Recent advances in the cell biology of aging

Deformability of Heterogeneous Red Blood Cells in Aging and Related Pathologies

Aging is interrelated with changes in red blood cell parameters and functionality. In this article, we focus on red blood cells (RBCs) and provide a review of the known changes associated with the characterization of RBC deformability in aging and related pathologies. The biophysical parameters complement the commonly used biochemical parameters and may contribute to a better understanding of the aging process. The power of the deformability measurement approach is well established in clinical settings. Measuring RBCs' deformability has the advantage of relative simplicity, and it reflects the complex effects developing in erythrocytes during aging. However, aging and related pathological conditions also promote heterogeneity of RBC features and have a certain impact on the variance in erythrocyte cell properties. The possible applications of deformability as an early biophysical biomarker of pathological states are discussed, and modulating PIEZO1 as a therapeutic target is suggested. The changes in RBCs' shape can serve as a proxy for deformability evaluation, leveraging single-cell analysis with imaging flow cytometry and artificial intelligence algorithms. The characterization of biophysical parameters of RBCs is in progress in humans and will provide a better understanding of the complex dynamics of aging.

Abnormal Cholesterol Metabolism and Lysosomal Dysfunction Induce Age-Related Hearing Loss by Inhibiting mTORC1-TFEB-Dependent Autophagy

Cholesterol is a risk factor for age-related hearing loss (ARHL). However, the effect of cholesterol on the organ of Corti during the onset of ARHL is unclear. We established a mouse model for the ARHL group (24 months, n = 12) and a young group (6 months, n = 12). Auditory thresholds were measured in both groups using auditory brainstem response (ABR) at frequencies of 8, 16, and 32 kHz. Subsequently, mice were sacrificed and subjected to histological analyses, including transmission electron microscopy (TEM), H&E, Sudan Black B (SBB), and Filipin staining, as well as biochemical assays such as IHC, enzymatic analysis, and immunoblotting. Additionally, mRNA extracted from both young and aged cochlea underwent RNA sequencing. To identify the mechanism, in vitro studies utilizing HEI-OC1 cells were also performed. RNA sequencing showed a positive correlation with increased expression of genes related to metabolic diseases, cholesterol homeostasis, and target of rapamycin complex 1 (mTORC1) signaling in the ARHL group as compared to the younger group. In addition, ARHL tissues exhibited increased cholesterol and lipofuscin aggregates in the organ of Corti, lateral walls, and spiral ganglion neurons. Autophagic flux was inhibited by the accumulation of damaged lysosomes and autolysosomes. Subsequently, we observed a decrease in the level of transcription factor EB (TFEB) protein, which regulates lysosomal biosynthesis and autophagy, together with increased mTORC1 activity in ARHL tissues. These changes in TFEB and mTORC1 expression were observed in a cholesterol-dependent manner. Treatment of ARHL mice with atorvastatin, a cholesterol synthesis inhibitor, delayed hearing loss by reducing the cholesterol level and maintaining lysosomal function and autophagy by inhibiting mTORC1 and activating TFEB. The above findings were confirmed using stress-induced premature senescent House Ear Institute organ of Corti 1 (HEI-OC1) cells. The findings implicate cholesterol in the pathogenesis of ARHL. We propose that atorvastatin could prevent ARHL by maintaining lysosomal function and autophagy by inhibiting mTORC1 and activating TFEB during the aging process.

Investigating the Role of Leukocyte Telomere Length in Treatment-Resistant Depression and in Response to Electroconvulsive Therapy

Psychiatric disorders seem to be characterized by premature cell senescence. However, controversial results have also been reported. In addition, the relationship between accelerated aging and treatment-resistance has scarcely been investigated. In the current study, we measured leukocyte telomere length (LTL) in 148 patients with treatment-resistant depression (TRD, 125 with major depressive disorder, MDD, and 23 with bipolar disorder, BD) treated with electroconvulsive therapy (ECT) and analyzed whether LTL was associated with different response profiles. We also compared LTL between patients with TRD and 335 non-psychiatric controls. For 107 patients for which genome-wide association data were available, we evaluated whether a significant overlap among genetic variants or genes associated with LTL and with response to ECT could be observed. LTL was negatively correlated with age (Spearman’s correlation coefficient = −0.25, p < 0.0001) and significantly shorter in patients with treatment-resistant MDD (Quade’s F = 35.18, p < 0.0001) or BD (Quade’s F = 20.84, p < 0.0001) compared to controls. Conversely, baseline LTL was not associated with response to ECT or remission. We did not detect any significant overlap between genetic variants or genes associated with LTL and response to ECT. Our results support previous findings suggesting premature cell senescence in patients with severe psychiatric disorders and suggest that LTL could not be a predictive biomarker of response to ECT.

Gene Expression Profiles Reveal Extracellular Matrix and Inflammatory Signaling in Radiation-Induced Premature Differentiation of Human Fibroblast in vitro

Purpose

Fibroblasts are considered to play a major role in the development of fibrotic reaction after radiotherapy and premature radiation-induced differentiation has been proposed as a cellular basis. The purpose was to relate gene expression profiles to radiation-induced phenotypic changes of human skin fibroblasts relevant for radiogenic fibrosis.

Materials and Methods

Exponentially growing or confluent human skin fibroblast strains were irradiated in vitro with 1–3 fractions of 4 Gy X-rays. The differentiated phenotype was detected by cytomorphological scoring and immunofluorescence microscopy. Microarray analysis was performed on Human Genome U133 plus2.0 microarrays (Affymetrix) with JMP Genomics software, and pathway analysis with Reactome R-package. The expression levels and kinetics of selected genes were validated with quantitative real-time PCR (qPCR) and Western blotting.

Results

Irradiation of exponentially growing fibroblast with 1 × 4 Gy resulted in phenotypic differentiation over a 5-day period. This was accompanied by downregulation of cell cycle-related genes and upregulation of collagen and other extracellular matrix (ECM)-related genes. Pathway analysis confirmed inactivation of proliferation and upregulation of ECM- and glycosaminoglycan (GAG)-related pathways. Furthermore, pathways related to inflammatory reactions were upregulated, and potential induction and signaling mechanisms were identified. Fractionated irradiation (3 × 4 Gy) of confluent cultures according to a previously published protocol for predicting the risk of fibrosis after radiotherapy showed similar downregulation but differences in upregulated genes and pathways.

Conclusion

Gene expression profiles after irradiation of exponentially growing cells were related to radiation-induced differentiation and inflammatory reactions, and potential signaling mechanisms. Upregulated pathways by different irradiation protocols may reflect different aspects of the fibrogenic process thus providing a model system for further hypothesis-based studies of radiation-induced fibrogenesis.

Lysosome activity is modulated by multiple longevity pathways and is important for lifespan extension in C. elegans

Lysosomes play important roles in cellular degradation to maintain cell homeostasis. In order to understand whether and how lysosomes alter with age and contribute to lifespan regulation, we characterized multiple properties of lysosomes during the aging process in C. elegans. We uncovered age-dependent alterations in lysosomal morphology, motility, acidity and degradation activity, all of which indicate a decline in lysosome function with age. The age-associated lysosomal changes are suppressed in the long-lived mutants daf-2, eat-2 and isp-1, which extend lifespan by inhibiting insulin/IGF-1 signaling, reducing food intake and impairing mitochondrial function, respectively. We found that 43 lysosome genes exhibit reduced expression with age, including genes encoding subunits of the proton pump V-ATPase and cathepsin proteases. The expression of lysosome genes is upregulated in the long-lived mutants, and this upregulation requires the functions of DAF-16/FOXO and SKN-1/NRF2 transcription factors. Impairing lysosome function affects clearance of aggregate-prone proteins and disrupts lifespan extension in daf-2, eat-2 and isp-1 worms. Our data indicate that lysosome function is modulated by multiple longevity pathways and is important for lifespan extension.

Detecting senescent fate in mesenchymal stem cells: a combined cytofluorimetric and ultrastructural approach

Senescence can impair the therapeutic potential of stem cells. In this study, senescence-associated morphofunctional changes in periosteum-derived progenitor cells (PDPCs) from old and young individuals were investigated by combining cytofluorimetry, immunohistochemistry, and transmission electron microscopy. Cell cycle analysis demonstrated a large number of G0/G1 phase cells in PDPCs from old subjects and a progressive accumulation of G0/G1 cells during passaging in cultures from young subjects. Cytofluorimetry documented significant changes in light scattering parameters and closely correlated with the ultrastructural features, especially changes in mitochondrial shape and autophagy, which are consistent with the mitochondrial-lysosomal axis theory of ageing. The combined morphological, biofunctional, and ultrastructural approach enhanced the flow cytometric study of PDPC ageing. We speculate that impaired autophagy, documented in replicative senescent and old PDPCs, reflect a switch from quiescence to senescence. Its demonstration in a tissue with limited turnover-like the cambium layer of the periosteum, where reversible quiescence is the normal stem cell state throughout life-adds a new piece to the regenerative medicine jigsaw in an ageing society.

Cellular Metabolism and Aging

Metabolic changes are hallmarks of aging and genetic and pharmacologic alterations of relevant pathways can extend life span. In this review, we will outline how cellular biochemistry and energy homeostasis change during aging. We will highlight protein quality control, mitochondria, epigenetics, nutrient-sensing pathways, as well as the interplay between these systems with respect to their impact on cellular health.

P16 INK4a Deletion Ameliorated Renal Tubulointerstitial Injury in a Stress-induced Premature Senescence Model of Bmi-1 Deficiency

To determine whether p16 ^INK4a deletion ameliorated renal tubulointerstitial injury by inhibiting a senescence-associated secretory phenotype (SASP) in Bmi-1-deficient (Bmi-1 ^-/-) mice, renal phenotypes were compared among 5-week-old Bmi-1 and p16 ^INK4a double-knockout, and Bmi-1 ^-/- and wild-type mice. Fifth-passage renal interstitial fibroblasts (RIFs) from the three groups were analyzed for senescence and proliferation. The effect of Bmi-1 deficiency on epithelial-to-mesenchymal transition (EMT) was examined in Bmi-1-knockdown human renal proximal tubular epithelial (HK2) cells, which were treated with concentrated conditioned medium (CM) from the fifth-passage renal interstitial fibroblasts (RIFs) of above three group mice or with exogenous TGF-β1. Our results demonstrated that p16 ^INK4a deletion largely rescued renal aging phenotypes caused by Bmi-1 deficiency, including impaired renal structure and function, decreased proliferation, increased apoptosis, senescence and SASP, DNA damage, NF-κB and TGF-β1/Smad signal activation, inflammatory cell infiltration, and tubulointerstitial fibrosis and tubular atrophy. P16 ^INK4a deletion also promoted proliferation, reduced senescence and SASP of RIFs and subsequently inhibited EMT of Bmi-1-knockdown HK2 cells. TGF-β1 further induced the EMT of Bmi-1-knockdown HK2 cells. Thus, p16 ^INK4a positive senescent cells would be a therapeutic target for preventing renal tubulointerstitial injury.

Biophysical and biomolecular determination of cellular age in humans

Ageing research has focused either on assessing organ- and tissue-based changes, such as lung capacity and cardiac function, or on changes at the molecular scale such as gene expression, epigenetic modifications and metabolism. Here, by using a cohort of 32 samples of primary dermal fibroblasts collected from individuals between 2 and 96 years of age, we show that the degradation of functional cellular biophysical features-including cell mechanics, traction strength, morphology and migratory potential-and associated descriptors of cellular heterogeneity predict cellular age with higher accuracy than conventional biomolecular markers. We also demonstrate the use of high-throughput single-cell technologies, together with a deterministic model based on cellular features, to compute the cellular age of apparently healthy males and females, and to explore these relationships in cells from individuals with Werner syndrome and Hutchinson-Gilford progeria syndrome, two rare genetic conditions that result in phenotypes that show aspects of premature ageing. Our findings suggest that the quantification of cellular age may be used to stratify individuals on the basis of cellular phenotypes and serve as a biological proxy of healthspan.

Endothelial progenitor cells (EPCs) in ageing and age-related diseases: How currently available treatment modalities affect EPC biology, atherosclerosis, and cardiovascular outcomes

Endothelial progenitor cells (EPCs) are mononuclear cells that circulate in the blood and are derived from different tissues, expressing cell surface markers that are similar to mature endothelial cells. The discovery of EPCs has lead to new insights in vascular repair and atherosclerosis and also a new theory for ageing. EPCs from the bone marrow and some other organs aid in vascular repair by migrating to distant vessels where they differentiate into mature endothelial cells and replace old and injured endothelial cells. The ability of EPCs to repair vascular damage depends on their number and functionality. Currently marketed drugs used in a variety of diseases can modulate these characteristics. In this review, the effect of currently available treatment options for cardiovascular and metabolic disorders on EPC biology will be discussed. The various EPC-based therapies that will be discussed include lipid-lowering agents, antihypertensive agents, antidiabetic drugs, phosphodiesteraze inhibitors, hormones, as well as EPC capturing stents.

Tissue formation and tissue engineering through host cell recruitment or a potential injectable cell-based biocomposite with replicative potential: Molecular mechanisms controlling cellular senescence and the involvement of controlled transient telomerase activation therapies

Accumulated data indicate that wound-care products should have a composition equivalent to that of the skin: a combination of particular growth factors and extracellular matrix (ECM) proteins endogenous to the skin, together with viable epithelial cells, fibroblasts, and mesenchymal stem cells (MSCs). Strategies consisting of bioengineered dressings and cell-based products have emerged for widespread clinical use; however, their performance is not optimal because chronic wounds persist as a serious unmet medical need. Telomerase, the ribonucleoprotein complex that adds telomeric repeats to the ends of chromosomes, is responsible for telomere maintenance, and its expression is associated with cell immortalization and, in certain cases, cancerogenesis. Telomerase contains a catalytic subunit, the telomerase reverse transcriptase (hTERT). Introduction of TERT into human cells extends both their lifespan and their telomeres to lengths typical of young cells. The regulation of TERT involves transcriptional and posttranscriptional molecular biology mechanisms. The manipulation, regulation of telomerase is multifactorial in mammalian cells, involving overall telomerase gene expression, post-translational protein-protein interactions, and protein phosphorylation. Reactive oxygen species (ROS) have been implicated in aging, apoptosis, and necrosis of cells in numerous diseases. Upon production of high levels of ROS from exogenous or endogenous generators, the redox balance is perturbed and cells are shifted into a state of oxidative stress, which subsequently leads to modifications of intracellular proteins and membrane lipid peroxidation and to direct DNA damage. When the oxidative stress is severe, survival of the cell is dependent on the repair or replacement of damaged molecules, which can result in induction of apoptosis in the injured with ROS cells. ROS-mediated oxidative stress induces the depletion of hTERT from the nucleus via export through the nuclear pores. Nuclear export is initiated by ROS-induced phosphorylation of tyrosine 707 within hTERT by the Src kinase family. It might be presumed that protection of mitochondria against oxidative stress is an important telomere length-independent function for telomerase in cell survival. Biotechnology companies are focused on development of therapeutic telomerase vaccines, telomerase inhibitors, and telomerase promoter-driven cell killing in oncology, have a telomerase antagonist in late preclinical studies. Anti-aging medicine-oriented groups have intervened on the market with products working on telomerase activation for a broad range of degenerative diseases in which replicative senescence or telomere dysfunction may play an important role. Since oxidative damage has been shown to shorten telomeres in tissue culture models, the adequate topical, transdermal, or systemic administration of antioxidants (such as, patented ocular administration of 1% N-acetylcarnosine lubricant eye drops in the treatment of cataracts) may be beneficial at preserving telomere lengths and delaying the onset or in treatment of disease in susceptible individuals. Therapeutic strategies toward controlled transient activation of telomerase are targeted to cells and replicative potential in cell-based therapies, tissue engineering and regenerative medicine.

The Intricate Interplay between Mechanisms Underlying Aging and Cancer

Age is the major risk factor in the incidence of cancer, a hyperplastic disease associated with aging. Here, we discuss the complex interplay between mechanisms underlying aging and cancer as a reciprocal relationship. This relationship progresses with organismal age, follows the history of cell proliferation and senescence, is driven by common or antagonistic causes underlying aging and cancer in an age-dependent fashion, and is maintained via age-related convergent and divergent mechanisms. We summarize our knowledge of these mechanisms, outline the most important unanswered questions and suggest directions for future research.

The hallmarks of fibroblast ageing

Ageing is influenced by the intrinsic disposition delineating what is maximally possible and extrinsic factors determining how that frame is individually exploited. Intrinsic and extrinsic ageing processes act on the dermis, a post-mitotic skin compartment mainly consisting of extracellular matrix and fibroblasts. Dermal fibroblasts are long-lived cells constantly undergoing damage accumulation and (mal-)adaptation, thus constituting a powerful indicator system for human ageing. Here, we use the systematic of ubiquitous hallmarks of ageing (Lopez-Otin et al., 2013, Cell 153) to categorise the available knowledge regarding dermal fibroblast ageing. We discriminate processes inducible in culture from phenomena apparent in skin biopsies or primary cells from old donors, coming to the following conclusions: (i) Fibroblasts aged in culture exhibit most of the established, ubiquitous hallmarks of ageing. (ii) Not all of these hallmarks have been detected or investigated in fibroblasts aged in situ (in the skin). (iii) Dermal fibroblasts aged in vitro and in vivo exhibit additional features currently not considered ubiquitous hallmarks of ageing. (iv) The ageing process of dermal fibroblasts in their physiological tissue environment has only been partially elucidated, although these cells have been a preferred model of cell ageing in vitro for decades.

Telomeres: unlocking the mystery of cell division and aging

Telomeres are DNA sequences that cap the ends of chromosomes, protecting them from fraying and fusing together during replication. During replication, telomeres lose some of their genetic material but are repaired by the ribonucleoprotein telomerase. Both telomeres and telomerase are linked to cell senescence and apoptosis, and research suggests they play key roles in aging, cancer, hereditary syndromes, and chronic diseases. Several theories of aging are reviewed along with the potential impact of telomerase in developing new treatments.

T cell replicative senescence in human aging

The decline of the immune system appears to be an intractable consequence of aging, leading to increased susceptibility to infections, reduced effectiveness of vaccination and higher incidences of many diseases including osteoporosis and cancer in the elderly. These outcomes can be attributed, at least in part, to a phenomenon known as T cell replicative senescence, a terminal state characterized by dysregulated immune function, loss of the CD28 costimulatory molecule, shortened telomeres and elevated production of proinflammatory cytokines. Senescent CD8 T cells, which accumulate in the elderly, have been shown to frequently bear antigen specificity against cytomegalovirus (CMV), suggesting that this common and persistent infection may drive immune senescence and result in functional and phenotypic changes to the T cell repertoire. Senescent T cells have also been identified in patients with certain cancers, autoimmune diseases and chronic infections, such as HIV. This review discusses the in vivo and in vitro evidence for the contribution of CD8 T cell replicative senescence to a plethora of age-related pathologies and a few possible therapeutic avenues to delay or prevent this differentiative end-state in T cells. The age-associated remodeling of the immune system, through accumulation of senescent T cells has farreaching consequences on the individual and society alike, for the current healthcare system needs to meet the urgent demands of the increasing proportions of the elderly in the US and abroad.

T cell replicative senescence in human aging

The decline of the immune system appears to be an intractable consequence of aging, leading to increased susceptibility to infections, reduced effectiveness of vaccination and higher incidences of many diseases including osteoporosis and cancer in the elderly. These outcomes can be attributed, at least in part, to a phenomenon known as T cell replicative senescence, a terminal state characterized by dysregulated immune function, loss of the CD28 costimulatory molecule, shortened telomeres and elevated production of proinflammatory cytokines. Senescent CD8 T cells, which accumulate in the elderly, have been shown to frequently bear antigen specificity against cytomegalovirus (CMV), suggesting that this common and persistent infection may drive immune senescence and result in functional and phenotypic changes to the T cell repertoire. Senescent T cells have also been identified in patients with certain cancers, autoimmune diseases and chronic infections, such as HIV. This review discusses the in vivo and in vitro evidence for the contribution of CD8 T cell replicative senescence to a plethora of age-related pathologies and a few possible therapeutic avenues to delay or prevent this differentiative end-state in T cells. The age-associated remodeling of the immune system, through accumulation of senescent T cells has farreaching consequences on the individual and society alike, for the current healthcare system needs to meet the urgent demands of the increasing proportions of the elderly in the US and abroad.

Fluorescence-based detection and quantification of features of cellular senescence

Cellular senescence is a spontaneous organismal defense mechanism against tumor progression which is raised upon the activation of oncoproteins or other cellular environmental stresses that must be circumvented for tumorigenesis to occur. It involves growth-arrest state of normal cells after a number of active divisions. There are multiple experimental routes that can drive cells into a state of senescence. Normal somatic cells and cancer cells enter a state of senescence upon overexpression of oncogenic Ras or Raf protein or by imposing certain kinds of stress such as cellular tumor suppressor function. Both flow cytometry and confocal imaging analysis techniques are very useful in quantitative analysis of cellular senescence phenomenon. They allow quantitative estimates of multiple different phenotypes expressed in multiple cell populations simultaneously. Here we review the various types of fluorescence methodologies including confocal imaging and flow cytometry that are frequently utilized to study a variety of senescence. First, we discuss key cell biological changes occurring during senescence and review the current understanding on the mechanisms of these changes with the goal of improving existing protocols and further developing new ones. Next, we list specific senescence phenotypes associated with each cellular trait along with the principles of their assay methods and the significance of the assay outcomes. We conclude by selecting appropriate references that demonstrate a typical example of each method.

A comparative analysis of the cell biology of senescence and aging

Various intracellular organelles, such as lysosomes, mitochondria, nuclei, and cytoskeletons, change during replicative senescence, but the utility of these changes as general markers of senescence and their significance with respect to functional alterations have not been comprehensively reviewed. Furthermore, the relevance of these alterations to cellular and functional changes in aging animals is poorly understood. In this paper, we review the studies that report these senescence-associated changes in various aging cells and their underlying mechanisms. Changes associated with lysosomes and mitochondria are found not only in cells undergoing replicative or induced senescence but also in postmitotic cells isolated from aged organisms. In contrast, other changes occur mainly in cells undergoing in vitro senescence. Comparison of age-related changes and their underlying mechanisms in in vitro senescent cells and aged postmitotic cells would reveal the relevance of replicative senescence to the physiological processes occurring in postmitotic cells as individuals age.

Establishment of a new cell line from lepidopteran epidermis and hormonal regulation on the genes

When an insect molts, old cuticle on the outside of the integument is shed by apolysis and a new cuticle is formed under the old one. This process is completed by the epidermal cells which are controlled by 20-hydroxyecdysone (20E) and juvenile hormone. To understand the molecular mechanisms of integument remolding and hormonal regulation on the gene expression, an epidermal cell line from the 5th instar larval integument of Helicoverpa armigera was established and named HaEpi. The cell line has been cultured continuously for 82 passages beginning on June 30, 2005 until now. Cell doubling time was 64 h. The chromosomes were granular and the chromosome mode was from 70 to 76. Collagenase I was used to detach the cells from the flask bottom. Non-self pathogen AcMNPV induced the cells to apoptosis. The cell line was proved to be an epidermal cell line based on its unique gene expression pattern. It responded to 20E and the non-steroidal ecdysone agonist RH-2485. Its gene expression could be knocked down using RNA interference. Various genes in the cell line were investigated based on their response to 20E. This new cell line represents a platform for investigating the 20E signaling transduction pathway, the immune response mechanism in lepidopteran epidermis and interactions of the genes.

Protective effect of long-term angiotensin II inhibition

Experimental studies indicate that angiotensin II (ANG II) through its type 1 receptor (AT(1)) promotes cardiovascular hypertrophy and fibrosis. Therefore, the aim of this study was to analyze whether chronic long-term inhibition of the renin-angiotensin system (RAS) can prevent most of the deleterious effects due to aging in the cardiovascular system of the normal rat. The main objective was to compare two strategies of ANG II blockade: a converting enzyme inhibitor (CEI) and an AT(1) receptor blocker (AT(1)RB). A control group remained untreated; treatment was initiated 2 wk after weaning. A CEI, enalapril (10 mg.kg(-1).day(-1)), or an AT(1)RB, losartan (30 mg.kg(-1).day(-1)), was used to inhibit the RAS. Systolic blood pressure, body weight, and water and food intake were recorded over the whole experimental period. Heart, aorta, and mesenteric artery weight as well as histological analysis of cardiovascular structure were performed at 6 and 18 mo. Twenty animals in each of the three experimental groups were allowed to die spontaneously. The results demonstrated a significant protective effect on the function and structure of the cardiovascular system in all treated animals. Changes observed at 18 mo of age in the hearts and aortas were quite significant, but each treatment completely abolished this deterioration. The similarity between the results detected with either enalapril or losartan treatment clearly indicates that most of the effects are exerted through AT(1) receptors. An outstanding finding was the significant and similar prolongation of life span in both groups of treated animals compared with untreated control animals.

Presence of human circulating progenitor cells for cancer stromal fibroblasts in the blood of lung cancer patients

Recent animal data have suggested that cancer-induced stroma consists of blood-borne fibroblasts as well as tissue-derived fibroblasts. In this study, mononuclear cells isolated from the pulmonary vein blood of lungs resected from lung cancer patients were cultured to confirm the presence of blood-borne fibroblast. In 34% (16 of 47) of the cases, spindle cells with fibroblast morphology proliferated in a disarrayed fashion and were positive for vimentin and collagen type I but negative for both specific myogenic and endothelial markers. The cDNA profiles of blood-borne fibroblasts, tissue-derived (lung) fibroblasts, human vascular smooth muscle cells (HSMCs), and umbilical vein endothelial cells (HUVECs) were clustered with a hierarchical classification algorithm. The profiles of the blood-borne fibroblasts were clearly isolated from those of the tissue-derived fibroblasts, HSMCs, and HUVECs. When carboxyfluorescein succinyl ester (CFSE)-labeled human mononuclear cells from the blood of lung cancer patients were transferred into nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice engrafted with a human lung cancer xenograft, CFSE-labeled fibroblasts were found around the cancer nests. We investigated the several clinicopathological factors of blood-borne fibroblast-positive patients. The blood-borne fibroblast-positive cases had a significantly larger central fibrotic area in primary lung cancer than in the negative cases (123 +/- 29 vs. 59 +/- 13 mm(2); p = .02). Our results indicated that the blood in the vicinity of human lung cancer contains fibroblast progenitor cells that have the capacity to migrate into the cancer stroma and differentiate into fibroblasts having biological characteristics different from those of tissue-derived fibroblasts. Disclosure of potential conflicts of interest is found at the end of this article.

Assessment of in vitro and in vivo activities in the National Cancer Institute's anticancer screen with respect to chemical structure, target specificity, and mechanism of action

This paper examines two biological models of anticancer activity, cytotoxicity and hollow fiber (HF) activity, for chemotherapeutic agents evaluated as part of the National Cancer Institute's (NCI's) drug screening effort. Our analysis proposes strategies to globally assess compounds tested in the NCI's 60-cell (NCI60) in vitro anticancer screen in terms of structural features, biological activity, target specificity, and mechanism of action by data integration via our self-organizing maps of structural and biological response patterns. We have built statistical models to predict compound potency and HF activity based on physicochemical properties. Our results find that it is the combination of different structural properties that determines a compound's biological activity. A direct correlation is also found between compound potency and specificity, indicating that specific targeting, rather than promiscuous poisoning, gives rise to potency. Finally, we offer a strategy to exploit this relationship for future mining of novel anticancer candidates.

Phenotypic changes of adult porcine mesenchymal stem cells induced by prolonged passaging in culture

The in vitro culture of porcine bone marrow-derived mesenchymal stem cells (MSCs) was used for the investigation of adult stem cell biology. Isolated porcine MSCs possessed the ability to proliferate extensively in an antioxidants-rich medium containing 5% fetal bovine serum (FBS). Greater than 40 serial MSC passages and 100 cell population doublings have been recorded for some MSC batches. Early and late passage MSCs were defined here as those cultures receiving less than 5 trypsin passages and more than 15 trypsin passages, respectively. Consistent with their robust ability to proliferate, both the early and late passage MSCs expressed the cell-cycle promoting enzyme p34cdc2 kinase. Late MSCs, however, exhibited certain features reminiscent of cellular aging such as actin accumulation, reduced substrate adherence, and increased activity of lysosomal acid beta-galactosidase. Early MSCs retained the multipotentiality capable of chondrogenic, osteogenic, and adipogenic differentiation upon induction in vitro. In contrast, late MSCs were only capable of adipogenic differentiation, which was greatly enhanced at the expense of the osteochondrogenic potential. Along with these changes in multipotentiality, late MSCs expressed decreased levels of the bone morphogenic protein (BMP-7) and reduced activity of alkaline phosphatase. Late MSCs also exhibited attenuated synthesis of the hematopoietic cytokines granulocyte colony-stimulating factor (G-CSF), leukemia inhibitory factor (LIF), and stem cell factor (SCF). The long-term porcine MSC culture, thus, provides a model system to study the molecular interplay between multiple MSC differentiation cascades in the context of cellular aging.

Differentiation state of skin fibroblast cultures versus risk of subcutaneous fibrosis after radiotherapy

BACKGROUND AND PURPOSE

There is increasing evidence for patient-to-patient variation in the response of normal tissue to radiotherapy. Recently, it has been suggested that accumulation of functional fibrocytes may be a key step in the development of radiation-induced fibrosis. Therefore, we have examined a possible relationship between the differentiation state of untreated fibroblasts and the risk of radiation-induced subcutaneous fibrosis in individual patients.

MATERIALS AND METHODS

We used skin fibroblast cultures isolated from eight postmastectomy radiotherapy patients whose individual clinical radiosensitivity was assessed by the mean excess risk of fibrosis. Different types of potentially mitotic progenitor fibroblasts (MF) and postmitotic functional fibrocytes (PMF) in the terminal differentiation lineage, MFI --> MFII --> MFIII --> PMF, were scored morphologically in clonal culture. Progression of differentiation was quantified by the ratio L/E of colony-forming late (MFIII and late MFII) and early (MFI and early MFII) progenitors.

RESULTS

We observed a correlation between the ratio L/E and the mean risk of fibrosis (rs = 0.743, P = 0.03), indicating an approximately 10-fold increase in L/E with an increasing risk of fibrosis. This was paralleled by a decreasing trend in the absolute numbers of early progenitor types. By contrast, there was no significant correlation between the plating efficiency and the risk of fibrosis.

CONCLUSIONS

The data suggest that the risk of fibrosis increases with the progression of the differentiation of untreated progenitor fibroblasts, indicating that the progression of fibroblast differentiation may be a co-factor in the development of radiation-induced fibrosis. If this hypothesis is validated, it provides a rationale for a novel predictive test to identify patients with an increased risk of subcutaneous fibrosis.

A proton magnetic resonance spectroscopy study of aging and transformed human fibroblasts

Proton magnetic resonance spectroscopy (1H MRS) has been used to monitor changes occurring during aging and transformation in human lung fibroblasts. Aging was studied in MRC-5 cells from nonsenescent (early passage) to presenescent (late passage) and senescence. Nonsenescent cells infected with SV40 virus (pretransformed) were monitored through crisis and subsequent immortalization. Aging changes were observed with one- and two-dimensional MR spectra. Cholesterol and lipid resonances were significantly increased from nonsenescent cultures to senescence. These changes could be caused by chemical or structural changes in the plasma membrane or in intracellular lipid pools. In contrast, choline levels rose from nonsenescent to presenescent cells but at senescence dropped to that of nonsenescent cells. Increased choline levels are often associated with increased cellular proliferation. After SV40 infection of MRC-5 cells there was an increase of cholesterol and lipid levels that peaked at crisis. Newly immortalized cells exhibited a drop in cholesterol and lipid to nonsenescent cell levels, but these rose again in established immortalized cells. In contrast to presensescent cultures, the levels of choline gradually increased from pretransformed to crisis phase but still continued to rise after immortalization. Thus, 1H MRS illustrates similarities in lipid behavior at senescence and crisis, whereas the choline levels are different.

Effect of 1,25-dihydroxyvitamin D3 on proliferation in senescent IMR-90 human fibroblasts

The response of IMR-90 human fetal lung fibroblasts at high population doubling level (PDL > 42) to 1,25-dihydroxyvitamin D3[1,25(OH)2D3] was investigated to clarify whether some metabolic and molecular parameters of senescent cells are affected by the hormone treatment. Pyruvate kinase, lactate dehydrogenase and glucose-6-phosphate dehydrogenase activity significantly increased after treatment of confluent-phase cells with 10 nM 1,25(OH)2D3 for 24 h. Steroid specificity was established by the failure of 10 nM levels of 25-hydroxyvitamin D3 to affect the enzyme activities, while estradiol-17 beta and progesterone produced a slight increase in glucose-6-phosphate dehydrogenase and lactate dehydrogenase levels, respectively. 1,25(OH)2D3 also affected fibroblast proliferation, protein content/cell and DNA synthesis. The cell number significantly decreased after a 48 h incubation with 1,25(OH)2D3 at various concentrations (0.01-1 nM) when compared with control fibroblasts, while an increase in the protein content/cell was demonstrated. The same experiment, carried out by protracting the incubation with the hormone for 72 h, showed a similar trend, but 10 nM 1,25(OH)2D3 was also able to inhibit cell proliferation and to stimulate protein synthesis. The incorporation of [3H]thymidine into DNA increased after the treatment of high PDL fibroblasts with 0.01-1 nM of hormone for 48 h in comparison with controls.

Increased susceptibility of late passage human diploid fibroblasts to oxidative stress

Three strains of human diploid fibroblasts, TIG-3, TIG-7, and MRC-5, were serially cultivated. The susceptibility of early-passage and late-passage cells at 20-30 and 60-70 population doubling levels, respectively, to hydrogen peroxide, the superoxide radical (exposure to the hypoxanthine-xanthine oxidase system), or linoleic acid hydroperoxide was examined for lactate dehydrogenase release. The susceptibility of late-passage cells to such oxidative stress was considerably enhanced compared with early-passage cells. The concentration of reduced glutathione in late-passage cells was lower by 24-44% on a per-cell-number basis and by 86.0-94.5% on a per-protein-quantity basis than in early-passage cells. In addition, the activity of catalase in late-passage cells was lower by 19-46% compared with early-passage cells. There was, however, no difference between the mRNA levels of catalase in early-passage and late-passage cells. The activities and mRNA levels of copper/zinc superoxide dismutase, manganese superoxide dismutase, and glutathione peroxidase in late-passage cells were all higher than in early-passage cells. These results suggest that late-passage cells are more susceptible to oxidative stress than early-passage cells presumably because of decreases in cellular reduced glutathione concentration and catalase activity, and that their primary defense against oxidative stress is reduced glutathione.

Reduction of unscheduled DNA synthesis and plasminogen activator activity in Hutchinson-Gilford fibroblasts during passaging in vitro: partial correction by interferon-beta

Two fibroblast cell lines (PG3KT and PG1NA) derived from Hutchinson-Gilford syndrome (progeria) cases were characterized, at various population doubling levels (PDL), with respect to the capacity of ultraviolet light (UV, mainly 254 nm wavelength)-induced unscheduled DNA synthesis (UDS) and plasminogen activator-like protease activity (PA). The UDS levels in PG3KT and PG1NA cells at PDL 2-3 were only slightly less than those in normal fibroblasts. With increasing PDL, both progeria cell lines exhibited reduction of the UDS levels and undetectable ones at PDL 9-11. Prompt and transient induction of PA was also detectable at less than PDL 5, whereas it was undectable at higher PDL. However, the levels of UDS and PA induction were increased about 3-7 times after pretreatment with 100 IU/ml human interferon (HuIFN)-beta preparations for more than 24 h prior to UV irradiation, although UDS and PA were undetectable at more than PDL 10. These results suggest that cytokines such as HuIFN-beta transiently compensate for the decreases in UDS and PA inducibility in progeria cells with aging.

A theory that may explain the Hayflick limit--a means to delete one copy of a repeating sequence during each cell cycle in certain human cells such as fibroblasts

A model that may explain the limited division potential of certain cells such as human fibroblasts in culture is presented. The central postulate of this theory is that there exists, prior to certain key exons that code for materials needed for cell division, a unique sequence of specific repeating segments of DNA. One copy of such repeating segments is deleted during each cell cycle in cells that are not protected from such deletion through methylation of their cytosine residues. According to this theory, the means through which such repeated sequences are removed, one per cycle, is through the sequential action of enzymes that act much as bacterial restriction enzymes do--namely to produce scissions in both strands of DNA in areas that correspond to the DNA base sequence recognition specificities of such enzymes. After the first scission early in a replicative cycle, that enzyme becomes inhibited, but the cleavage of the first site exposes the closest site in the repetitive element to the action of a second restriction enzyme after which that enzyme also becomes inhibited. Then repair occurs, regenerating the original first site. Through this sequential activation and inhibition of two different restriction enzymes, only one copy of the repeating sequence is deleted during each cell cycle. In effect, the repeating sequence operates as a precise counter of the numbers of cell doubling that have occurred since the cells involved differentiated during development.

Effect of age on antioxidants and molecular markers of oxidative damage in murine epidermis and dermis

This is the first study of antioxidants and oxidative-damage-related parameters in epidermis and dermis of the skin as a function of age. The four major antioxidant enzymes (catalase, superoxide dismutase, glutathione reductase, and glutathione peroxidase), hydrophilic and lipophilic antioxidants, and lipid hydroperoxides were assayed in both epidermis and dermis of young and old hairless mice. Catalase, superoxide dismutase, and glutathione reductase had similar activity levels in young and old animals. Only glutathione peroxidase from epidermis showed an activity decrease due to age. This decrease became apparent when enzyme activity was expressed per mg of total cellular protein. Hydrophilic and lipophilic antioxidants did not change as a function of age, nor did lipid hydroperoxide levels. Both the absolute level of oxidized glutathione and the ratio of oxidized to reduced glutathione were higher in dermis from old mice. These results suggest that skin aging is not accelerated in old age due to a general decrease in the antioxidant capacity of the tissue. The data are compatible, however, with the idea that continuous damage to skin tissue by free radicals occurs throughout an organism's lifetime because scavenging cannot be 100% efficient.

Genomic damage and its repair in young and aging brain

A brief review of the available information concerning age-related genomic (DNA) damage and its repair, with special reference to brain tissue, is presented. The usefulness of examining the validity of DNA-damage and repair hypothesis of aging in a postmitotic cell like neuron is emphasized. The limited number of reports that exist on brain seem to overwhelmingly support the accumulation of DNA damage with age. However, results regarding the age-dependent decline in DNA-repair capacity are conflicting and divided. The possible reasons for these discrepancies are discussed in light of the gathering evidence, including some human genetic disorders, to indicate how complex is the DNA-repair system in higher animals. It is suggested that assessment of repair potential of neurons with respect to a specific damage in a specific gene might yield more definitive answers about the DNA-repair process and its role in aging.

Age-related changes in collagen gel contraction by cultured human lung fibroblasts resulting in cross-over of contraction curves between young and aged cells

We examined the effects of population doubling levels on collagen gel contraction by human lung fibroblasts (TIG-1). The sizes of gels at day 4 of culture, when the number of cells was the same as the initial number, were smaller with young cells than with aged cells. Therefore, retractive force had decreased with in vitro cellular aging. On the other hand, the lag time until gel contraction began became shorter with aging, resulting in the cross-over of contraction curves of young and aged cells. Morphological changes, such as pseudopodia protrusion, were suppressed in collagen gel. The surrounding collagen fibrils prevented young cells from moving more than aged cells. The weakened omnidirectional interaction with collagen fibrils on the entire surface of aged cells might result in an earlier occurrence of morphological change and, thereby, gel contraction.

Stimulation of DNA synthesis in senescent human cells following incubation with plasma membranes

DNA synthesis and mitosis were increased in mitogen-stimulated senescent WI-38 cells following incubation with plasma membranes prepared from young or senescent WI-38 cells, A431 cells, 3T3 cells, or NR6 cells. The percentage of [3H]thymidine-labeled nuclei in senescent cultures was two- to fivefold greater than that seen in controls in which cells were incubated in the absence of membranes or in the presence of boiled membranes. The effect was trypsin sensitive, suggesting that a protein moiety is necessary for stimulation of DNA synthesis. As the culture age increased, basal levels of DNA synthesis, as well as maximal stimulation of DNA synthesis following incubation with plasma membranes, decreased. These observations are consistent with the hypothesis that different subpopulations exist in senescing cultures and suggest a complex pattern of inhibitory and stimulatory regulation of cell proliferation.

Epidermal growth factor suppresses in vitro senescence in the ability of human umbilical vein endothelial cells to proliferate, but not in the ability to produce prostacyclin

Addition of epidermal growth factor (EGF) to culture medium extended the replicative life span of human umbilical vein endothelial (HUVE) cells in culture. In brief, EGF suppresses the age-related decrease (in vitro senescence) in cell proliferative ability. However, the addition of EGF did not extend the culture period in which prostacyclin (PGI2) is actively produced by the cells. Therefore, EGF does not suppress the age-related decrease (in vitro senescence) in the ability of cultured HUVE cells to produce PGI2. These results suggest that the process of in vitro senescence in the cell proliferative ability is not necessarily correlated with that of in vitro senescence in the ability to produce PGI2.

Characterization of nuclear morphology and nuclear matrices in ageing human fibroblasts

It is believed that the mechanisms for cellular senescence may reside within the genome, however, the changes which occur in the DNA and the surrounding nuclear environment have not been well documented. As the dynamic skeletal framework of the nucleus, the nuclear matrix is poised to play a critical role in the ageing process. The nuclear matrix plays a central role in DNA organization and nuclear structural morphology. The important roles of the nuclear matrix in cell structure and function are demonstrated by its properties of tissue specificity and that it is altered by viral infection, differentiation and carcinogenesis. We therefore undertook a study to investigate the morphologic alterations which occur in ageing nuclei and to determine whether compositional changes in the nuclear matrix occur with age in human skin fibroblasts. We found that as the nucleus increases in size and becomes more round with age, the qualitative pattern of the prominent nuclear matrix proteins does not appear to undergo major changes with age. There do, however, appear to be quantitative alterations in these proteins.

Effects of aging in vitro on intracellular proteolysis in cultured rabbit lens epithelial cells in the presence and absence of serum

Alterations in proteolytic capabilities have been associated with abnormalities in the aged eye lens, but in vivo tests of this hypothesis have been difficult to pursue. To simulate aging, we cultured cells from an 8-yr-old rabbit to early (population-doubling level 20 to 30) and late (population-doubling level greater than 125) passage. Long-lived (t1/2 greater than 10 h) and short-lived (t1/2 less than 10 h) intracellular proteins were labeled with [3H]leucine, and the ability of the cells to mount a proteolytic response to the stress of serum withdrawal was determined. For early passage cells, the average t1/2 of long-lived proteins in the presence and absence of serum was 62 and 39 h, respectively. For late-passage cells, the average t1/2 of long-lived proteins in the presence and absence of serum was 58 and 43 h, respectively. The net increase in intracellular proteolysis in the absence of serum was 59 and 35% for early and late-passage cells, respectively. Thus, in vitro-aged rabbit lens epithelial cells amount only 60% the proteolytic response to serum removal shown in "younger" cells. The enhanced ability of early passage cells to respond to serum removal seems to involve lower homeostatic levels of proteolysis in the presence of serum and greater enhancement of proteolysis in the absence of serum. Less than 2% of the protein is in the pool of short-lived proteins. Rates of proteolysis of short-lived proteins in the presence and absence of serum were indistinguishable. With respect to basal proteolytic rates in the presence of serum and ability to mount a proteolytic response upon serum withdrawal, these rabbit lens epithelial cells are similar to bovine lens epithelial cells and fibroblasts.

Changes in the cell surface of human diploid fibroblasts during cellular aging

The electrophoretic mobility of 13 human diploid cell strains, TIG-1, TIG-2, TIG-3, TIG-7, WI-38, IMR-90, MRC-5, MRC-9, TIG-1H, TIG-1L, TIG-2M, TIG-2B, and TIG-3S, which were established from different tissues of human embryos, was studied at different passages. The net negative surface charge of the cells was characteristic for each cell strain and decreased significantly during the in vitro aging of the cells. The decrease in the net negative charge of the cells correlated well with the decrease in cell density throughout the life span of the cells. A strict linear correlation between the electrophoretic mobility and the number of cells harvested at each passage was obtained for all the human diploid cell strains. Moreover, almost the same linear regression coefficient of the cells was obtained among these cell strains. Therefore, the net negative surface charge of human diploid cell strains could serve as a cell surface marker for in vitro cellular aging.

Isozyme polymorphisms in human diploid cell strains for research on cellular aging

Six human lung diploid cell strains established for the study of in vitro cellular aging (TIG-1, TIG-7, WI-38, IMR-90, MRC-5, MRC-9, and HeLa cells as a control) were studied by cellulose acetate membrane electrophoresis for allozymic differences at 18 enzyme loci. Eight enzyme loci (G6PD, PGM1, PGM3, PepA, PGD, ADA, GLO1, and ME), proved to be informative in establishing unique allozyme genetic signatures for all of the cell strains established from the same species and from the same organ. Changes in the allozyme genetic signatures were not observed throughout the life span of TIG-1 and MRC-9 cells. The allozyme genetic signatures can be used as a quick monitor of cell identification and intraspecific cell contamination.

Changes in enzyme activities in skin fibroblasts derived from persons of various ages

We examined antioxidant enzyme activities (catalase, glutathione peroxidase, and superoxide dismutase) in cultured skin fibroblasts (passage number 2-3) derived from 30 persons of various ages. With increasing ages, catalase activity decreased, glutathione peroxidase activity increased slightly, and superoxide dismutase activity was unchanged. After UVA irradiation (4.8 joule/cm2) of the fibroblasts, only catalase activity decreased by 70%. This suggests that catalase may play an important role in the aging of human skin fibroblasts.

Characterization of the subtypes of cell motility in ageing human skin fibroblasts

Previous studies have noted alterations in cell migration during wound healing with age. Both intracellular and extracellular factors alter cell migration. In an effort to clarify the relationship between ageing and cell motility we have utilized time-lapse videomicroscopy to quantitatively and qualitatively study the various subtypes of cell motility including membrane ruffling, lamellapodal extension and cell translocation of ageing human fibroblasts in culture. We demonstrate a global decline in all types of cell motility of human fibroblasts with increasing donor age. Furthermore, we demonstrate that this decrease in cell motility with ageing is independent of chemotactic gradients.

DNA damage metabolism and aging

As a result of permanent exposure to low levels of various endogenous and exogenous genotoxic agents, large numbers of lesions are continuously induced in the DNA of cells of living organisms. Such lesions could lead to dysfunction of cells and tissues, and they might well be the underlying cause of the age-related reduction of homeostatic capacity and the increased incidence of cancer and other diseases of old age. The rate of damage induction as well as the persistence of the lesions depends on the activity, efficiency and reliability of a wide variety of molecular defense systems. However, a certain degree of imperfection seems to be a general characteristic of most of these defense systems and this could lead to a gradual accumulation of DNA alterations during aging. Even when the original lesions are quickly removed, they can still lead to secondary changes in the DNA, such as DNA-sequence changes and changes in gene expression. This process would be accelerated in case of the occurrence of an age-related decline in the efficiency of these molecular defense systems. This review deals with the present knowledge on the occurrence of 'spontaneous' DNA damage in aging organisms, its potential sources, the influence of preventive and processive cellular defense mechanisms and its consequences in terms of DNA-sequence changes, DNA conformational and configurational changes and changes in gene expression. In general, it can be concluded from the data discussed here that, in spite of a number of discrepancies and conflicting results, an age-related accumulation of DNA alterations occurs at all levels, e.g., chemical structure, DNA-sequence organization and gene expression.

Differential degradation of intracellular proteins in human skin fibroblasts of mitotic and mitomycin-C (MMC)-induced postmitotic differentiation states in vitro

Rates of degradation of short- and long-lived proteins were analysed in homogeneous fibroblast cultures of mitotic or mitomycin C (MMC)-induced postmitotic states. When the highly mitotic MFII type cells--the major cell type of so called "early passage" or "young" fibroblasts--differentiate into MFIII type cells, the last mitotic fibroblast type, and further into MMC-induced postmitotic fibroblasts, the degradation of short-lived proteins increases by a factor of 1.4, resulting in significantly reduced half-lives of these proteins in the postmitotic fibroblasts. From the highly mitotic MFII to the final postmitotic PMFVI-type cells via the intermediates MFIII, PMFIV and PMFV, the half lives (t1/2) of short-lived proteins decrease by a total of 122 min in average, from 362 to 240 min. Degradation of long-lived proteins did not change significantly from cell type MFII to PMFVI. As analysed by two-dimensional (2D)-gel electrophoresis the half-lives of the mitotic and postmitotic cell-type-specific proteins except one, protein PIVa (33 kDa; Pi 5.0), range between 33.2 h and 62.9 h. Protein PIVa, the first protein specific for postmitotic cells, is initially expressed 18 h after the induction of the postmitotic state by mitomycin C (MMC) and has a half-life of approximately 66 min. This may indicate that protein PIVa could function as one possible regulatory factor controlling the postmitotic differentiation state.

Etiology and disease process of benign prostatic hyperplasia

The natural history of benign prostatic hyperplasia (BPH) involves two phases. The first, or pathological phase of BPH, involves two stages, termed microscopic and macroscopic BPH, neither of which produces symptomatic clinical dysuria. Nearly all men throughout the world will eventually develop microscopic BPH if they live long enough. In only about one-half of the men with microscopic BPH, however, will microscopic BPH grow to produce a macroscopic enlargement of the gland (i.e., macroscopic BPH), suggesting that additional factors are required for the progression of microscopic to macroscopic BPH. Several theories have been proposed to explain the etiology of the pathological phase of BPH. The major theories include the hypotheses that pathological BPH is due to 1) a shift in prostatic androgen metabolism that occurs with aging, which leads to an abnormal accumulation of dihydrotestosterone, thus producing the enlarged prostate (i.e., DHT hypothesis), 2) a change in the prostatic stromal-epithelial interact that occurs with aging, which leads to an inductive effect on prostatic growth (i.e., embryonic reawakening theory), or 3) an increase in the total prostatic stem cell number and/or an increase in the clonal expanding of the stem cells into amplifying and transit cells that occurs with aging (i.e., stem cell theory). The second, or clinical phase of BPH, involves the progression of pathologic BPH to clinical BPH in which the patient develops symptomatic dysuria. Only about one-half the men with macroscopic BPH progress to clinical BPH. Although the macroscopic enlargement of the prostate is a necessary condition for the development of clinical BPH, this enlargement is usually not sufficient by itself for the progression of pathologic BPH to clinical BPH. The etiology of the progression of pathological BPH to clinical BPH requires additional factors (e.g., prostatitis, vascular infarct, tensile strength of the glandular capsule, etc.). A successful treatment for clinical BPH, therefore, does not necessarily require either the prevention or elimination of all degrees of pathologic BPH. Instead, what is needed is a therapy to prevent or reverse the progression of pathologic BPH to the clinical disease.

Studies on DNA damage and repair in the mammalian brain

Methods for studying breaks in DNA strands and their repair, originally developed for prokaryotes and cultured cell lines, have been applied to preparations from rat brain. The relative sensitivities of these methods, which include alkaline sucrose density gradient sedimentation, nucleoid sedimentation, and ADP-ribosyltransferase assay, are compared.

In vitro aging of articular chondrocytes identified by analysis of DNA and tubulin content and relationship to cell size and protein content

In vitro senescence of chondrocytes, characterized by a decline in the proliferation rate during late passages, resulted from a rapid growth rate in early subcultures to a complete loss of division after seven to nine passages. One senescent-associated phenotypic change was the apparent increase in the density of cytoplasmic cytoskeletal proteins. We examined the relationship between tubulin content and growth (measured by DNA and total protein contents and cell volume), using flow cytometry, in the assessment of cytoskeleton analysis during in vitro aging. In contrast with previous microscopic observations of tubulin organization, flow cytometry revealed a tubulin content that was modulated as a function of protein content and/or cell volume.

Relationships between the cellular glutathione level and in vitro life span of human diploid fibroblasts

In order to examine the role of cellular glutathione (GSH) in the in vitro aging of human diploid fibroblasts, we studied the effects of manipulated cellular GSH levels on their in vitro life span. An increase in cellular GSH level was produced by the addition of N-acetylcysteine (NAC), a carrier of cysteine across cell membranes, into the culture medium, while a decrease in GSH level was produced by the addition of L-buthionine-(R,S)-sulfoximine (BSO), a specific inhibitor of GSH synthetase. When the cells were serially subcultivated in a medium containing NAC or BSO, their life spans were markedly extended or shortened, respectively, in comparison to the life span of cells grown in a control medium. These results suggest that the cellular GSH level is a determinant of the in vitro life span of human diploid cells.

EGF-dependent phosphorylation of the EGF receptor in plasma membranes isolated from young and senescent WI-38 cells

Tyrosine-specific phosphorylation of the receptor for epidermal growth factor (EGF) in plasma membranes isolated from WI-38 cells is EGF-dependent and occurs to an equivalent extent and on identical tryptic peptides in preparations from cells of various in vitro ages. There is a marked reduction, however, in phosphorylation of receptor molecules from senescent as compared with young WI-38 cells, if enzyme activity is assayed in an immune complex following solubilization of plasma membranes with Nonidet P-40 (NP-40). Differences in the level of receptor phosphorylation in young vs. senescent NP-40 extracts are not resolved by changing the temperature at which the assay is performed, or the length of incubation. Moreover, addition of NP-40 or chloroform-methanol extracts of young cells to assays measuring receptor phosphorylation in senescent cell NP-40 preparations does not augment the senescent enzyme activity. The immunopurified senescent receptor is, however, capable of catalyzing phosphorylation of exogenous substrates. These results indicate that the loss of receptor autophosphorylation in solubilized preparations may result from a differential sensitivity of the senescent cell receptor to the detergent. This finding provides a marker for senescence and suggests subtle changes in protein structure, conformation, or regulation of the EGF receptor in senescent cells.

Histone gene expression remains coupled to DNA synthesis during in vitro cellular senescence

Despite a decrease in the extent to which confluent monolayers of late compared to early passage CF3 human diploid fibroblasts can be stimulated to proliferate, the time course of DNA synthesis onset is similar regardless of the in vitro age of the cells. A parallel and stoichiometric relationship is maintained between the rate of DNA synthesis and the cellular levels of histone mRNA independent of the age of the cell cultures. Furthermore, DNA synthesis and cellular histone mRNA levels decline in a coordinate manner after inhibition of DNA replication by hydroxyurea treatment. These results indicate that while the proliferative activity of human diploid fibroblasts decreases with passage in culture, those cells that retain the ability to proliferate continue to exhibit a tight coupling of DNA replication and histone gene expression.