered Nd:YAG laser energy is capable of controlled tissue denaturation to a defined volume for the treatment of small breast cancers. It is hoped that this minimally invasive approach, with further investigation and refinement, may lead to the effective treatment of small, well-defined breast cancers that are commonly diagnosed through stereographic mammography and stereotactic core biopsy. The juxtaposition of such a localized treatment modality with these increasingly used diagnostic tools is of considerable promise.

Mechanosensitive Endothelial Gene Expression Profiles

Abstract: The possibility that hemodynamic forces can act as a “local risk factor” for endothelial dysfunction provides a conceptual framework for the long‐standing observation that the earliest lesions of atherosclerosis develop in a nonrandom pattern, the geometries of which correlate with branch points and other regions of altered blood flow. This has led us to hypothesize that hemodynamic forces, in particular wall shear stresses generated by complex patterns of blood flow, can function as both positive and negative stimuli in atherogenesis via effects on endothelial cell gene expression. To understand how endothelial cells in different regions of the arterial tree acquire both functional and dysfunctional phenotypes due to regional hemodynamics, it was important to begin to delineate, in a comprehensive fashion, the mechanoresponsiveness of endothelial cells. To address this fundamental question, we undertook high‐throughput transcriptional profiling to assess the global patterns of gene expression in cultured endothelial cells exposed to two defined biomechanical stimuli. Analyses of the transcriptional activity of thousands of genes have revealed unique patterns of gene expression associated with certain types of stimuli. These unique gene expression programs and their associated functional phenotypes constitute the strongest evidence to date that vascular endothelial cells can discriminate among different types of biomechanical stimuli. The results of these studies and the working hypotheses inspired by detailed molecular analyses of biomechanically activated vascular endothelium promise to provide new insights into the role of hemodynamics in the pathogenesis of atherosclerosis.

Computational comparison of two draft sequences of the human genome

We are in the enviable position of having two distinct drafts of the human genome sequence. Although gaps, errors, redundancy and incomplete annotation mean that individually each falls short of the ideal, many of these problems can be assessed by comparison. Here we present some comparative analyses of these drafts. We look at a number of features of the sequences, including sequence gaps, continuity, consistency between the two sequences and patterns of DNA-binding protein motifs.

Tauroursodeoxycholic acid (TUDCA) protects photoreceptors from cell death after experimental retinal detachment.

Background Detachment of photoreceptors from the underlying retinal pigment epithelium is seen in various retinal disorders such as retinal detachment and age-related macular degeneration and leads to loss of photoreceptors and vision. Pharmacologic inhibition of photoreceptor cell death may prevent this outcome. This study tests whether systemic administration of tauroursodeoxycholic acid (TUDCA) can protect photoreceptors from cell death after experimental retinal detachment in rodents. Methodology/Principal Findings Retinal detachment was created in rats by subretinal injection of hyaluronic acid. The animals were treated daily with vehicle or TUDCA (500 mg/kg). TUNEL staining was used to evaluate cell death. Photoreceptor loss was evaluated by measuring the relative thickness of the outer nuclear layer (ONL). Macrophage recruitment, oxidative stress, cytokine levels, and caspase levels were also quantified. Three days after detachment, TUDCA decreased the number of TUNEL-positive cells compared to vehicle (651±68/mm2 vs. 1314±68/mm2, P = 0.001) and prevented the reduction of ONL thickness ratio (0.84±0.03 vs. 0.65±0.03, P = 0.002). Similar results were obtained after 5 days of retinal detachment. Macrophage recruitment and expression levels of TNF-a and MCP-1 after retinal detachment were not affected by TUDCA treatment, whereas increases in activity of caspases 3 and 9 as well as carbonyl-protein adducts were almost completely inhibited by TUDCA treatment. Conclusions/Significance Systemic administration of TUDCA preserved photoreceptors after retinal detachment, and was associated with decreased oxidative stress and caspase activity. TUDCA may be used as a novel therapeutic agent for preventing vision loss in diseases that are characterized by photoreceptor detachment.

Diagnostic Testing and Disease Monitoring in Birdshot Chorioretinopathy

Birdshot chorioretinopathy (BSCR) is a rare form of posterior uveitis in which hypopigmented choroidal lesions are scattered throughout the posterior pole. In order to avoid the poor natural history of BSCR, many practitioners would argue that it is critical to diagnose and carefully monitor the often subtle activity of this disease; BSCR can progress insidiously in a white and painless eye, and treatment algorithms based on visual acuity, vitreous inflammation, and retinal vascular leakage of fluorescein alone have been ineffective. This article reviews the various modalities that can be used to diagnose and monitor BSCR, including the clinical and ophthalmoscopic features, diagnostic criteria, electroretinography (ERG- full field, multifocal, and pattern), fluorescein angiography (FA), indocyanine green (ICG) angiography, optical coherence tomography (OCT), fundus autofluorescence (AF), visual fields, HLA A29 testing, and other laboratory testing. HLA-A29 testing can be useful in diagnostically borderline cases, but a positive test is not as useful as one might think in cases where the clinical suspicion for BSCR is low. Out of all the testing modalities, the ERG has been studied most extensively in its relationship to successful treatment. The key parameter is the 30 Hz flicker implicit time, which is abnormal in 70% of patients at baseline. A normal implicit time is correlated with the chance that a patient can be successfully tapered from systemic immunomodulatory therapy without recurrence. Alternatively, some practitioners use ICG angiography or visual field testing for adjunctive monitoring. OCT is used most commonly to follow macular edema. While there is no consensus on how to best monitor disease activity, our institution uses serial ERGs as an adjunct to the normal exam.

Improving the statistical detection of regulated genes from microarray data using intensity-based variance estimation

BackgroundGene microarray technology provides the ability to study the regulation of thousands of genes simultaneously, but its potential is limited without an estimate of the statistical significance of the observed changes in gene expression. Due to the large number of genes being tested and the comparatively small number of array replicates (e.g., N = 3), standard statistical methods such as the Students t-test fail to produce reliable results. Two other statistical approaches commonly used to improve significance estimates are a penalized t-test and a Z-test using intensity-dependent variance estimates.ResultsThe performance of these approaches is compared using a dataset of 23 replicates, and a new implementation of the Z-test is introduced that pools together variance estimates of genes with similar minimum intensity. Significance estimates based on 3 replicate arrays are calculated using each statistical technique, and their accuracy is evaluated by comparing them to a reliable estimate based on the remaining 20 replicates. The reproducibility of each test statistic is evaluated by applying it to multiple, independent sets of 3 replicate arrays. Two implementations of a Z-test using intensity-dependent variance produce more reproducible results than two implementations of a penalized t-test. Furthermore, the minimum intensity-based Z-statistic demonstrates higher accuracy and higher or equal precision than all other statistical techniques tested.ConclusionAn intensity-based variance estimation technique provides one simple, effective approach that can improve p-value estimates for differentially regulated genes derived from replicated microarray datasets. Implementations of the Z-test algorithms are available at http://vessels.bwh.harvard.edu/software/papers/bmcg2004.

Management of Cystoid Macular Edema in Retinitis Pigmentosa

ABSTRACT Retinitis pigmentosa is a genetically heterogeneous disorder with an estimated prevalence of one in 4,000 that is classically characterized by the progressive constriction of peripheral vision and a later deterioration of visual acuity. Central vision can be compromised earlier in disease, however, in the approximately 25% of patients that have cystoid macular edema. This poorly understood problem can thus significantly impair patient quality of life, particularly as available treatments have limited efficacy. We will review clinical features of retinitis pigmentosa-associated cystoid macular edema, potential causative mechanisms, and finally, evidence supporting currently employed therapies with emphasis upon which management strategies require further evidence-based evaluation.

Accommodating intraocular lenses: theory and practice.

Because of the challenges of the current presbyopic intraocular lenses (IOLs) as well as the increased cost to patients, many ophthalmologists do not recommend presbyopic IOLs to their patients. Despite the fact that ciliary muscle is still functional after cataract surgery, most patients undergoing cataract surgery are left with uncorrected presbyopia, which currently has no solution that approaches the elegance or effectiveness of the prepresbyopic crystalline lens and its accommodative system. In practice, many patients, especially the elderly, live with their presbyopia uncorrected other than with bifocal spectacles, impeding the vision that their cataract surgery potentially could have restored. One might argue that if a technique for cataract surgery becomes available that could preserve or even restore accommodation to its original level, it would create the largest improvement in the final visual outcomes of cataract surgery since the invention of the IOL itself. Fortunately, progress toward this ‘‘Holy Grail’’ is currently underway. This review will discuss the advantages of the accommodative approach over other treatments for presbyopia, the types of accommodating lenses that are currently available with their mechanism of action and empirical results, as well as discussing the many evolving technologies for restoring accommodation. There are currently 5 fundamental approaches to treating presbyopia: spectacles, monovision, multifocal approaches, surgery on the

Course of Ocular Function in PRPF31 Retinitis Pigmentosa

ABSTRACT Mutations in pre-mRNA splicing factors are the second most common cause of autosomal dominant retinitis pigmentosa, and a major cause of vision loss. The development of gene augmentation therapy for disease caused by mutations in PRPF31 necessitates defining pretreatment characteristics and disease progression of patients with PRPF31-related retinitis pigmentosa. We show rates of decline of visual field area −6.9% per year and 30-Hz flicker cone response of −9.2% per year, which are both similar to observed rates for retinitis pigmentosa. We hypothesize that RNA splicing factor retinitis pigmentosa will be amenable to treatment by AAV-mediated gene therapy, and that understanding the clinical progression rates of PRPF31 retinitis pigmentosa will help with the design of gene therapy clinical trials.