Background: Aberrant biometal metabolism is a key feature of neurodegenerative disorders including Alzheimer's and Parkinson's diseases. Metal modulating compounds are promising therapeutics for neurodegeneration, but their mechanism of action remains poorly understood. Neuronal ceroid lipofuscinoses (NCLs), caused by mutations in CLN genes, are fatal childhood neurodegenerative lysosomal storage diseases without a cure. We previously showed biometal accumulation in ovine and murine models of the CLN6 variant NCL, but the mechanism is unknown. This study extended the concept that alteration of biometal functions is involved in pathology in these disorders, and investigated molecular mechanisms underlying impaired biometal trafficking in CLN6 disease.Results: We observed significant region-specific biometal accumulation and deregulation of metal trafficking pathways prior to disease onset in CLN6 affected sheep. Substantial progressive loss of the ER/Golgi-resident Zn transporter, Zip7, which colocalized with the disease-associated protein, CLN6, may contribute to the subcellular deregulation of biometal homeostasis in NCLs. Importantly, the metal-complex, ZnII(atsm), induced Zip7 upregulation, promoted Zn redistribution and restored Zn-dependent functions in primary mouse Cln6 deficient neurons and astrocytes.Conclusions: This study demonstrates the central role of the metal transporter, Zip7, in the aberrant biometal metabolism of CLN6 variants of NCL and further highlights the key contribution of deregulated biometal trafficking to the pathology of neurodegenerative diseases. Importantly, our results suggest that ZnII(atsm) may be a candidate for therapeutic trials for NCLs.

Abnormal processing of TAR DNA binding protein 43 (TDP-43) has been identified as a major factor in neuronal degeneration during amyotrophic lateral sclerosis (ALS) or frontotemporal lobar degeneration (FTLD). It is unclear how changes to TDP-43, including nuclear to cytosolic translocation and subsequent accumulation, are controlled in these diseases. TDP-43 is a member of the heterogeneous ribonucleoprotein (hnRNP) RNA binding protein family and is known to associate with cytosolic RNA stress granule proteins in ALS and FTLD. hnRNP trafficking and accumulation is controlled by the action of specific kinases including members of the mitogen-activated protein kinase (MAPK) pathway. However, little is known about how kinase pathways control TDP-43 movement and accumulation. In this study, we used an in vitro model of TDP-43-positve stress granule formation to screen for the effect of kinase inhibitors on TDP-43 accumulation. We found that while a number of kinase inhibitors, particularly of the MAPK pathways modulated both TDP-43 and the global stress granule marker, human antigen R (HuR), multiple inhibitors were more specific to TDP-43 accumulation, including inhibitors of cyclin-dependent kinases (CDKs) and glycogen synthase kinase 3 (GSK3). Close correlation was observed between effects of these inhibitors on TDP-43, hnRNP K and TIAR, but often with different effects on HuR accumulation. This may indicate a potential interaction between TDP-43, hnRNP K and TIAR. CDK inhibitors were also found to reverse pre-formed TDP-43-positive stress granules and both CDK and GSK3 inhibitors abrogated the accumulation of C-terminal TDP-43 (219-414) in transfected cells. Further studies are required to confirm the specific kinases involved and whether their action is through phosphorylation of the TDP-43 binding partner hnRNP K. This knowledge provides a valuable insight into the mechanisms controlling abnormal cytoplasmic TDP-43 accumulation and may herald new opportunities for kinase modulation-based therapeutic intervention in ALS and FTLD.

Copper (Cu) is an essential biometal involved in a number of cell functions. Abnormal Cu homeostasis has been identified as a major factor in a number of neurodegenerative disorders. However, little is known about how cells of brain origin maintain Cu homeostasis and in particular, how they respond to an elevated Cu environment. Understanding these processes is essential to obtaining a greater insight into the pathological changes in neurodegeneration and ageing. Although previous studies have shown that Cu in neurons can be associated with synaptic function, there is little understanding of how Cu modulates the regulated secretory vesicle pathways in these cells. In this study, we examined the effect of elevated intracellular Cu on proteins associated with the regulated secretory vesicle pathway in NGF-differentiated PC12 cells that exhibit neuronal-like properties. Increasing intracellular Cu with a cell-permeable Cu-complex (Cu(II)(gtsm)) resulted in increased expression of synaptophysin and robust translocation of this and additional vesicular proteins from synaptic-like microvesicle (SLMV) fractions to chromogranin-containing putative large dense core vesicle (LDCV) fractions in density gradient preparations. The LDCV fractions also contained substantially elevated Cu levels upon treatment of cells with Cu(II)(gtsm). Expression of the H(+) pump, V-ATPase, which is essential for vesicle maturation, was increased in Cu-treated cells while inhibition of V-ATPase prevented translocation of synaptophysin to LDCV fractions. Cu treatment was found to inhibit release of LDCVs in chromaffin cells due to reduced Ca(2+)-mediated vesicle exocytosis. Our findings demonstrate that elevated Cu can modulate LDCV metabolism potentially resulting in sequestration of Cu in this vesicle pool.

Mutations in the CLN6 gene cause a variant late infantile form of neuronal ceroid lipofuscinosis (NCL; Batten disease). CLN6 loss leads to disease clinically characterized by vision impairment, motor and cognitive dysfunction, and seizures. Accumulating evidence suggests that alterations in metal homeostasis and cellular signaling pathways are implicated in several neurodegenerative and developmental disorders, yet little is known about their role in the NCLs. To explore the disease mechanisms of CLN6 NCL, metal concentrations and expression of proteins implicated in cellular signaling pathways were assessed in brain tissue from South Hampshire and Merino CLN6 sheep. Analyses revealed increased zinc and manganese concentrations in affected sheep brain in those regions where neuroinflammation and neurodegeneration first occur. Synaptic proteins, the metal-binding protein metallothionein, and the Akt/GSK3 and ERK/MAPK cellular signaling pathways were also altered. These results demonstrate that altered metal concentrations, synaptic protein changes, and aberrant modulation of cellular signaling pathways are characteristic features in the CLN6 ovine form of NCL.

TDP-43 proteinopathies are characterized by loss of nuclear TDP-43 and accumulation of the protein in the cytosol as ubiquitinated protein aggregates. These protein aggregates may have an important role in subsequent neuronal degeneration in motor neuron disease, frontotemporal dementia and potentially other neurodegenerative diseases. Although the cellular mechanisms driving the abnormal accumulation of TDP-43 are not understood, recent studies have shown that an early change to TDP-43 metabolism in disease may be accumulation in cytosolic RNA stress granules (SGs). However, it is unclear whether the TDP-43 in these SGs progresses to become irreversible protein aggregates as observed in patients. We have shown recently that paraquat-treated cells are a useful model for examining TDP-43 SG localization. In this study, we used the paraquat model to examine if endogenous TDP-43 in SGs can progress to more stable protein aggregates. We found that after treatment of HeLa cells overnight with paraquat, TDP-43 co-localized to SGs together with the ubiquitous SG marker, human antigen R (HuR). However, after a further incubation in paraquat-free, conditioned medium for 6h, HuR-positive SGs were rarely detected yet TDP-43 positive aggregates remained present. The majority of these TDP-43 aggregates were positive for ubiquitin. Further evidence for persistence of TDP-43 aggregates was obtained by treating cultures with cycloheximide after paraquat treatment. Cycloheximide abolished nearly all cytosolic HuR aggregation (SGs) but large TDP-43-positive aggregates remained. Finally, we showed that addition of ERK and JNK inhibitors together with paraquat blocked TDP-43-positive SG formation, while treatment with inhibitors after 24h paraquat exposure failed to reverse the TDP-43 accumulation. This failure was most likely due to the addition of inhibitors after maximal activation of the kinases at 4h post-paraquat treatment. These findings provide strong evidence that once endogenous TDP-43 accumulates in SGs, it has the potential to progress to stable protein aggregates as observed in neurons in TDP-43 proteinopathies. This may provide a therapeutic opportunity to inhibit the transition of TDP-43 from SG protein to aggregate.

Amyotrophic lateral sclerosis (ALS) is a progressive, fatal, motor neuron disease with no effective long-term treatment options. Recently, TDP-43 has been identified as a key protein in the pathogenesis of some cases of ALS. Although the role of TDP-43 in motor neuron degeneration is not yet known, TDP-43 has been shown to accumulate in RNA stress granules (SGs) in cell models and in spinal cord tissue from ALS patients. The SG association may be an early pathological change to TDP-43 metabolism and as such a potential target for therapeutic intervention. Accumulation of TDP-43 in SGs induced by inhibition of mitochondrial activity can be inhibited by modulation of cellular kinase activity. We have also found that treatment of cells and animal models of neurodegeneration, including an ALS model, with bioavailable bis(thiosemicarbazonato)copper(II) complexes (Cu-II(btsc)s) can modulate kinase activity and induce neuroprotective effects. In this study we examined the effect of diacetylbis(-methylthiosemicarbazonato)copper(II) (Cu-II(atsm)) and glyoxalbis(-methylthiosemicarbazonato)copper(II) (Cu-II(gtsm)) on TDP-43-positive SGs induced in SH-SY5Y cells in culture. We found that the Cu-II(btsc)s blocked formation of TDP-43-and human antigen R (HuR)-positive SGs induced by paraquat. The Cu-II(btsc) s protected neurons from paraquat-mediated cell death. These effects were associated with inhibition of ERK phosphorylation. Co-treatment of cultures with either Cu-II(atsm) or an ERK inhibitor, PD98059 both prevented ERK activation and blocked formation of TDP-43-and HuR-positive SGs. Cu-II(atsm) treatment or ERK inhibition also prevented abnormal ubiquitin accumulation in paraquat-treated cells suggesting a link between prolonged ERK activation and abnormal ubiquitin metabolism in paraquat stress and inhibition by Cu. Moreover, Cu-II(atsm) reduced accumulation of C-terminal (219-414) TDP-43 in transfected SH-SY5Y cells. These results demonstrate that Cu-II(btsc) complexes could potentially be developed as a neuroprotective agent to modulate neuronal kinase function and inhibit TDP-43 aggregation. Further studies in TDP-43 animal models are warranted.

Copper (Cu) has a critical role in the generation of oxidative stress during neurodegeneration and cancer. Reactive oxygen species generated through abnormal elevation or deficiency of Cu can lead to lipid, protein, and DNA damage. Oxidation of DNA can induce strand breaks and is associated with altered cell fate including transformation or death. DNA repair is mediated through the action of the multimeric DNA–PK repair complex. The components of this complex are the Ku autoantigens, XRCC5 and XRCC6 (Ku80 and Ku70, respectively). How this repair complex responds to perturbed Cu homeostasis and Cu-mediated oxidative stress has not been investigated. We previously reported that XRCC5 expression is altered in response to cellular Cu levels, with low Cu inhibiting XRCC5 expression and high Cu levels enhancing expression. In this study we further investigated the interaction between XRCC5 and Cu. We report that cytosolic XRCC5 is increased in response to Cu, but not zinc, iron, or nickel, and the level of cytosolic XRCC5 correlates with protection against oxidative damage to DNA. These observations were made in both HeLa cells and fibroblasts. Cytosolic XRCC5 interacted with the Cu chaperone and detoxification protein human Atox1 homologue (HAH), and down regulation of XRCC5 expression using siRNA led to enhanced HAH expression when cells were exposed to Cu. XRCC5 could also be purified from cytosolic extracts using a Cu-loaded column. These findings provide further evidence that cytosolic XRCC5 has a key role in protection against DNA oxidation from Cu, through either direct sequestration or signaling through other Cu-detoxification molecules. Our findings have important implications for the development of therapeutic treatments targeting Cu in neurodegeneration and/or cancer.

Brain tumors such as neuroblastomas and gliomas are often refractory to current treatments. Development of metal-based drugs may offer an alternative approach due to the ability to deliver radionuclides or cytotoxic metals to the tumor. Previous studies have shown that diacetyl-bis(N(4)-methylthiosemicarbazonato)-copper(II) (Cu(II)(atsm)) can selectively target hypoxic tumors and this feature has been utilized for development of imaging and radiotherapy. However, we have recently shown that glyoxal-bis(N(4)-methylthiosemicarbazonato)-copper(II) (Cu(II)(gtsm)) can target the brain in animal models of neurodegeneration. Unlike Cu(II)(atsm), Cu(II)(gtsm) is able to release Cu intracellularly under normoxic conditions. Glyoxal-bis(thiosemicarbazones) have reported anticancer effects but little is known about the cellular mechanisms involved. Therefore, in this study, we used protein microarray analysis to investigate the effect of Cu(II)(gtsm) on neuroblastoma cell growth in vitro. Treatment of the human neuroblastoma cell line BE(2)-M17, resulted in cell cycle arrest as assessed by fluorescent activated cell sorting (FACS) analysis. Rapidly arrested growth was not associated with onset of apoptosis. Instead, protein microarray analysis revealed that Cu(II)(gtsm) rapidly and potently reduced cyclin D1 expression, while increasing Kip2 expression. Other changes observed were decreased Cdk7 expression and activation of CHK2. These changes may be associated with the cell cycle arrest. We also observed a potent decrease of total and phosphorylated insulin-like growth factor receptor (IGF-IR) by Cu(II)(gtsm) which is associated with modulation of cyclin D1 expression. Our studies reveal important insights into the potential anticancer activity of Cu(II)(gtsm). Further studies are needed to examine the therapeutic potential of Cu(II)(gtsm) and other bis(thiosemicarbazonato) metal complexes as metallo-drugs for treatment of systemic or brain tumors.

Background TDP-43 proteinopathies are characterized by loss of nuclear TDP-43 expression and formation of C-terminal TDP-43 fragmentation and accumulation in the cytoplasm. Recent studies have shown that TDP-43 can accumulate in RNA stress granules (SGs) in response to cell stresses and this could be associated with subsequent formation of TDP-43 ubiquinated protein aggregates. However, the initial mechanisms controlling endogenous TDP-43 accumulation in SGs during chronic disease are not understood. In this study we investigated the mechanism of TDP-43 processing and accumulation in SGs in SH-SY5Y neuronal-like cells exposed to chronic oxidative stress. Cell cultures were treated overnight with the mitochondrial inhibitor paraquat and examined for TDP-43 and SG processing. Results We found that mild stress induced by paraquat led to formation of TDP-43 and HuR-positive SGs, a proportion of which were ubiquitinated. The co-localization of TDP-43 with SGs could be fully prevented by inhibition of c-Jun N-terminal kinase (JNK). JNK inhibition did not prevent formation of HuR-positive SGs and did not prevent diffuse TDP-43 accumulation in the cytosol. In contrast, ERK or p38 inhibition prevented formation of both TDP-43 and HuR-positive SGs. JNK inhibition also inhibited TDP-43 SG localization in cells acutely treated with sodium arsenite and reduced the number of aggregates per cell in cultures transfected with C-terminal TDP-43 162-414 and 219-414 constructs. Conclusions Our studies are the first to demonstrate a critical role for kinase control of TDP-43 accumulation in SGs and may have important implications for development of treatments for FTD and ALS, targeting cell signal pathway control of TDP-43 aggregation.

TDP-43 proteinopathies (FTLD-U and ALS) are characterized by loss of nuclear TDP-43 expression and C-terminal TDP-43 fragmentation and accumulation in the cytoplasm. Recent studies have shown that TDP-43 can accumulate in RNA stress granules (SGs) in response to cell stresses. This could be associated with subsequent formation of aggregates. However, the pathway of endogenous TDP-43 accumulation in SGs during chronic disease is not understood. Aims: In this study we investigated the mechanism of TDP-43 processing and accumulation in SGs in neurons exposed to chronic oxidative stress. Neuronal cultures were treated with the mitochondrial inhibitor paraquat (24 hr) and examined for TDP-43 and SG processing. We found that mild toxicity induced by paraquat caused a loss of nuclear TDP-43, increased cytoplasmic accumulation of the 35 kDa C-terminal TDP-43 fragment and led to formation of TDP-43 and HuR-positive SGs, a proportion of which were ubiquitinated. The co-localization of TDP-43 with SGs could be completely blocked by inhibition of c-Jun N-terminal kinase (JNK). Inhibition of JNK did not prevent formation of HuR-positive SGs and did not prevent diffuse TDP-43 accumulation in the cytosol. In contrast, ERK inhibition prevented formation of both TDP-43 and HuR-positive SGs, Co-treatment of neurons with a copper-bis (thiosemicarbazone) complex (CuII(atsm)) inhibited JNK activity and TDP-43-positive SG formation, increased expression of key survival proteins and reduced oxidative stress and neurotoxicity. CuII(atsm) also inhibited abnormal TDP-43 processing, delayed disease onset and extended life in a G93A SOD1 murine model of ALS. Our studies are the first to demonstrate a critical role for JNK in TDP-43 accumulation in SGs and inhibition by a potentially therapeutic copper complex. These findings may have important implications for development of treatments for FTD and ALS, targeting cell signal pathway control of TDP-43 aggregation.

Ubiquitinated neuronal aggregates containing TDP-43 are pathological hallmarks in the spectrum of frontotemporal lobar dementia and amyotrophic lateral sclerosis. Changes to TDP-43 metabolism have also been reported in Alzheimer's disease brain tissue. In affected neurons, the TDP-43 undergoes C-terminal fragmentation, phosphorylation and ubiquitination and forms aggregates in the cytoplasm or nucleus. While in vitro studies have been able to re-capitulate these features using transfected cell culture models, little is known about the biochemical mechanisms that underlie pathological changes to endogenous TDP-43. As altered metal ion homeostasis and increased oxidative stress are central features of neurodegeneration, including FTD and ALS, we sought to determine the effects of these factors on endogenous TDP-43 metabolism in mammalian cells. Cultures of neuronal-like SY5Y cells were treated with biometals or subjected to oxidative insult and changes to endogenous TDP-43 metabolism examined by immunoblot and immunofluorescence. Treatment of SY5Y cells expressing endogenous TDP-43 with zinc (Zn) induced depletion of TDP-43 expression and formation of inclusions in the nucleus and cytoplasm that were TDP-43 positive. No evidence of C-terminal fragmentation, phosphorylation or ubiquitination was observed. The depletion and aggregation of TDP-43 was associated with the specific action of Zn and was not seen with copper or iron. Inclusions of TDP-43 were inhibited by treatment of cells with a cell permeable free radical scavenger (MnTMPyP) while exposure of cells to the superoxide generator, paraquat, induced similar formation of inclusions. These findings suggest that increased metal-associated oxidative stress, which is a common feature of neurodegeneration, may enhance aggregation of endogenous neuronal TDP-43. Our studies describe for the first time specific induction of endogenous TDP-43 aggregation in neuronal-like cells and suggest that specific Zn and oxidative stress-associated processes could affect TDP-43 metabolism in neurodegenerative diseases.