Use of lymphoblastoid cell lines to evaluate the hypersensitivity to ultraviolet radiation in Cockayne syndrome

Baseline cell proliferation rates and response to UV differ in lymphoblastoid cell lines derived from healthy individuals of extreme constitution types

Differences in human phenotypes and susceptibility to complex diseases are an outcome of genetic and environmental interactions. This is evident in diseases that progress through a common set of intermediate patho-endophenotypes. Precision medicine aims to delineate molecular players for individualized and early interventions. Functional studies of lymphoblastoid cell line (LCL) model of phenotypically well-characterized healthy individuals can help deconvolute and validate these molecular mechanisms. In this study, LCLs are developed from eight healthy individuals belonging to three extreme constitution types, deep phenotyped on the basis of Ayurveda. LCLs were characterized by karyotyping and immunophenotyping. Growth characteristics and response to UV were studied in these LCLs. Significant differences in cell proliferation rates were observed between the contrasting groups such that one type (Kapha) proliferates significantly slower than the other two (Vata, Pitta). In response to UV, one of the fast growing groups (Vata) shows higher cell death but recovers its numbers due to an inherent higher rates of proliferation. This study reveals that baseline differences in cell proliferation could be a key to understanding the survivability of cells under UV stress. Variability in baseline cellular phenotypes not only explains the cellular basis of different constitution types but can also help set priors during the design of an individualized therapy with DNA damaging agents. This is the first study of its kind that shows variability of intermediate patho-phenotypes among healthy individuals with potential implications in precision medicine.

Chromatin regulation of DNA damage repair and genome integrity in the central nervous system

With the continued extension of lifespan, aging and age-related diseases have become a major medical challenge to our society. Aging is accompanied by changes in multiple systems. Among these, the aging process in the central nervous system is critically important but very poorly understood. Neurons, as post-mitotic cells, are devoid of replicative associated aging processes, such as senescence and telomere shortening. However, because of the inability to self-replenish, neurons have to withstand challenge from numerous stressors over their lifetime. Many of these stressors can lead to damage of the neurons' DNA. When the accumulation of DNA damage exceeds a neuron's capacity for repair, or when there are deficiencies in DNA repair machinery, genome instability can manifest. The increased mutation load associated with genome instability can lead to neuronal dysfunction and ultimately to neuron degeneration. In this review, we first briefly introduce the sources and types of DNA damage and the relevant repair pathways in the nervous system (summarized in Fig. 1). We then discuss the chromatin regulation of these processes and summarize our understanding of the contribution of genomic instability to neurodegenerative diseases.

Molecular cloning and characterization of Saccharomyces cerevisiae RAD28, the yeast homolog of the human Cockayne syndrome A (CSA) gene

Cockayne syndrome patients exhibit severe developmental and neurological abnormalities. Cells derived from these patients are sensitive to killing by UV radiation and do not support the rapid repair of the transcribed strand of transcriptionally active genes observed in cells from normal individuals. We report the cloning of the Saccharomyces cerevisiae homolog of the Cockayne syndrome A (CSA) gene, which we designate as RAD28. A rad28 null mutant does not manifest increased sensitivity to killing by UV or gamma radiation or to methyl methanesulfonate. Additionally, the rate of repair of the transcribed and nontranscribed strands of the yeast RPB2 gene in the rad28 mutant is identical to that observed in wild-type cells following exposure to UV light. As previously shown for rad7 rad26 and rad16 rad26 double mutants, the rad28 null mutant shows slightly enhanced sensitivity to UV light in the presence of mutations in the RAD7 or RAD16 gene. Both rad28 and rad26 null mutants are hypermutable following exposure to UV light.

The Cockayne syndrome group A gene encodes a WD repeat protein that interacts with CSB protein and a subunit of RNA polymerase II TFIIH

The hereditary disease Cockayne syndrome (CS) is characterized by a complex clinical phenotype. CS cells are abnormally sensitive to ultraviolet radiation and are defective in the repair of transcriptionally active genes. The cloned CSB gene encodes a member of a protein family that includes the yeast Snf2 protein, a component of the transcriptional regulator Swi/Snf. We report the cloning of the CSA cDNA, which can encode a WD repeat protein. Mutations in the cDNA have been identified in CS-A cell lines. CSA protein interacts with CSB protein and with p44 protein, a subunit of the human RNA polymerase II transcription factor IIH. These observations suggest that the products of the CSA and CSB genes are involved in transcription.

Ultraviolet-induced mutations in Cockayne syndrome cells are primarily caused by cyclobutane dimer photoproducts while repair of other photoproducts is normal

We compared the contribution to mutagenesis in Cockayne syndrome (CS) cells of the major class of UV photoproducts, the cyclobutane pyrimidine dimer, to that of other DNA photoproducts by using the mutagenesis shuttle vector pZ189. Lymphoblastoid cell lines from the DNA repair-deficient disorders CS and xeroderma pigmentosum (XP) and a normal line were transfected with UV-treated pZ189. Cyclobutane dimers were selectively removed before transfection by photoreactivation (PR), leaving nondimer photoproducts intact. After UV exposure and replication in CS and XP cells, plasmid survival was abnormally reduced and mutation frequency was abnormally elevated. After PR, plasmid survival increased and mutation frequency in CS cells decreased to normal levels but remained abnormal in XP cells. Sequence analysis of > 200 mutant plasmids showed that with CS cells a major mutational hot spot was caused by unrepaired cyclobutane dimers. These data indicate that with both CS and XP cyclobutane dimers are major photoproducts generating reduced plasmid survival and increased mutation frequency. However, unlike XP, CS cells are proficient in repair of nondimer photoproducts. Since XP but not CS patients have a high frequency of UV-induced skin cancers, our data suggest that prevention of UV-induce skin cancers is associated with proficient repair of nondimer photoproducts.

Protein oxidative damage is associated with life expectancy of houseflies

The objective of this study was to test some of the predictions of the oxidative-stress hypothesis of aging, which postulates that aging is causally associated with the molecular damage inflicted by reactive oxygen species. Protein carbonyl content was used as an index of molecular oxidative modifications. The carbonyl content was found to be associated with the physiological age or life expectancy of flies rather than with their chronological age. Exposure of flies to sublethal hyperoxia (100% oxygen) irreversibly enhanced the carbonyl content of the flies and decreased their rate of oxygen consumption. Results of this study indicate that protein carbonyl content may be a biomarker of aging and support the general concept that oxidative stress may be a causal factor in the aging process.

Cockayne syndrome: review of 140 cases

To define diagnostic criteria for Cockayne Syndrome (CS) and to identify in detail the complications of the condition, a comprehensive review of 140 cases of CS was performed. Criteria required for the diagnosis include poor growth and neurologic abnormality; other very common manifestations include sensorineural hearing loss, cataracts, pigmentary retinopathy, cutaneous photosensitivity, and dental caries. The mean age of death in reported cases is 12 3/12 years, though a few affected individuals have lived into their late teens and twenties. Prenatal growth failure, congenital structural eye anomalies, severe neurologic dysfunction from birth, and the presence of cataracts within the first 3 years of life are predictors of severe disease and early death. In contrast with other disorders of chromosome or DNA repair, cancer has never been reported in a classical CS patient, and there appears to be no predisposition to infectious complications. The wide spectrum of symptoms and severity of the disease suggest that biochemical and genetic heterogeneity exist. CS is an uncommon but devastating genetic condition which will be better understood as the biochemical interrelationships between DNA replication and repair, and between growth, homeostasis, and oncogenesis are unraveled.

Abnormal erythemal response and elevated T lymphocyte HRPT mutant frequency in Cockayne's syndrome

In three children with Cockayne's syndrome (CS), skin exposed to ultraviolet radiation responded transiently either with erythematous papules or an exaggerated sunburn-like response, without chronic actinic damage. Irradiation monochromator tests demonstrated an abnormal delay or reduction in the threshold to ultraviolet (UVB) irradiation-induced erythema similar to that of xeroderma pigmentosum (XP). As with XP there was an elevated frequency of mutants resistant to 6-thioguanine in circulating T lymphocytes. The mutant frequency in a single obligate heterozygote was normal. In contrast to XP, in the two CS individuals studied, adaptive cell-mediated immunity and natural killer cell function were normal. Because the risk of skin cancer is very high in XP but not in CS, the normal immune function in CS provides evidence that immune surveillance may be important in UV tumorigenesis.

Insusceptibility of Cockayne syndrome-derived lymphocytes to plasminogen activator-like protease induction by ultraviolet rays and its abolition by interferon

Protease induced by ultraviolet rays (UV) has been extensively investigated in human cells. Plasminogen activator-like protease (PA) activity was induced soon after UV irradiation in peripheral lymphocytes derived from healthy donors. In contrast, UV-irradiated lymphocytes derived from Cockayne syndrome (CS) cases did not show marked protease inducibility. Epstein-Barr (EB) virus-transformed CS lymphoblastoid cells were also characterized by insusceptibility to UV-induction of PA. However, when CS-derived cells were treated with a human interferon (HuIFN) preparation prior to irradiation, induction of PA activity was detected, irrespective of the kind of HuIFN (alpha or gamma). The results indicate the possibility of abnormal PA metabolism in CS-derived cells.

Absence of beta-amyloid immunoreactivity in mesial temporal lobe in Cockayne's syndrome

Cockayne's syndrome is associated with dementia and other physical signs of premature senescence. Death usually occurs in the first or second decade of life. Because previous neuropathologic descriptions have included neurofibrillary tangles and calcific and dystrophic cerebrovascular changes, we examined the mesial temporal lobes of three children with Cockayne's syndrome (confirmed by 254-nm ultraviolet light studies). Immunohistochemistry was used to determine if beta-amyloid immunoreactivity was present in the parenchyma or cerebral blood vessels. Tissues from the mesial temporal lobe of patients with Alzheimer's disease and Down syndrome were used as controls. None of the three temporal lobes from patients with Cockayne's syndrome contained beta-amyloid immunoreactive material in either the parenchyma or vessels; all of the Alzheimer's disease and Down syndrome controls had beta-amyloid immunoreactivity.

Parkinson's disease and Alzheimer's disease: hypersensitivity to X rays in cultured cell lines

Fibroblast and/or lymphoblastoid lines from patients with several inherited primary neuronal degenerations are hypersensitive to DNA-damaging agents. Therefore, lymphoblastoid lines were irradiated from patients with sporadic Parkinson's disease (PD), Alzheimer's disease, and amyotrophic lateral sclerosis. The mean survival values of the eight Parkinson's disease and of the six Alzheimer's disease lines, but not of the five amyotrophic lateral sclerosis lines, were less than that of the 28 normal lines. Our results with Parkinson's disease and Alzheimer's disease cells can be explained by a genetic defect arising as a somatic mutation during embryogenesis, causing defective repair of the X-ray type of DNA damage. Such a DNA repair defect could cause an abnormal accumulation of spontaneously occurring DNA damage in Parkinson's disease and Alzheimer's disease neurons in vivo, resulting in their premature death.

Hypersensitivity to ionizing radiation in cultured cells from Down syndrome patients

Down syndrome is caused by trisomy of chromosome 21 and is comprised of a constellation of abnormalities including neuropathological features that closely resemble those characterizing the neurodegeneration of Alzheimer disease. Because cultured cell lines from patients with Alzheimer disease and other neurodegenerations have a hypersensitivity to the lethal effects of DNA-damaging agents, we studied the response of Down syndrome lymphoblastoid lines to the lethal effects of ionizing and ultraviolet radiation. Lines from the four Down syndrome patients were more sensitive to X-rays than lines from 28 normal donors (P = 10(-4)), while survival of the Down syndrome lines after ultraviolet irradiation was not significantly different from normal. This hypersensitivity to X-rays, which may reflect defective repair of X-ray-induced DNA damage, represents the first abnormality common to cultured cells from both Down syndrome and Alzheimer disease patients.

A sensitive assay for detecting hypersensitivity to ionizing radiation in lymphoblastoid lines from patients with Duchenne muscular dystrophy and primary neuronal degenerations

Hypersensitivity to the lethal effects of DNA-damaging agents is usually demonstrated using the classical colony-forming ability assay with cultured fibroblast lines. Based on the ability of viable cells in lymphoblastoid lines (Epstein-Barr virus-transformed B lymphocytes) to exclude the vital dye trypan blue, we have developed a more rapid survival assay which has been useful in detecting hypersensitivity to ionizing radiation in certain diseases characterized by primary degeneration of excitable tissue. We now present a complete description of this post-X-ray survival assay. We also demonstrate the suitability of both our assay and our method of data analysis for detecting hypersensitivity to ionizing radiation. This demonstration is based on a detailed analysis of assay results with lymphoblastoid lines from 28 normal donors, 3 ataxia telangiectasia (AT) patients, 2 obligate AT heterozygotes, 7 patients with diseases characterized by cellular hypersensitivity to ultraviolet radiation (UV), and 10 Duchenne muscular dystrophy (DMD) patients.