Statin, a nonproliferation-specific protein, is associated with the nuclear envelope and is heterogeneously distributed in cells leaving quiescent state

Probing the mechanism for hydrogel-based stasis induction in human pluripotent stem cells: is the chemical functionality of the hydrogel important?

It is well-known that pluripotent human embryonic stem cells (hPSC) can differentiate into any cell type. Recently, we reported that hPSC colonies enter stasis when immersed in an extremely soft hydrogel comprising hydroxyl-functional block copolymer worms (I. Canton, N. J. Warren, A. Chahal, K. Amps, A. Wood, R. Weightman, E. Wang, H. Moore and S. P. Armes, ACS Centr. Sci., 2016, 2, 65-74). The gel modulus and chemical structure of this synthetic hydrogel are similar to that of natural mucins, which are implicated in the mechanism of diapause for mammalian embryos. Does stasis induction occur merely because of the very soft nature of such hydrogels or does chemical functionality also play a role? Herein, we address this key question by designing a new hydrogel of comparable softness in which the PGMA stabilizer chains are replaced with non-hydroxylated poly(ethylene glycol) [PEG]. Immunolabeling studies confirm that hPSC colonies immersed in such PEG-based hydrogels do not enter stasis but instead proliferate (and differentiate if no adhesion substrate is present). However, pluripotency is retained if an appropriate adhesion substrate is provided. Thus, the chemical functionality of the hydrogel clearly plays a decisive role in the stasis induction mechanism.

Mucin-Inspired Thermoresponsive Synthetic Hydrogels Induce Stasis in Human Pluripotent Stem Cells and Human Embryos

Human pluripotent stem cells (hPSCs; both embryonic and induced pluripotent) rapidly proliferate in adherent culture to maintain their undifferentiated state. However, for mammals exhibiting delayed gestation (diapause), mucin-coated embryos can remain dormant for days or months in utero, with their constituent PSCs remaining pluripotent under these conditions. Here we report cellular stasis for both hPSC colonies and preimplantation embryos immersed in a wholly synthetic thermoresponsive gel comprising poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) [PGMA55-PHPMA135] diblock copolymer worms. This hydroxyl-rich mucin-mimicking nonadherent 3D gel maintained PSC viability and pluripotency in the quiescent G0 state without passaging for at least 14 days. Similarly, gel-coated human embryos remain in a state of suspended animation (diapause) for up to 8 days. The discovery of a cryptic cell arrest mechanism for both hPSCs and embryos suggests an important connection between the cellular mechanisms that evoke embryonic diapause and pluripotency. Moreover, such synthetic worm gels offer considerable utility for the short-term (weeks) storage of either pluripotent stem cells or human embryos without cryopreservation.

Pleomorphism of the nuclear envelope in breast cancer: a new approach to an old problem

In routine practice, nuclear pleomorphism of tumours is assessed by haematoxylin staining of the membrane-bound heterochromatin. However, decoration of the nuclear envelope (NE) through the immunofluorescence staining of NE proteins such as lamin B and emerin can provide a more objective appreciation of the nuclear shape. In breast cancer, nuclear pleomorphism is one of the least reproducible parameters to score histological grade, thus we sought to use NE proteins to improve the reproducibility of nuclear grading. First, immuno-fluorescence staining of NE as well as confocal microscopy and three-dimensional reconstruction of nuclei in cultured cells showed a smooth and uniform NE of normal breast epithelium in contrast to an irregular foldings of the membrane and the presence of deep invaginations leading to the formation of an intranuclear scaffold of NE-bound tubules in breast cancer cells. Following the above methods and criteria, we recorded the degree of NE pleomorphism (NEP) in a series of 273 invasive breast cancers tested by immunofluorescence. A uniform nuclear shape with few irregularities (low NEP) was observed in 135 cases or, alternatively, marked folds of the NE and an intranuclear tubular scaffold (high NEP cases) were observed in 138 cases. The latter features were significantly correlated (P-value <0.002) with lymph node metastases in 54 histological grade 1 and in 173 cancers with low mitotic count. Decoration of the NE might thus be regarded as a novel diagnostic parameter to define the grade of malignancy, which parallels and enhances that provided by routine histological procedures.

Catalytic Activities of G1Cyclin-Dependent Kinases and Phosphorylation of Retinoblastoma Protein in Mobilized Peripheral Blood CD34+Hematopoietic Progenitor Cells

Depending on the source of cells, the cell cycle status of hematopoietic stem and progenitor cells capable of repopulating the marrow of transplant recipients is controversial. In this study, using biochemical methods, the cell cycle status of mobilized CD34+ cells was analyzed. It was demonstrated in CD34+ cell extracts that there was high catalytic activity of G(1) cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) but low activity of CDK2. This was in contrast to the resting reference cells that showed only minimal or no activity of these CDKs. Since at the G0-->G1-->S transition CDK4/6 and CDK2 sequentially phosphorylate the retinoblastoma protein (pRB), its phosphorylation status was analyzed. Previously, we showed that p110RB was unphosphorylated at serine (Ser)-608 in CD34+ cells, consistent with the ability to suppress cell growth. Here, it was established that this form of pRB was phosphorylated at Ser-780, Ser-795, and Ser-807/811 in CD34+ but not in resting reference cells. This result was therefore consistent with the presence of high CDK4/6 activities in CD34+ cells. Conversely, CDK2 activity was low and the pRB residues Ser-612 and threonine (Thr)-821, which are exclusively phosphorylated by CDK2 in conjunction with either cyclin E or A, were unphosphorylated in >90% of CD34+ cells. We therefore show for the first time the exact position of mobilized CD34+ cells within the cell cycle; that is, they do not reside in G0 but in early G1 phase and did not cross the restriction point into late G1 phase.

Regulation of the quiescence-induced genes: quiescin Q6, decorin, and ribosomal protein S29

The transition from growth to quiescence is deeply deranged in cancer cells. Expression of the quiescence-induced genes, quiescin Q6, decorin, and S29, was examined in important physiological states and in several cell types. Senescent fibroblasts expressed neither Q6 nor decorin mRNAs. The quiescins were induced in serum-deprived cultures. Trypsinized cells, which rapidly reattached to the culture dish, expressed Q6, S29, and decorin mRNAs at reduced levels, compared to those that remained in suspension. Expression of Q6 and S29 mRNAs in endothelial cells was low in growth phase and high in quiescent cells. Q6 and S29 mRNAs were found in a large variety of human tissues. The quiescin Q6 protein was detected in WI38 cell extracts and in conditioned medium from quiescent cells. A complex regulation of the quiescins by growth and attachment status in specific cell types may be of importance in pathological growth regulation and the development of cancer.

Nuclear phospholipids in human lymphocytes activated by phytohemagglutinin

Using a specific ultracytochemical technique, the labelling with phospholipase A2-gold complex, we have followed nuclear phospholipids (PL) along the G1 phase in human lymphocytes activated by PHA. Our data point out two main results relating nuclear PL to the transcriptional activity, characteristic of the G1 phase, during which many different molecules necessary both for progression through G1 and for the start of S phase are synthesized. PL quantitative changes parallel those of hnRNPs and snRNPs, which are markers of the levels of transcriptional activity and processing. We found that nuclei of G0 lymphocytes, with a very low transcription level, are poor of PL as well as of RNPs. The amount of PL increases in activated lymphocytes, along all G1, until the beginning of S phase. At the same time, hnRNPs and snRNPs strongly increase and maintain higher levels than in control cells, till the beginning of S phase. PL are localized on nuclear structures where also RNPs involved in transcription and splicing, are located, i. e. perichromatin fibrils, interchromatin granules and the dense fibrillar component of the nucleolus. Since it is known that during S phase nuclear PL decrease, while both the enzyme activities related to their breakdown and their hydrolysis products increase, PL seem to be involved in the generation of signal molecules triggering DNA replication. We suggest that PL in the nucleus can be involved in multiple functions, depending on the phase of the cell cycle.

In childhood acute lymphoblastic leukemia the hypophosphorylated retinoblastoma protein, p110RB, is diminished, as compared with normal CD34+ peripheral blood progenitor cells

Acute lymphoblastic leukemia (ALL) of childhood arises from dysregulated clonal expansion of immature lymphoid precursor cells that fail to differentiate into functional lymphocytes. The cell-cycling status of ALL cells shares many common features with that of normal CD34+ hematopoietic progenitor cells, such as low number of resting G0 and cycling S phase cells even though the growth fraction is high. Thus, ALL cells should be in a long G1 phase. Phosphorylation of the retinoblastoma protein is a crucial step in cell-cycle progression from G0/early G1 to late G1/S phase. We therefore analyzed the G1 distribution of these two immature cell populations by immunostaining and Western blot. Bone marrow samples from children with ALL at diagnosis as well as purified CD34+ cells, before and after in vitro stimulation with cytokines, were investigated for the expression of hypophosphorylated p110RB (early G1 phase), total retinoblastoma protein, statin (G0 phase), bromo-deoxyuridine (S phase), proliferating cell nuclear antigen, and p120 (cycling cells). Compared with unstimulated CD34+ cells (95.8 +/- 1.2%) the component of ALL cells containing hypophosphorylated p110RB (16.3 +/- 13.2%) was significantly reduced (p = 0.00018), whereas only a minor difference could be detected for the proportion of cycling cells (p = 0.03), and no difference in G0 and S phase cells (p > 0.05). Our results indicate that, as opposed to unstimulated CD34+ cells, the majority of ALL cells are beyond the restriction point and therefore irreversible committed to DNA replication and mitosis.

Proliferation of differentiated glial cells in the brain stem

Classical studies of macroglial proliferation in muride rodents have provided conflicting evidence concerning the proliferating capabilities of oligodendrocytes and microglia. Furthermore, little information has been obtained in other mammalian orders and very little is known about glial cell proliferation and differentiation in the subclass Metatheria although valuable knowledge may be obtained from the protracted period of central nervous system maturation in these forms. Thus, we have studied the proliferative capacity of phenotypically identified brain stem oligodendrocytes by tritiated thymidine radioautography and have compared it with known features of oligodendroglial differentiation as well as with proliferation of microglia in the opossum Didelphis marsupialis. We have detected a previously undescribed ephemeral, regionally heterogeneous proliferation of oligodendrocytes expressing the actin-binding, ensheathment-related protein 2'3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), that is not necessarily related to the known regional and temporal heterogeneity of expression of CNPase in cell bodies. On the other hand, proliferation of microglia tagged by the binding of Griffonia simplicifolia B4 isolectin, which recognizes an alpha-D-galactosyl-bearing glycoprotein of the plasma membrane of macrophages/microglia, is known to be long lasting, showing no regional heterogeneity and being found amongst both ameboid and differentiated ramified cells, although at different rates. The functional significance of the proliferative behavior of these differentiated cells is unknown but may provide a low-grade cell renewal in the normal brain and may be augmented under pathological conditions.

Thymocytopoiesis in aging: the bone marrow-thymus axis

Manifestations of aging in the mature T lymphocyte compartment have been attributed, to a major extent, to effects of the involuted thymus, at the thymic microenvironment level. However, since generation of T lymphocytes starts from hemopoietic stem cells that settle in the thymus and differentiate there, aging effects on the stem cells, and as a consequence, on the bone marrow (BM)-thymus axis, may also have an impact on patterns of thymocytopoiesis and on age-related thymus remodeling. This communication reviews our studies designed to determine whether BM cells manifest any aging effects that become overt in the resulting thymocytes. The experiments were performed by seeding of BM cells onto lymphoid-depleted fetal thymus (FT) explants, to enable distinguishing between processes that occur in the BM and those that are caused by the aging thymic microenvironment. The data show changes in the developmental potential of BM-derived cells, as reflected from the kinetics of cell cycle and intermediate steps from stem cell settling in the thymus to an early stage at the transition from CD4(-)CD8(-), double negative (DN), to CD4(+)CD8(+), double positive (DP) thymocytes. In addition, we have demonstrated that these early developmental steps of thymocytopoiesis are subject to feedback regulation by mature T cells, and the extent of regulation may be altered in old age. The pattern of T lymphocyte generation in aging is thus a result of dynamic changes in thymic, as well as extrathymic functions, along the sequential developmental steps from the stem cell to the ultimate mature cell.

Matrix metalloproteinase 2 (gelatinase A) regulates glomerular mesangial cell proliferation and differentiation

A biologic role for the 72-kDa gelatinase A (matrix metalloproteinase 2; MMP-2), beyond simple extracellular matrix turnover, was evaluated in glomerular mesangial cells. To determine the significance of MMP-2 secretion for the acquisition of the inflammatory phenotype, we reduced the constitutive secretion of MMP-2 by cultured mesangial cells with antisense RNA expressed by an episomally replicating vector or with specific anti-MMP-2 ribozymes expressed by a retroviral transducing vector. The phenotype of the transfected, or retrovirally infected, cells was profoundly altered from the activated state and closely approximated that of quiescent cells in vivo. The prominent differences included a change in the synthesis and organization of the extracellular matrix, loss of activation markers, and a virtually total exit from the cell cycle. Reconstitution with exogenous active, but not latent MMP-2, induced a rapid return to the inflammatory phenotype in vitro. This effect was specific to MMP-2, because the closely related MMP-9 did not reproduce these changes. Furthermore, this pro-inflammatory effect of MMP-2 is dependent upon the active form of the enzyme, which can be produced by an autocatalytic activation process on the mesangial cell plasma membrane. It is concluded that MMP-2 acts directly upon mesangial cells to permit the development of an inflammatory phenotype. Specific inhibition of MMP-2 activity in vivo may represent an alternate means of ameliorating complex inflammatory processes by affecting the phenotype of the synthesizing cells, per se.

Immunohistochemical analysis of statin in colorectal adenocarcinoma, polyps, and normal mucosa

PURPOSE

The search for an understanding of the kinetics of the malignant cell is an ongoing focus of research. The aim of the present study was to determine whether there were any differences in the expression of statin, a nonproliferation-specific nuclear protein, among different colorectal tissues and whether there is any relationship between statin presence and neoplastic aggressivity.

METHODS

The study population consisted of specimens from 19 patients who underwent resection for carcinoma, one for villous adenoma, and seven for colonoscopic polypectomies. Tissue samples were taken from the center of the specimen and from mucosa 10 cm from the lesion.

RESULTS

Statin immunoreactivity was evaluated by counting stained nuclei in ten randomly chosen fields, and percent of positive cells was calculated. Average percentage of statin-positive cells was 34.33 +/- 6.81 in the normal crypt, 44.42 +/- 7.28 for polyps, and 7.74 +/- 5.67 for carcinomas (significantly lower than normal mucosa and polyps; P < 0.001).

CONCLUSION

Statin expression is dramatically diminished in invasive carcinoma tissue, but it did not help determine aggressivity with respect to Dukes stage.

Molecular markers of senescence in fibroblast-like cultures

The loss of replicative capacity in vitro of normal human diploid fibroblasts is a model for studying molecular changes that accompany both regulated growth control and cellular senescence. We describe the molecular phenotype of senescent fibroblasts in terms of markers that are altered with proliferative decline. We describe these markers by analyzing pathways and associated mechanisms related to the responsiveness of proliferatively competent and senescent cells to growth signals including changes in the extracellular environment, growth factors, growth factor receptors, secondary messengers, cell-cycle progression, transcription factors, and the fidelity of DNA synthesis. There is an abundance of molecular markers for senescence in culture at every level of information transfer. Although it seems clear that some alterations in gene expression with senescence are the result of specific changes in upstream events, more global dysregulation of coordinated growth control point to as yet undefined mechanisms.

Increased levels of statin, a marker of cell cycle arrest, in response to hippocampal neuronal injury

Injured neurons in the CNS are known to synthesize high levels of proliferation related oncogene products and heat shock proteins without dividing. Statin is a cell cycle regulated nuclear phosphoprotein, selectively associated with the non-proliferative state in a wide variety of cell types. In the present study, neuronal statin was examined following lethal or sublethal neuronal injuries in the hippocampus of Alzheimer's disease patients, in rats receiving kainate lesions to the dorsal hippocampus and in entorhinal cortex lesioned rats. Immunolabelling of nuclear statin showed that statin immunoreactivity increased preferentially in CA1 pyramidal neurons of the hippocampus in Alzheimer's disease. In kainate lesioned rats, statin immunoreactivity was markedly induced in the CA3 hippocampal region in association with neuronal loss. Entorhinal cortex lesioned rats showed a transient induction of statin between 2 and 6 days post lesion in CA1 neurons. However, cell counts in entorhinal cortex lesioned rats remained unaltered in the CA1 and granule cell layers during the entire 30 day time course, indicating that increased statin levels are not secondary to neuronal degeneration and are not necessarily accompanied by irreversible neuronal death. It is concluded that, in addition to proliferation related gene products, neuronal injury induces an increase in levels of statin, a nuclear marker of cell cycle arrest. Furthermore, statin may be a potentially useful marker of injurious neuronal stress, even under conditions that do not necessarily lead to irreversible cell death.

Regulation of c-fos expression in senescing Werner syndrome fibroblasts differs from that observed in senescing fibroblasts from normal donors

The Werner syndrome (WS) is a segmental progeroid syndrome caused by a recessive mutation (WRN) mapped to 8p12. The replicative life spans of somatic cells cultured from WS patients are substantially reduced compared to age-matched controls. Certain molecular concomitants of the replicative decline of normal fibroblast cultures have recently been defined, and it appears that multiple changes in gene expression accompany normal cell senescence. If the mechanisms by which WS cells exit the cell cycle were entirely comparable, the molecular markers of senescence should be identical in normal and WS cells. We find that this is not the case. The constitutive expression of statin, a nuclear protein associated with the nonproliferating state, was comparably expressed in normal and WS senescent cells. Likewise, the steady state levels of p53, a protein known to be involved in the G1 checkpoint of the cell cycle, were similar in early-passage fibroblasts from normal and WS subjects. The levels of p53 were not increased in senescent fibroblasts, whether derived from normal or WS subjects. By contrast, the inducibility of mRNA and protein expression of the c-fos protooncogene is preserved in late-passage WS cells. This is in contrast to what is observed in late-passage fibroblasts from normal subjects. Additional genotypes will have to be examined, however, to determine the specificity of this new aspect of the WS phenotype.

Nuclear phospholipids during the adaptation of human EUE cells to hypertonic stress

The phospholipid component of interphase nuclei was analysed in EUE cells (an established cell line from embryonic human epithelium) grown in an isotonic culture medium and during the adaptation process to a hypertonic medium, using a highly specific ultracytochemical procedure, viz. labelling with the phospholipase A2 gold-complex. Within the nucleus, the phospholipids were localized in domains involved in different steps of the synthesis and processing of the RNA. These localizations did not vary at the two key steps of the adaptation process to hypertonic medium: short-term treatment (6 h) representing critical shock condition, and long-term growth (5 days) representing the adapted cells under survival conditions. On the contrary, deep changes of the labelling intensity of phospholipids at these sites occurred at the different times of hypertonic treatment and followed the same course as those observed in the ultramorphological patterns of transcription: the chromatin condensation, as evaluated by image analysis, the permanent nucleolar components, the interchromatin and the perichromatin granules. These data endorse the hypothesis that nuclear phospholipids could be involved in different steps of the transcriptional activity. They are indicative of the deep changes occurring in the EUE cells submitted to hypertonic stress.

Proliferative activity at colonic anastomoses as determined by statin. A nonproliferation-specific nuclear protein

PURPOSE

One theory of anastomotic recurrence in large bowel carcinoma is that epithelial hyperplasia at the suture line causes metachronous carcinoma.

METHODS

S44, a monoclonal antibody directed against statin, a nuclear protein expressed in quiescent cells, was used to determine whether the anastomosis represents an area with a high proliferation rate. During follow-up colonoscopic examination of patients who had undergone previous resection for colorectal carcinoma, biopsies were taken from the anastomotic site and from the mucosa 10 to 15 cm from the anastomosis. One side of 10 well-oriented crypts was counted for each patient with the number of nuclei positive for statin being determined by the presence of dark brown reaction product.

RESULTS

The average percentages of statin-positive cells varied between 19.4 and 44.4 (average, 31.3 +/- 6.5) for the normal mucosa and 22.8 to 35.1 (average, 29.98 +/- 3.67) for the anastomotic mucosa. The differences were not significant. There were no differences between those patients in whom the postoperative time elapsed was two years or less and those greater than two years.

CONCLUSION

This study is unique in that the proliferative activity at the site of colonic anastomosis was determined in a clinical setting, and patients in which the anastomoses were created anywhere from 1 to 14 years earlier were included. Using S44 as a marker, this study does not support the theory that suture line recurrence is a result of an enhanced proliferation rate.

Characterization of 57 kDa statin as a true marker for growth arrest in tissue by its disappearance from regenerating liver

Statin, a 57 kDa nuclear protein, is lost from quiescent fibroblasts in culture when they are induced to enter the cell cycle by feeding with growth factors, or by removal of contact inhibition. In order to investigate changes in statin expression during the transition from a quiescent to a cycling state in situ, we performed 70% partial hepatectomy on rats and analyzed the regenerating liver by immunofluorescence microscopy with antistatin monoclonal antibodies (S44 mAb), and by immunoblotting of liver proteins in cytoplasmic and enriched nuclear/cytoskeletal fractions. Western blot analysis showed that rat hepatocytes in situ contain a nuclear 57 kDa form of statin, as seen in cultured fibroblasts; however additional S44-immunoreactive polypeptides with molecular weights of 53 and 110 kDa are also present in both cytoplasmic and nuclear/cytoskeletal fractions. Immunofluorescence microscopy indicates that the proportion of S44-positive hepatocyte nuclei drops to approximately 60% within 24 hours after hepatectomy, a time period when re-entry of hepatocytes into the cell cycle is first observed. On Western blots of hepatocyte nuclear/cytoskeletal proteins obtained 24 hours after hepatectomy, the 57 kDa form of statin is markedly reduced. These results suggest that, although in liver the S44 antibody recognizes three proteins (53 kDa, 57 kDa, and 110 kDa), the 57 kDa in intact liver, similar to cultured fibroblasts, is the only polypeptide recognized by the statin antibody that disappears when hepatocytes are induced to re-enter the cell cycle from a quiescent state.

Molecular biology of aging

Aging is an extremely complex biologic phenomenon of immense importance. Currently we have only a poor and incomplete understanding of the fundamental molecular mechanisms involved. Despite numerous observations and diverse theories, no unifying or proven hypotheses have emerged. It is reasonable to conclude, however, that aging is a multifactorial process composed of both genetic and environmental components. Each physiologic system within an organism, each tissue within a system, and each cell type with a tissue appears to have its own trajectory of aging. Thus, aging must be studied as parts of a whole and understood as the sum of its parts. Cellular "clocks" exist and operate in the absence of higher-order "clocks". However, higher-order clocks are certainly in place in vivo, but their relationship to cellular clocks is not well understood. All aging changes have a cellular basis, and aging is perhaps best studied, fundamentally, at the cellular level under defined and controlled environmental conditions. Aging changes at the cellular level must be viewed, however, as components of a hierarchical, dynamic, and interacting network whose functional integrity progressively deteriorates with time. The powerful tools of molecular biology are now being applied by scientists to evaluate the leading hypotheses. The results of these studies should serve to advance our understanding of aging and to focus future research efforts. This work should provide the scientific foundation to enhance the quality of life for people suffering the failings of age.

A novel cDNA corresponding to transcripts expressed in retina post-mitotic neurons

The long term objective of this study is to isolate genes specifically expressed at the onset of neuronal cell cycle withdrawal. As an experimental paradigm we have used a quail neuroretinal cell clone (clone K2) immortalized by a thermosensitive mutant of Rous Sarcoma Virus. K2 cells proliferate at 36 degrees C but stop synthesizing DNA after a shift to 41.5 degrees C. We have constructed a cDNA library from K2 cells transferred to 41.5 degrees C and autosubtracted with RNAs from K2 cells maintained at 36 degrees C. This strategy has led to the isolation of cDNAs which recognize mRNAs expressed in quail neuroretina (NR) during development. We report here one of these cDNAs, cDNA QN1, that hybridizes with transcripts expressed in retina neurons, in parallel with their withdrawal from the cell cycle. QN1 ORF codes for a 138 kDa polypeptide corresponding to the protein observed in Western blot analysis. A role of QN1 product(s) on neuronal quiescence is suggested by the positive effect of an antisense oligonucleotide on DNA synthesis of K2 cells.

Prospects for the genetics of human longevity

Longevity varies between and within species. The existence of species-specific limit to human life-span and its partial heritability indicate the existence of genetic factors that influence the ageing process. Insight into the nature of these genetic factors is provided by evolutionary studies, notably the disposable soma theory, which suggests a central role of energy metabolism in determining life-span. Energy is important in two ways. First, the disposable soma theory indicates that the optimum energy investment in cell maintenance and repair processes will be tuned through natural selection to provide adequate, but not excessive, protection against random molecular damages (e.g. to DNA, proteins). All that is required is that the organism remains in a sound condition through its natural expectation of life in the wild environment, where accidents are the predominant cause of mortality. Secondly, energy is implicated because of the intrinsic vulnerability of mitochondria to damage that may interfere with the normal supply of energy to the cell via the oxidative phosphorylation pathways. Oxidative phosphorylation produces ATP, and as a by-product also produces highly reactive oxygen radicals that can damage many cell structures, including the mitochondria themselves. Several lines of evidence link, on the one hand, oxidative damage to cell ageing, and on the other hand, energy-dependent antioxidant defences to the preservation of cellular homeostasis, and hence, longevity. Models of cellular ageing in vitro allow direct investigation of mechanisms, such as oxidative damage, that contribute to limiting human life-span. The genetic substratum of inter-individual differences in longevity may be unraveled by a two-pronged reverse genetics approach: sibling pair analysis applied to nonagenarian and centenarian siblings, combined with association studies of centenarians, may lead to the identification of genetic influences upon human longevity. These studies have become practicable thanks to recent progress in human genome mapping, especially to the development of microsatellite markers and the integration of genetic and physical maps.

Expression of the non-proliferation-specific protein, statin, in grey matter neuroglia of the aging rat brain

The monoclonal antibody, S-44, identifies statin, a 57 kDa nuclear protein which appears to be expressed exclusively in non-proliferating cells. We previously demonstrated that in the aging rat corpus callosum approximately one third of neuroglia are statin-negative, suggesting the existence of an unexpectedly large cycling glial compartment. In the present study, double-labeling of individual cultured astroglia with [3H]thymidine and the S-44 antibody provided direct evidence for the non-proliferative status of statin-positive cells. The S-44 antibody was used to immuno-localize statin and thereby determine growth fractions for neuroglia in various grey matter regions of 3-, 18-, and 33-month-old rats. The proportion of statin-negative (cycling) cells for the three ages combined ranged from about 24% in the molecular layer of the dentate gyrus to 38% in the molecular layer of the parietal cortex. In most regions surveyed total glial counts and proportions of statin-positive and -negative cells did not vary significantly as a function of advancing age. These results suggest that (i) as in corpus callosum, pools of cycling neuroglia in various grey matter regions are far in excess of those previously predicted by S-phase labeling with [3H]thymidine or BUdR, and (ii) ratios of proliferating-to-quiescent neuroglia are tightly regulated over much of the animal's adult life span. These conserved ratios may be used as markers of normal CNS senescence, and deviations thereof may indicate the presence and extent of intervening neuropathologic processes.

Proliferative activity of colonic mucosa at different distances from primary adenocarcinoma as determined by the presence of statin: a nonproliferation-specific nuclear protein

The field change is one hypothesis concerning the development of colorectal carcinoma. Removal of a carcinoma without its entire surrounding altered mucosa may result in the development of a recurrence. S44, a monoclonal antibody directed against statin, a nuclear protein expressed in nonproliferating cells in either a quiescent or senescent state, was used to determine the rate of cell growth in colorectal mucosa at different distances from carcinomas. The specimens of 18 patients undergoing resection of a colorectal carcinoma were immediately opened after operation, and strips of mucosa were taken at distances of 1 cm, 5 cm, and 10 cm from the carcinoma. For each location, 10 longitudinally oriented crypts were evaluated for statin-positive cells identified by the presence of a dark brown peroxidase-conjugated antibody reaction product. The average percentage of statin-positive cells per crypt was significantly lower at a 1-cm distance from the carcinoma compared with the mucosa located 5 and 10 cm from the carcinoma (20.89 +/- 4.33 at 1 cm, 32.41 +/- 5.27 at 5 cm, and 34.23 +/- 6.45 at 10 cm). None of the calculated parameters showed any significant difference between the 5-cm and 10-cm locations. The fact that the proliferation rate of the mucosal cells returns to the normal level at 5 cm from the margin of the carcinoma suggests that cells located within this distance still retain proliferative potential even though they are morphologically indistinguishable from their normal counterparts. We conclude that failure to remove this transitional, potentially proliferative mucosa may result in subsequent development of anastomotic or perianastomotic recurrences.

Cloning and expression of SAG: a novel marker of cellular senescence

Unlike immortalized cell lines, normal human fibroblasts in culture undergo replicative senescence in which the number of population doublings is limited. While fibroblasts display a variety of changes as they senesce in vitro, little is known about how gene expression varies as a function of population doubling level. We have used differential hybridization screening to identify human genes that are preferentially expressed in senescent cells. While we found several isolates that were up-regulated in late-passage cells, all appeared to be variants of the same cDNA, which we named senescence-associated gene (SAG). Our data show that SAG expression is threefold higher in senescent fibroblasts and closely parallels the progressive slowdown in growth potential, but is not cell-cycle regulated. Thus, SAG serves as an accurate marker for fibroblast growth potential during replicative senescence. Further studies demonstrated that SAG is a novel gene active in nearly all tissue types tested and that it is conserved through evolution. DNA sequencing data indicate that SAG contains a potential DNA-binding domain, suggesting that SAG may function as a regulatory protein.

Expression of a novel nuclear protein is correlated with neuronal differentiation in vivo

We report the production of a monoclonal antibody (MAb 526) that recognizes a novel, developmentally regulated nuclear protein expressed in neurons throughout the rat nervous system. Analysis of whole brain and cell nuclear extracts by SDS-PAGE and immunoblotting determined that MAb 526 recognizes a single nuclear protein (np) of apparent molecular weight 42 kD, designated np526, as well as a slightly larger (ca. 44 kD) cytoplasmic protein. Light microscopic immunocytochemistry showed np526 to be present in neurons of all types throughout the central and peripheral nervous systems. Nuclei of both fibrous and protoplasmic astrocytes were also immunoreactive, but oligodendrocyte nuclei were negative. Positive, but highly variable immunocytochemical staining of nonneural cell nuclei in a variety of other tissues was also observed. Electron microscopic (EM) immunocytochemistry using pre-embedding peroxidase methods revealed that np526 is associated with euchromatin or with the edges of condensed chromatin bundles in neurons, indicating that it is likely to be a chromosomal protein. Most interestingly, the expression of np526 was found to be developmentally regulated in brain. Immunocytochemical analysis of the developing cerebral cortex from embryonic day (E) 16 to postnatal day (P) 4 and cerebellum from P4 to P18 revealed that np526 first appears in central neurons following the cessation of mitosis and that the intensity of nuclear staining increases during subsequent neuronal maturation. To our knowledge, np526 is the first presumptive chromosomal protein whose expression has been precisely correlated with the early postmitotic differentiation of mammalian neurons.

Statin immunolocalization in human brain tumors. Detection of noncycling cells using a novel marker of cell quiescence

Surgical specimens of 35 human brain tumors were examined with a novel monoclonal antibody, S-44, immunoreactive to statin, a nuclear protein specifically expressed in quiescent (noncycling) G0-phase cells. Benign tumors typically were statin positive with labeling indices (LI) between 22% and 96%: acoustic schwannomas (n = 3, mean = 29.9 +/- 19.4%); meningiomas (n = 4, mean = 59.0 +/- 15.1%); pituitary adenomas (n = 3, mean = 79.9 +/- 28.2%), and an epidermoid cyst (41.0%). By contrast, the statin LI of 18 of 24 (75%) malignant brain tumors was less than or equal to 2%: medulloblastomas (n = 7, mean = 0.3 +/- 0.2%); anaplastic astrocytomas (n = 3, mean = 1.6 +/- 2.7%); glioblastomas (n = 10, mean = 10.3 +/- 14.4%); metastatic carcinomas (n = 3, mean = 3.0 +/- 4.6); and a germinoma (0.2%). The vascular endothelium among diverse tumors typically was statin positive. All 21 tumors with a statin LI less than 10% were malignant, and all nine tumors with a statin LI greater than 40% were benign. The statin LI of benign tumors (n = 11, mean = 55.1 +/- 26.7%) was significantly higher than that of the malignant tumors (n = 24, mean = 5.2 +/- 10.5%, P less than 0.001). The absence of statin expression is a new way to determine the malignancy of human brain tumors. The statin LI may be useful to guide the prognosis and treatment of individual patients. The mechanisms that control statin expression are important in therapy seeking to shift the proliferating, cycling cells to the quiescent, G0 compartment.

Granular presence of terminin is the marker to distinguish between the senescent and quiescent states

We have previously identified statin, a nonproliferating-cell-specific nuclear protein of 57,000 dalton whose presence can be used to distinguish between growing and nongrowing cells. In this report we identify another protein, terminin, whose presence (by immunofluorescence microscopy) can be used to distinguish between temporarily and permanently growth-arrested cells. Thus terminin is a marker to separate the senescent from the quiescent state. By means of an unique monoclonal antibody (mAb1.2), the presence of terminin is recognized as granules in the cytoplasm of in vitro aged fibroblasts; these granules are not found in serum-starved, contact-inhibited, growing or transformed fibroblasts, except for those cells experiencing the initiation of apoptosis due to long-term deprivation of nutrients. Preliminary histochemical studies show that terminin is also found in the superficial epithelial layer of the esophagus, where terminal differentiation is followed by apoptosis and sloughing off into the lumen. Biochemical characterization by Western blot shows the terminin antibody recognizing a protein of 84 kilodalton (kDa) in growing and quiescent cells, whereas in senescent cells a protein of 57 kDa is recognized; this result suggests that a senescence-dependent protease may cleave the 84 kDa protein to 57 kDa. This proteolytic action seems to render the specific antigenic epitope exposed in its native state and accessible to the terminin antibody by immunofluorescence microscopy. It is this product of posttranslational modification in the form of a cytoplasmic 57 kDa protein that is the marker distinguishing between senescence and quiescence.

Expression of statin, a non-proliferation-dependent nuclear protein, in the postnatal rat brain: evidence for substantial retention of neuroglial proliferative capacity with aging

Statin is a 57 kDa protein expressed in nuclei of reversibly and irreversibly growth-arrested (Go-phase) cells. In this report, immunohistochemical localization of statin in the developing and aging rat brain was achieved using the monoclonal antibody, S-44. On postnatal day 2, post-migratory neurons in the developing cerebral cortex were statin-positive. Many statin-negative cells were observed in the lateral subependymal zone of the lateral ventricle. By postnatal day 10, most neuronal nuclei were statin-positive although small numbers of statin-negative neurons were still encountered in the lateral subependymal zone and hippocampal dentate gyrus. At 3, 18 and 33 months, all neuronal nuclei surveyed were statin-positive. These results support the contention that, save for the postnatal persistence of 'germinal zones' such as the subependymal region and dentate gyrus, neuronal proliferation in the rat is largely completed by the time of birth. In striking contrast to neuronal statin expression, a significant fraction of neuroglia in both grey and white matter remains statin-negative at all ages examined. In the corpus callosum, 33.2%, 34.0% and 34.7% of glial nuclei were statin-negative at 3, 18 and 33 months, respectively. These findings indicate that: (i) even in senescent brain, the cycling (statin-negative) glial pool is substantially larger than previously surmised from S-phase labeling experiments; and (ii) during aging, the ratio of noncycling-to-cycling neuroglia remains very tightly regulated. Examination of other non-neuronal cell types revealed that most, if not all, ependymal and choroid plexus epithelial cells were statin-positive in the neonatal and adult brains in keeping with the predominantly prenatal proliferation of these tissues. Our results indicate that statin immunolabeling using the S-44 antibody is a powerful technique for the in situ identification of non-proliferating cells in the developing and aging nervous system.