Transfection of C6 glioma cells with the bax gene and increased sensitivity to treatment with cytosine arabinoside

Genes known to be involved in the regulation of apoptosis include members of the bcl-2 gene family, such as inhibitors of apoptosis (bcl-2 and bcl-xl) and promotors of apoptosis (bax). The authors investigated a potential approach for the treatment of malignant gliomas by using a gene transfection technique to manipulate the level of an intracellular protein involved in the control of apoptosis. The authors transfected the murine bax gene, which had been cloned into a mammalian expression vector, into the C6 rat glioma cell line. Overexpression of the bax gene resulted in a decreased growth rate (average doubling time of 32.96 hours compared with 22.49 hours for untransfected C6, and 23.11 hours for clones transfected with pcDNA3 only), which may be caused, in part, by an increased rate of spontaneous apoptosis (0.77 +/- 0.15% compared with 0.42 +/- 0.08% for the vector-only transfected C6 cell line; p = 0.038, two-tailed Student's t-test). Treatment with 1 microM of cytosine arabinoside (ara-C) resulted in significantly more cells undergoing apoptosis in the cell line overexpressing bax than in the vector-only control cell line (23.57 +/- 2.6% compared with 5.3 +/- 0.7% terminal deoxynucleotidyl transferase--mediated biotinylated--deoxyuridine triphosphate nick-end labeling technique-positive cells; p = 0.007). Furthermore, measurements of growth curves obtained immediately after treatment with 0.5 microM ara-C demonstrated a prolonged growth arrest of at least 6 days in the cell line overexpressing bax. These results can be used collectively to argue that overexpression of bax results in increased sensitivity of C6 cells to ara-C and that increasing bax expression may be a useful strategy, in general, for increasing the sensitivity of gliomas to antineoplastic treatments.

The profile of gene expression and role of nuclear factor kappa B on glomerular injury in rats with Thy-1 nephritis

Mesangioproliferative glomerulonephritis (MsPGN) is a disease of high incidence in humans. Rats with Thy-1 nephritis (Thy-1 N) are used as an animal model for studying MsPGN. Although several studies have demonstrated that many pathological factors could cause the injury of glomerular mesangial cells (GMCs) in Thy-1 N, changes of profile and the molecular mechanism of the disease (i.e. the role of transcription factors) at intervals remain unclear. The purpose of this study was to identify the changes in gene expression profile and to observe the role of nuclear factor kappa B (NF-kappaB) on the pathological change of renal tissue in Thy-1 N rats. Our results showed that the pathological changes of GMCs in Thy-1 N included three phases: apoptosis (40 min), necrosis (24 h) and proliferation (7 days). Concomitantly, at 40 min and on day 7, the up-regulation of 341 genes and 250 genes were observed, while 392 genes and 119 genes were down-regulated in Thy-1 N. Expression of interleukin (IL)-1beta, IL-6, proliferating cell nuclear antigen, alpha-smooth muscle actin, collagen type IV and excretion of urinary protein was increased in rats with Thy-1 N and decreased in pyrrolidine dithiocarbamate-treated rats with Thy-1 N. These data indicated that the significant changes in the gene profile were coupled with the pathological changes of Thy-1 N, and activation of NF-kappaB may contribute to the pathogenesis of GMCs apoptosis, proliferation, extracelluar matrix accumulation and proteinuria in Thy-1 N.

Overexpression of bax in human glioma cell lines

OBJECT

Cells that lose their ability to undergo apoptosis may promote the development of neoplasms and result in resistance to clinical treatment with DNA-damaging modalities such as radio- and chemotherapy. Four established human glioma cell lines that are resistant to apoptosis were transfected with the proapoptotic gene bax and assessed for their sensitivity to a proapoptotic stimulus.

METHODS

Two cell lines had a wild-type p53 genotype (U87 and D247MG) and two had mutant p53 genotypes (U138 and U373). Constitutive overexpression of murine bax was achieved in U138 and U373 only, which resulted in an increased sensitivity of these lines to the apoptosis-inducing effect of cytosine arabinoside (ara-C). Multiple attempts to produce constitutive overexpression of bax in U87 and D247MG cells resulted in spontaneous, near-complete cell loss. Vector-only control transfections were successful in all four cell lines. Inducible overexpression of bax was achieved in the U87 cells and elevated levels of BAX were observed as early as 6 hours after gene induction. This overexpression of BAX resulted in the spontaneous induction of apoptosis in these cells.

CONCLUSIONS

Overexpression of BAX in four human glioma cell lines resulted in increased sensitivity to apoptosis. In the two lines that had a wild-type p53 genotype, overexpression of BAX produced spontaneous apoptosis. In contrast, the lines that had mutant, nonfunctional P53 did not undergo spontaneous apoptosis, but they were rendered more sensitive to the apoptosis-inducing effect of ara-C. Modulation of BAX expression may be a useful therapeutic modality for gliomas, regardless of p53 genotype.

Developmental regulation of apoptosis in dorsal root ganglion neurons

The survival of dorsal root ganglion (DRG) neurons, both in vivo and in vitro, is dependent on the availability of nerve growth factor (NGF) for a transient period early in development after which these neurons become independent of NGF for survival. The precise molecular mechanism by which developing DRG neurons gain independence from NGF has not been determined. We used an in vitro model of DRG neuronal development to test hypotheses that independence from NGF in mature DRG neurons could be caused by developmental regulation of either elements of the NGF withdrawal signal transduction pathway or of proteins important for activation of the apoptosis output pathway. Interruption of phosphotidylinositol-3 kinase activation, by treatment with the specific inhibitor LY294002, resulted in apoptosis in immature but not mature DRG neurons in a manner similar to that observed with NGF withdrawal. Further downstream along the signal transduction pathway, c-JUN phosphorylation occurred in both immature and mature DRG neurons after NGF withdrawal or treatment with LY294002, despite the fact that the older neurons did not undergo apoptosis. In contrast, the ratio of expression of the proapoptotic gene bax to antiapoptotic gene bcl-xL was many times higher in immature than mature neurons, both in vivo and in vitro. Taken together, these results strongly suggest that developmental regulation of NGF withdrawal-induced apoptosis in DRG occurs via control of the relative level of expression of members of the bcl-2 gene family.

Transfection of C6 glioma cells with the bax gene and increased sensitivity to treatment with cytosine arabinoside

OBJECT

Genes known to be involved in the regulation of apoptosis include members of the bcl-2 gene family, such as inhibitors of apoptosis (bcl-2 and bcl-xl) and promoters of apoptosis (bax). The authors investigated a potential approach for the treatment of malignant gliomas by using a gene transfection technique to manipulate the level of an intracellular protein involved in the control of apoptosis.

METHODS

The authors transfected the murine bax gene, which had been cloned into a mammalian expression vector, into the C6 rat glioma cell line. Overexpression of the bax gene resulted in a decreased growth rate (average doubling time of 32.96 hours compared with 22.49 hours for untransfected C6, and 23.11 hours for clones transfected with pcDNA3 only), which may be caused, in part, by an increased rate of spontaneous apoptosis (0.77 +/- 0.15% compared with 0.42 +/- 0.08% for the vector-only transfected C6 cell line; p = 0.038, two-tailed Student's t-test). Treatment with 1 microM cytosine arabinoside (ara-C) resulted in significantly more cells undergoing apoptosis in the cell line overexpressing bax than in the vector-only control cell line (23.57 +/- 2.6% compared with 5.3 +/- 0.7% terminal deoxynucleotidyl transferase-mediated biotinylated-deoxyuridine triphosphate nick-end labeling technique-positive cells; p = 0.007). Furthermore, measurements of growth curves obtained immediately after treatment with 0.5 microM ara-C demonstrated a prolonged growth arrest of at least 6 days in the cell line overexpressing bax.

CONCLUSIONS

These results can be used collectively to argue that overexpression of bax results in increased sensitivity of C6 cells to ara-C and that increasing bax expression may be a useful strategy, in general, for increasing the sensitivity of gliomas to antineoplastic treatments.

Radiation-induced apoptosis in dorsal root ganglion neurons

Ionizing radiation (IR) results in apoptosis in a number of actively proliferating or immature cell types. The effect of IR on rat dorsal root ganglion (DRG) neurons was examined in dissociated cell cultures. After exposure to IR, embryonic DRG neurons, established in cell culture for six days, underwent cell death in a manner that was dose-dependent, requiring a minimum of 8 to 16 Gy. Twenty-five per cent cell loss occurred in embryonic day 15 (E-15) neurons, grown in cell culture for 6 days ('immature'), and then treated with 24 Gy IR. In contrast, only 2% cell loss occurred in E-15 neurons maintained in culture for 21 days ('mature') and then treated with 24 Gy IR. Staining with a fluorescent DNA-binding dye demonstrated clumping of the nuclear chromatin typical of apoptosis. Initiation of the apoptosis occurred within 24 h after exposure to IR. Apoptosis was prevented by inhibition of protein synthesis with cycloheximide. Apoptosis induced by IR occurred more frequently in immature than in mature neurons. Immature DRG neurons have a lower concentration of intracellular calcium ([Ca2+]i) than mature neurons. Elevation of [Ca2+]i by exposure to a high extracellular potassium ion concentration (35 microM) depolarizes the cell membrane with a resultant influx of calcium ions. The activation of programmed cell death after nerve growth factor (NGF) withdrawal is inversely correlated with [Ca2+]i in immature DRG neurons. When treated with high extracellular potassium, these immature neurons were resistant to IR exposure in a manner similar to that observed in mature neurons. These data suggest that [Ca2+]i modulates the apoptotic response of neurons after exposure to IR in a similar manner to that proposed by the "Ca2+ setpoint hypothesis" for control of NGF withdrawal-induced apoptosis.

Peripheral nerve regeneration through silicone chambers in streptozocin-induced diabetic rats

The silicone chamber model was used to evaluate peripheral nerve regeneration (PNR) in streptozocin (STZ)-induced diabetic rats. Diabetic and control animals underwent sciatic nerve transection and silicone chamber implantation establishing gaps of various lengths between the transected nerve ends. In animals with 5 and 10 mm gaps, diabetes was induced in experimental rats 1 week before surgery, and the animals were sacrificed 3 weeks after surgery. In animals with 8 mm gaps, diabetes induction occurred 3 days after surgery, and they were sacrificed after 7 weeks. Diabetic rats with 10 mm gaps demonstrated an impaired ability to form bridging cables, the initial step of regeneration through chambers. Morphometric studies of bridging cables between transected nerve ends demonstrated a significant reduction in the mean endoneurial area in diabetic animals with 5 and 8 mm gaps compared to controls. The number of regenerated myelinated axons in the chamber was significantly decreased in diabetic rats with 8 and 10 mm gaps. The mean myelinated fiber area in the regenerated cables of the diabetic group was significantly decreased with 5 mm gaps and significantly increased with 8 mm gaps compared to controls. Size-frequency histograms of regenerated myelinated fiber areas suggest a delay in the maturation of small caliber axons. Schwann cell migration across 5 mm gaps was examined with S-100 immunohistochemistry. The total distance of Schwann cell migration into cables from both proximal and distal ends was significantly reduced in diabetic animals. Characterization of PNR across gaps through silicone chambers in diabetic rats showed impairment in multiple aspects of the regenerative process, including cable formation, Schwann cell migration, and axonal regeneration.

Diphenylpiperazines enhance regeneration after facial nerve injury

Immature rat facial motoneurons are very sensitive to injury with nearly 80% dying during the first week after axotomy. This motoneuron death is apoptotic, similar to that induced in neurons after tropic factor withdrawal. The diphenylpiperazines, flunarizine and cinnarizine, protect dorsal root ganglion neurons from death after withdrawal of trophic support, i.e., nerve growth factor withdrawal, in vitro. Similarly, the monoamine oxidase inhibitor, deprenyl, promotes survival of facial motoneurons after axotomy. These pharmacological agents were assessed both alone and in combination for their ability to prevent death in non-nerve growth factor dependent CNS motoneurons after facial nerve axotomy in newborn rats. Long-term experiments were done with the diphenylpiperazines to evaluate potential enhancement of regeneration. Facial nerve transection resulted in 78% neuronal loss in the injured compared with the contralateral, uninjured nucleus. Systemic administration of diphenylpiperazines for 1 week after facial nerve transection doubled the number of surviving motoneurons from 23% to 47%. Similar results were obtained with deprenyl. Combinations of diphenylpiperazines and deprenyl provide a similar degree of neuronal protection 1 week after injury as that obtained by either agent alone. We assessed the ability of diphenylpiperazines to protect facial motoneurons from death over a prolonged period and enhance subsequent regeneration. Motor neuron counts in rats treated with diphenylpiperazines for 1 month after injury and assessed 2 months later demonstrated long-term enhancement of neuronal protection with an increase of 45% in the number of horseradish peroxidase-labelled motoneurons. The diphenylpiperazines group had approximately 80% more regenerated myelinated axons in the distal facial nerve than the control group. Thus, diphenylpiperazine treatment during the first month after injury provides long-term protection of non-nerve growth factor dependent CNS motoneurons with subsequent potentiation of long-term facial nerve regeneration.

Flunarizine enhances survival and regeneration of sensory and motor neurons after peripheral nerve injury

The diphenylpiperazine, flunarizine, partially prevents apoptosis after trophic factor deprivation in neural crest-derived neurons. Flunarizine protects dorsal root ganglion neurons (DRG) after nerve growth factor (NGF) withdrawal in vitro and after peripheral nerve injury in newborn rats in vivo. We have further studied the mechanisms of neuronal protection by flunarizine. Oligosomal DNA fragmentation, a hallmark of apoptosis, was significantly decreased by treatment of DRG neurons with flunarizine after NGF deprivation. We examined the effect on survival of the timing of administration of flunarizine to DRG neurons both in vitro and in vivo. Flunarizine effectively rescued dissociated DRG neurons if administered up to six hours after NGF withdrawal. In vivo, flunarizine prevented DRG neuronal death after sciatic axotomy in newborn rats if given soon after injury. Long-term experiments were done to test the ability of flunarizine to protect neurons and enhance regeneration after sciatic nerve injury. Newborn rats were subjected to peripheral nerve injury and administered flunarizine for four weeks; no further treatment was given for an additional 12 weeks. The group treated with flunarizine demonstrated a significantly increased number of DRG and spinal motor neurons that had regenerated axons into the distal sciatic nerve as determined by retrograde labeling with HRR Myelinated axons in the sural nerve in the group treated with flunarizine increased by nearly two-fold compared to control animals. Thus, flunarizine was able to enhance survival and promote long-term regeneration of sensory and motor spinal neurons after peripheral nerve injury.

Intracellular calcium levels influence apoptosis in mature sensory neurons after trophic factor deprivation

Embryonic dorsal root ganglion (DRG) neurons require nerve growth factor (NGF) for survival in vitro. Withdrawal of NGF results in an apoptotic death in these immature DRG neurons. After time in culture, DRG neurons become progressively less dependent upon NGF for survival. Immature embryonic DRG neurons remain highly dependent upon NGF during their first 14 days in cell culture but by Day 21 the majority lose their NGF dependence for survival. During this period of maturation the intracellular calcium concentration ([Ca2+]i) progressively increases from the lower levels found in immature DRG neurons to the higher levels that are characteristic of older or mature DRG neurons. By changing the cell culture medium to one with very low calcium, we were able to lower [Ca2+]i in the mature neurons to levels similar to those found in immature neurons. These mature neurons (e.g., E-15 DRG neurons grown for 21 days in culture), normally NGF independent, became highly dependent upon NGF for survival. The onset of DNA fragmentation is a marker of apoptotic cell death. We measured the onset of DNA fragmentation in apoptotic neurons with use of the fluorescent dye, Hoechst, in neurons maintained in either standard calcium medium (1800 mM) or in the low calcium medium (0.35 mM). A higher percentage of neurons with lowered [Ca2+]i showed initial signs of apoptosis, i.e., DNA condensation, at earlier times after NGF deprivation. This work provides further evidence to support a "set-point" hypothesis regarding the relationship between intracellular calcium concentration and NGF dependence for survival in DRG neurons.