Developmental and aging changes of Bak expression in the human brain

Thymoquinone ameliorates age-related hearing loss in C57BL/6J mice by modulating Sirt1 activity and Bak1 expression

Age-related hearing loss (AHL) is the most common sensory disorder of aged population. Currently, one of the most important sources of experimental medicine for AHL is medicinal plants. This study performed the first investigation of the effect of thymoquinone (TQ), a potent antioxidant, on AHL. Here, we used inbred C57BL/6J mice (B6 mice) as a successful experimental model of the early onset of AHL. The behavioral assessment of hearing revealed that the injection of a high dose of TQ (40 mg/kg; TQ40) significantly improved the auditory sensitivity of B6 mice at all tested frequencies (8, 16 and 22 kHz). Histological sections of cochlea from B6 mice injected with a low dose (20 mg/kg; TQ20) and high dose showed relatively less degenerative signs in the modiolus, hair cells and spiral ligaments, the main constituents of the cochlea. In addition, TQ40 completely restored the normal pattern of hair cells in B6 mice, as shown in scanning electron micrographs. Our data indicated that TQ20 and TQ40 reduced levels of Bak1-mediated apoptosis in the cochlea of B6 mice. Interestingly, the level of Sirt1, a positive regulator of autophagy, was significantly increased in B6 mice administered TQ40. In conclusion, TQ relieves the symptoms of AHL by downregulating Bak1 and activating Sirt1 in the cochlea of B6 mice.

The effect and mechanism of 19S proteasome PSMD11/Rpn6 subunit in D-Galactose induced mimetic aging models

Regulating proteasome activity is a potent therapeutic aspect of age-related hearing loss, which has been proven to protect neurons from age-related damaging. PSMD11, subunit of the 19S proteasome regulatory particle, is known to mainly up-regulate proteasome activity and prolong aging. However, the mechanism of PSMD11 in age-related hearing loss has not been deeply explored. In the present study, we explore the function and mechanism of PSMD11 protecting neurons in d-Galactose (D-Gal) mimetic aging models. Age-related pathologies were detected by Taq-PCR, ABR, Transmission electron microscopy, toluidine blue and β-galactosidase staining. The relative expressions of the proteins were explored by Western blotting, oxyblot, immunoprecipitation and immunofluorescence. Flow cytometry was used to manifest the oxidative state. We discovered that proteasome activity was impaired with aging, and that ROS and toxic protein accumulated in D-Gal induced aging models. PSMD11 changed with aging, and was associated with the metabolism of proteasome activity in the D-Gal treated models. Moreover, the knockdown or overexpression of PSMD11 was sufficient to change the oxidative state caused by D-Gal. Our results also demonstrated that PSMD11 could bond to AMPKα1/2 in the auditory cortex and PC12 cells, and AMPKα2 but not AMPKα1 was efficient to regulate the function of PSMD11. Deeper insights into the mechanisms of regulating PSMD11 for the anti-aging process are needed, and may offer novel therapeutic methods for central presbycusis.

Mitochondrial quality control as a key determinant of cell survival

Mitochondria are the energy producing dynamic double-membraned organelles essential for cellular and organismal survival. A multitude of intra- and extra-cellular signals involved in the regulation of energy metabolism and cell fate determination converge on mitochondria to promote or prevent cell survival by modulating mitochondrial function and structure. Mitochondrial fitness is maintained by mitophagy, a pathway of selective degradation of dysfunctional organelles. Mitophagy impairment and altered clearance results in increased levels of dysfunctional and structurally aberrant mitochondria, changes in energy production, loss of responsiveness to intra- and extra-cellular signals and ultimately cell death. The decline of mitochondrial function and homeostasis with age is reported to be central to age-related pathologies. Here we discuss the molecular mechanisms controlling mitochondrial dynamics, mitophagy and cell death signalling and how their perturbation may contribute to ageing and age-related illness.

Indeterminate body growth and lack of gonadal decline in the brown ghost knifefish (Apteronotus leptorhynchus), an organism exhibiting negligible brain senescence

The brown ghost knifefish (Apteronotus leptorhynchus (Ellis in Eigenmann, 1912)) is the only vertebrate organism identified thus far that exhibits negligible brain senescence. The present study examines the basic growth patterns of this species, testing the hypothesis that indeterminate growth and lack of reproductive senescence correlate with negligible senescence. Analysis of length–mass relationships revealed negative allometric growth in males and isometric growth in females. Total length at first sexual maturity was 13.5 cm in males and 12.0 cm in females, whereas gonadal mass was 0.02 g in males and 0.2 g in females. Modelling of total length as a function of the number of otolith rings using attenuating growth equations revealed that lengths of up to 26.8 cm in males and 20.2 cm in females can be reached, indicating that the fish continue to grow throughout life. Gonadal mass increased significantly with age in sexually immature individuals of both sexes. In sexually mature fish, gonadal mass showed a marginal increase with age in males and no change in females. The demonstration of indeterminate growth of the fish and of the lack of gonadal regression with age has important implications for the characterization of brown ghost knifefish as a model of negligible senescence.

Age-related changes in stem cell dynamics, neurogenesis, apoptosis, and gliosis in the adult brain: a novel teleost fish model of negligible senescence

Adult neurogenesis, the generation of new neurons in the adult central nervous system, is a reported feature of all examined vertebrate species. However, a dramatic decline in the rates of cell proliferation and neuronal differentiation occurs in mammals, typically starting near the onset of sexual maturation. In the present study, we examined possible age-related changes associated with adult neurogenesis in the brain of brown ghost knifefish (Apteronotus leptorhynchus), a teleost fish distinguished by its enormous neurogenic potential. Contrary to the well-established alterations in the mammalian brain during aging, in the brain of this teleostean species we could not find evidence for any significant age-related decline in the absolute levels of stem/progenitor cell proliferation, neuronal and glial differentiation, or long-term survival of newly generated cells. Moreover, there was no indication that the amount of glial fibrillary acidic protein or the number of apoptotic cells in the brain was altered significantly over the course of adult life. We hypothesize that this first demonstration of negligible cellular senescence in the vertebrate brain is related to the continued growth of this species and to the lack of reproductive senescence during adulthood. The establishment of the adult brain of this species as a novel model of negligible senescence provides new opportunities for the advancement of our understanding of the biology of aging and the fundamental mechanisms that underlie senescence in the brain.

Defining the role of the Bcl-2 family proteins in Huntington's disease

B-cell lymphoma 2 (Bcl-2) family proteins regulate survival, mitochondria morphology dynamics and metabolism in many cell types including neurons. Huntington's disease (HD) is a neurodegenerative disorder caused by an expanded CAG repeat tract in the IT15 gene that encodes for the protein huntingtin (htt). In vitro and in vivo models of HD and HD patients' tissues show abnormal mitochondrial function and increased cell death rates associated with alterations in Bcl-2 family protein expression and localization. This review aims to draw together the information related to Bcl-2 family protein alterations in HD to decipher their potential role in mutated htt-related cell death and mitochondrial dysfunction.

Mitochondrial oxidative damage and apoptosis in age-related hearing loss

Age-related hearing loss (AHL) is a universal feature of mammalian aging and is the most common sensory disorder in the elderly population. Experimental evidence suggests that mitochondrial dysfunction associated with reactive oxygen species (ROS) plays a central role in the aging process of cochlear cells. Although it is well established that mitochondria are the major source of ROS in the cell, specific molecular mechanisms of aging induced by ROS remain poorly characterized. Here we review the evidence that supports a central role for Bak-mediated mitochondrial apoptosis in AHL. We also propose that this mechanism may be of general relevance to age-related cell death in long-lived post-mitotic cells of multiple tissues, providing an opportunity for a targeted therapeutic intervention in human aging.

Age-related hearing loss in C57BL/6J mice is mediated by Bak-dependent mitochondrial apoptosis

Age-related hearing loss (AHL), known as presbycusis, is a universal feature of mammalian aging and is the most common sensory disorder in the elderly population. The molecular mechanisms underlying AHL are unknown, and currently there is no treatment for the disorder. Here we report that C57BL/6J mice with a deletion of the mitochondrial pro-apoptotic gene Bak exhibit reduced age-related apoptotic cell death of spiral ganglion neurons and hair cells in the cochlea, and prevention of AHL. Oxidative stress induces Bak expression in primary cochlear cells, and Bak deficiency prevents apoptotic cell death. Furthermore, a mitochondrially targeted catalase transgene suppresses Bak expression in the cochlea, reduces cochlear cell death, and prevents AHL. Oral supplementation with the mitochondrial antioxidants alpha-lipoic acid and coenzyme Q(10) also suppresses Bak expression in the cochlea, reduces cochlear cell death, and prevents AHL. Thus, induction of a Bak-dependent mitochondrial apoptosis program in response to oxidative stress is a key mechanism of AHL in C57BL/6J mice.

Therapeutic potential of BAK gene silencing in aluminum induced neural cell degeneration

Previous studies have demonstrated robust BAK gene silencing via RNA interference (RNAi). To investigate whether BAK RNAi may serve as a co-therapeutic agent in neural cell death, we herein established a cell degeneration model using a human neuroblastoma cell line (SH-SY5Y) treated by aluminum (Al). Combining cell viability assays and expression analyses by QRT (quantitative real-time)-PCR and immunocytochemistry, we selected and validated the optimal small interfering RNA (siRNA) from three candidate siRNAs for the BAK gene. Our data identified siRNA1 as the most effective siRNA; the optimal concentration of the transfection agent was 10nM and the optimal incubation period was 24h. The transfection and knockdown efficiency was 93% and 58%, respectively, which closely correlated with the BAK protein expression. SH-SY5Y cells with BAK knockdown showed a clear resistance against cell death and Al-induced apoptosis. These results indicate that genetic inactivation of BAK could be an effective strategy in delaying the onset of apoptosis in Al-treated cells, and exemplify the therapeutic potential of RNAi-based methods for the treatment of neural cell degeneration.

Cell death in the Purkinje cells of the cerebellum of senescence accelerated mouse (SAMP(8))

The cerebella of SAMP(8) (accelerated aging mouse) and SAMR(1) controls were analyzed by Western Blotting of tyrosine hydroxylase and choline acetyltransferase, as well as by TUNEL and histological silver staining. Both tyrosine hydroxylase and choline acetyltransferase levels were higher in SAMR(1) than in SAMP(8). There was also an age-related decrease in enzyme levels in SAMP(8), with the reduction of tyrosine hydroxylase being more apparent. Concomitantly, there was an age-related increase of apoptosis in the medial neocerebellum and the vermis as revealed by TUNEL, with changes being significant in the SAMP(8) strain. Histologically, some Purkinje cells appeared to disappear during aging. Taken together, the data suggests that the aging SAMP(8) strain displays differential Purkinje cell death in the medial cerebellum and that some of the dying cells are likely to be catecholaminergic.

The X-Ray Structure of a BAK Homodimer Reveals an Inhibitory Zinc Binding Site

BAK/BAX-mediated mitochondrial outer-membrane permeabilization (MOMP) drives cell death during development and tissue homeostasis from zebrafish to humans. In most cancers, this pathway is inhibited by BCL-2 family antiapoptotic members, which bind and block the action of proapoptotic BCL proteins. We report the 1.5 A crystal structure of calpain-proteolysed BAK, cBAK, to reveal a zinc binding site that regulates its activity via homodimerization. cBAK contains an occluded BH3 peptide binding pocket that binds a BID BH3 peptide only weakly . Nonetheless, cBAK requires activation by truncated BID to induce cytochrome c release in mitochondria isolated from bak/bax double-knockout mouse embryonic fibroblasts. The BAK-mediated MOMP is inhibited by low micromolar zinc levels. This inhibition is alleviated by mutation of the zinc-coordination site in BAK. Our results link directly the antiapoptotic effects of zinc to BAK.

Apoptosis in stress-induced and spontaneously senescent human fibroblasts

Although apoptosis has been shown in vivo to be involved in the aging process, in vitro studies of age-dependent apoptosis are limited. In this study, apoptosis was examined in normal human fibroblasts exposed to H(2)O(2) to induce premature senescence and in spontaneously senescent human fibroblasts. Although apoptosis was not observed for several days after exposure to H(2)O(2), morphological changes indicating apoptosis were evident in about 5% of cells 7 days after exposure to 80microM H(2)O(2), concomitantly with expression of senescent phenotype. The apoptotic changes were preceded by caspase activation in majority of the exposed cells. As well as H(2)O(2)-induced senescent cells, spontaneously senescent human fibroblasts showed apoptotic changes in about 2% of cells and majority of the senescent cells also showed activation of caspases. The results indicate that the apoptosis pathway is activated in H(2)O(2)-induced and spontaneously senescent human fibroblasts in vitro.

Possible involvement of a fibroblast growth factor 9 (FGF9)-FGF receptor-3-mediated pathway in adult pig retinal ganglion cell survival in vitro

The expression and potential roles of fibroblast growth factors (FGF) and their cognate FGF receptors (FGFR) in adult mammalian retinal ganglion cells (RGC) are poorly known. We show that FGFR-3 and FGFR-4 are especially pronounced on RGC and amacrine cell bodies in adult pig inner retinae both in vivo and in vitro. Western blotting revealed distinct profiles for each receptor. Expression of each FGFR and effects of the preferred ligand for FGFR-3, FGF9, upon RGC survival and neurite outgrowth were examined in primary retinal cell cultures: whereas there was no stimulation of neuritogenesis, RGC survival was promoted in a dose-dependent manner (ED(50) approximately 500 pg/ml, mean maximal increase of 60%) and could be completely blocked by addition of FGF9 neutralising antibody. Experiments with three additional FGF (FGF1, FGF2, and FGF4) showed no stimulation of RGC survival above control levels. Taken together, these data suggest that the ligand-receptor couple FGF9-FGFR-3 may function to promote survival of adult mammalian RGC, and their application might be beneficial in retinal degenerative diseases such as glaucoma.

Impact of aging and life-long calorie restriction on expression of apoptosis-related genes in male F344 rat liver

Aging enhances apoptosis of hepatocytes under normal physiological conditions and increases the susceptibility to apoptosis of hepatocytes, whereas chronic calorie restriction (CR) suppresses the age-enhanced susceptibility to apoptosis. To clarify the subcellular mechanisms of age-associated dysregulation of apoptosis and the effects of CR, we analyzed the expression of genes promoting apoptosis (p53, Fas receptor, Fas ligand, TNF receptor 1, TNFalpha, Bax, TGF beta 1) and genes preventing apoptosis (Bcl-2 and Bcl-XL) in the livers of 3-, 6-, 15-, and 24-month-old male F344 rats that were either fed ad libitum or subjected to a 30% reduction in food intake (CR). After the age of 6 months, expression of p53, Fas receptor, Fas ligand, and TNFalpha mRNAs was up-regulated with aging. CR suppressed this age-enhanced p53 and Fas receptor mRNA expression, but expression of the other genes was not altered significantly by aging or CR. Expression of Fas receptor in hepatocytes, as detected immunohistochemically, increased with age, but CR suppressed age-accelerated Fas receptor expression. Our findings suggest that TNF ligand/TNF receptor family signaling, particularly Fas receptor expression, is important in age- and CR-modulated apoptosis of hepatocytes. Hepatocytes that were immunoreactive for p53 had slightly increased with aging, suggesting that p53 may mediate the age-enhanced up-regulation of Fas receptor in hepatocytes.

Evidence for apoptosis in the fetal Down syndrome brain

In Down syndrome, enhanced apoptosis (programmed cell death) may play a role in the pathogenesis of characteristic early mental retardation and precocious neurodegeneration of Alzheimer type. Various apoptosis-associated proteins (Bax, Bcl-2, Fas, p53, Hsp70, neuronal apoptosis inhibitory protein-like immunoreactivity) were investigated in four different cortical regions and the cerebellum of one fetal Down syndrome (35 weeks' gestation) postmortem brain sample compared with a control brain sample. The most impressive finding was an at least fivefold elevation of Bax protein together with decreased Bcl-2 values in all Down syndrome cerebral regions investigated. In addition, antiapoptotic, presumably caspase-inhibitory, principles like heat shock protein 70 and neuronal apoptosis inhibitory protein were also reduced. Whereas Fas protein, an important member of receptor-mediated apoptosis, was inconsistently altered, a rather surprising finding was reduced proapoptotic, regulatory protein p53 in four of five regions. The findings are in good agreement with the proposed role of the Bcl-2 protein family in regulating developmental (naturally occurring) apoptotic neuronal death and further suggest that developmental apoptosis may be inappropriately commandeered by so far undefined pathologic processes in Down syndrome.

Proteasomes modulate balance among proapoptotic and antiapoptotic Bcl-2 family members and compromise functioning of the electron transport chain in leukemic cells

The mechanism underlying apoptosis induced by proteasome inhibition in leukemic Jurkat and Namalwa cells was investigated in this study. The proteasome inhibitor lactacystin differentially regulated the protein levels of proapoptotic Bcl-2 family members and Bik was accumulated at the mitochondria. Bik overexpression sufficed to induce apoptosis in these cells. Detailed examination along the respiration chain showed that lactacystin compromised a step after complex III, and exogenous cytochrome c could overcome this compromise. Probably as a result, the succinate-stimulated generation of mitochondrial membrane potential was significantly diminished. Bcl-x(L) interacted with Bik in the cells, and Bcl-x(L) overexpression prevented cytochrome c leakage out of the mitochondria, corrected the mitochondrial membrane potential defect, and protected the cells from apoptosis. These results show that proteasomes can modulate apoptosis of lymphocytes by affecting the half-life of Bcl-2 family members, Bik being one of them.

Differential expression of rat brain bcl-2 family proteins in development and aging

We have previously examined the involvement of the B cell leukemia-2 gene product (Bcl-2) family proteins (Bcl-2, Bcl-x, Bax, Bak, and Bad) in Alzheimer's disease (AD) and found that Bcl-2, Bcl-x, Bak, and Bad were upregulated. As AD is an aging-associated disease, in the present study we examined the developmental and aging-related changes in Bcl-2 family proteins in the rat brain. Immunoblot analyses of brain extracts from embryonic day 19 (E19) to postnatal 96-week-old rats indicated that the Bcl-2 protein level was highest at E19 and decreased after birth. Bcl-x levels remained high from E19 to 96 weeks. Bax levels were high from E19 to 2 weeks and decreased from 4 weeks onward. Bak levels were highest at E19 and decreased abruptly after birth. Bad levels were high from E19 to 2 weeks and decreased abruptly at 4 weeks. The present results suggest that the expression of each Bcl-2 family protein is differentially regulated during development and aging and that the changes in the senescent brains are different from those observed in AD.