Restoration of mitochondrial function reverses developmental neuronal death in vitro

Hypoxic regulation of osteoclast differentiation and bone resorption activity

Bone integrity is maintained throughout life via the homeostatic actions of bone cells, namely, osteoclasts, which resorb bone, and osteoblasts, which produce bone. Disruption of this balance in favor of osteoclast activation results in pathological bone loss, which occurs in conditions including osteoporosis, rheumatoid arthritis, primary bone cancer, and cancer metastasis to bone. Hypoxia also plays a major role in these conditions, where it is associated with disease progression and poor prognosis. In recent years, considerable interest has arisen in the mechanisms whereby hypoxia and the hypoxia-inducible transcription factors, HIF-1α and HIF-2α, affect bone remodeling and bone pathologies. This review summarizes the current evidence for hypoxia-mediated regulation of osteoclast differentiation and bone resorption activity. Role(s) of HIF and HIF target genes in the formation of multinucleated osteoclasts from cells of the monocyte-macrophage lineage and in the activation of bone resorption by mature osteoclasts will be discussed. Specific attention will be paid to hypoxic metabolism and generation of ATP by osteoclasts. Hypoxia-driven increases in both glycolytic flux and mitochondrial metabolic activity, along with consequent generation of mitochondrial reactive oxygen species, have been found to be essential for osteoclast formation and resorption activity. Finally, evidence for the use of HIF inhibitors as potential therapeutic agents targeting bone resorption in osteolytic disease will be discussed.

Protective effects of zonisamide against rotenone-induced neurotoxicity

Zonisamide (ZNS), an antiepileptic drug having beneficial effects also against Parkinson's disease symptoms, has proven to display an antioxidant effects in different experimental models. In the present study, the effects of ZNS on rotenone-induced cell injury were investigated in human neuroblastoma SH-SY5Y cells differentiated towards a neuronal phenotype. Cell cultures were exposed for 24 h to 500 nM rotenone with or without pre-treatment with 10-100 μM ZNS. Then, the following parameters were analyzed: (a) cell viability; (b) intracellular reactive oxygen species production; (c) mitochondrial transmembrane potential; (d) cell necrosis and apoptosis; (e) caspase-3 activity. ZNS dose-dependently suppressed rotenone-induced cell damage through a decrease in intracellular ROS production, and restoring mitochondrial membrane potential. Similarly to ZNS effects, the treatment with N-acetyl-cysteine (100 μM) displayed significant protective effects against rotenone-induced ROS production and Δψm at 4 and 12 h respectively, reaching the maximal extent at 24 h. Additionally, ZNS displayed antiapoptotic effects, as demonstrated by flow cytometric analysis of annexin V/propidium iodide double staining, and significant attenuated rotenone-increased caspase 3 activity. On the whole, these findings suggest that ZNS preserves mitochondrial functions and counteracts apoptotic signalling mechanisms mainly by an antioxidant action. Thus, ZNS might have beneficial effect against neuronal cell degeneration in different experimental models involving mitochondrial dysfunction.

Acute hypoxia and osteoclast activity: a balance between enhanced resorption and increased apoptosis

Osteoclasts are the primary mediators of pathological bone resorption in many conditions in which micro-environmental hypoxia is associated with disease progression. However, effects of hypoxia on human osteoclast activity have not been reported. Mature human osteoclasts were differentiated from peripheral blood or obtained from giant cell tumour of bone. Osteoclasts were exposed to a constant hypoxic environment and then assessed for parameters including resorption (toluidine blue staining of dentine slices), membrane integrity (trypan blue exclusion), apoptosis (TUNEL, DAPI), and osteolysis-associated enzyme activity (TRAP, cathepsin K). 24 h exposure to 2% O(2) produced a 2.5-fold increase in resorption associated with increased TRAP and cathepsin K enzyme activity. Hypoxia-Inducible Factor-1alpha (HIF-1alpha) siRNA completely ablated the hypoxic increase in osteoclast resorption. 24 h at 2% O(2) also increased the number of osteoclasts with compromised membrane integrity from 6% to 21%, with no change in the total osteoclast number or the proportion of late-stage apoptotic cells. Transient reoxygenation returned the percentage of trypan blue-positive cells to normoxic levels, suggesting that osteoclasts can recover from the early stages of cell death. Repeated over an extended period, hypoxia/reoxygenation enhanced osteoclast differentiation at this pO(2). These data suggest that in diseased bone, where the pO(2) may fall to <or=2% O(2), a delicate balance between hypoxia-induced osteoclast activation and hypoxia-induced osteoclast apoptosis mediates pathological bone resorption.

Activation of apoptotic pathways at muscle fiber synapses is circumscribed and reversible in a slow-channel syndrome model

In the slow-channel syndrome (SCS) mutant acetylcholine receptors elicit calcium overload and myonuclear degeneration at the neuromuscular junction (NMJ), without muscle fiber death. Activated caspases are present at SCS motor endplates. We hypothesized that SCS represents a limited form of apoptosis. We found condensed chromatin and occasional single-strand DNA nicks in degenerating synaptic nuclei. Cleaved forms of caspases-3 and -9 were present in mouse SCS muscle homogenates and were specifically localized to NMJs. Finally, interruption of cholinergic activity by axotomy markedly reduced NMJ caspase activity and improved the morphological features of apoptosis at NMJs. These results demonstrate that in SCS processes leading to apoptosis may remain compartmentalized and reversible. Use of cysteine protease inhibitors may aid in treatment of this and other dystrophic muscle and excitotoxic disorders. Identification of extrasynaptic factors that prevent the spread of apoptosis in SCS muscle fibers may aid in developing treatments for neurological disorders characterized by excitotoxicity or apoptosis.

Toxic epidermal necrolysis: current evidence, practical management and future directions

Toxic epidermal necrolysis (TEN) is a rare disorder characterized by extensive epidermal death. Almost all cases appear to be caused by an idiosyncratic drug reaction. Proposed pathogenic mechanisms are conflicting, and the evidence for the benefits of individual treatments is inadequate, and in some cases contradictory. The mortality rate remains high. We review the literature pertaining to the pathogenesis of TEN and drug reactions in general. The rationale for therapeutic interventions, together with reported evidence of efficacy, are considered. We present a composite model of TEN, based on previous work and suggested pathogeneses of TEN, mechanisms of drug reactions and reported cytotoxic lymphocyte (CTL) cytolytic pathways. In this system, TEN, like some other cutaneous drug eruptions, is an HLA class I-restricted, specific drug sensitivity, resulting in clonal expansion of CD8+ CTLs. Cytotoxicity is mediated by CTL granzyme and possibly death receptor (DR) ligand (DR-L), probably Fas ligand (FasL). Particular to TEN, there is then an amplification sequence involving further DR-L expression. FasL is likely to be particularly important but tumour necrosis factor (TNF) may well contribute, via the TNF receptor 1 (TNF-R1) death pathway. Alternatively, we suggest the possibility of upregulation of an antiapoptotic TNF-R1-nuclear factor kappaB pathway, which would proscribe treatments which downregulate this pathway. None of the published data on individual treatment efficacies is sufficiently strong to suggest a definitive single treatment. Currently a multifaceted regimen appears indicated, targeting various likely intermediary mechanisms, including elimination of residual drug, immunosuppression, inhibition of DR pathways, general antiapoptotic strategies, and aggressive supportive care. Particular attention has been directed at avoiding potential conflicts between different treatments and avoiding agents that theoretically might have a net proapoptotic rather than antiapoptotic effect. Nursing on a specialized unit is of paramount importance.

Ultrastructure of retinal ganglion cell death after axotomy in chick embryos

Axotomy often leads to neuronal death, which occurs after a particularly short delay in immature animals. Tectal lesions were made in embryonic day (E) 12 chick embryos, thereby axotomizing the retinal ganglion cells of the contralateral eye, which then died within 3 days. We here describe the ultrastructural changes in the axotomized ganglion cells. The main changes were nuclear invagination and type 3B (cytoplasmic type) cell death characterized by dilation of the perinuclear space, endoplasmic reticulum, and Golgi apparatus. However, nuclear invagination was never seen in type 3B dying cells. All the axotomy-induced retinal ganglion cell death appears to have been of type 3B; apoptosis was not induced by axotomy, as was confirmed by additional light microscopic experiments showing that it did not increase the frequency of apoptotic markers revealed by terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (the TUNEL method) labeling and immunoreactivity for activated caspase-3. However, the latter methods did show small numbers of apoptotic cells dying naturally even in control retinas. After the death of the axotomized ganglion cells, they were phagocytosed mainly in Müller processes. The present findings open up the chick tectal lesion model as a system for analyzing type 3B neuronal death in vivo.