A feature of most neurodegenerative diseases is the presence of "mis-folded proteins" that form aggregates, suggesting suboptimal activity of neuronal molecular chaperones. Heat shock protein 90 ...(Hsp90) is the master regulator of cell responses to "proteotoxic" stresses. Some Hsp90 modulators activate cascades leading to upregulation of additional chaperones. Novobiocin is a modulator at the C-terminal ATP-binding site of Hsp90. Of several novobiocin analogs synthesized and tested for protection against amyloid beta (Aβ)-induced neuronal death, "KU-32" was the most potent in protecting primary neurons, but did not increase expression of other chaperones believed to help clear misfolded proteins. However, KU-32 reversed Aβ-induced superoxide formation, activated Complex I of the electron transfer chain in mitochondria, and blocked the Aβ-induced inhibition of Complex I in neuroblastoma cells. A mechanism for these effects of KU-32 on mitochondrial metabolism appeared to be the inhibition of pyruvate dehydrogenase kinase (PDHK), both in isolated brain mitochondria and in SH-SY5Y cells. PDHK inhibition by the classic enzyme inhibitor, dichloroacetate, led to neuroprotection from Aβ
-induced cell injury similarly to KU-32. Inhibition of PDHK in neurons would lead to activation of the PDH complex, increased acetyl-CoA generation, stimulation of the tricarboxylic acid cycle and Complex I in the electron transfer chain, and enhanced oxidative phosphorylation. A focus of future studies may be on the potential value of PDHK as a target in AD therapy.
Intraneuronal calcium (Ca²⁺i) regulation is altered in aging brain, possibly because of the changes in critical Ca²⁺ transporters. We previously reported that the levels of the plasma membrane ...Ca²⁺-ATPase (PMCA) and the Vmax for enzyme activity are significantly reduced in synaptic membranes in aging rat brain. The goal of these studies was to use RNAi techniques to suppress expression of a major neuronal isoform, PMCA2, in neurons in culture to determine the potential functional consequences of a decrease in PMCA activity. Embryonic rat brain neurons and SH-SY5Y neuroblastoma cells were transfected with in vitro- transcribed short interfering RNA or a short hairpin RNA expressing vector, respectively, leading to 80% suppression of PMCA2 expression within 48 h. Fluorescence ratio imaging of free Ca²⁺i revealed that primary neurons with reduced PMCA2 expression had higher basal Ca²⁺i, slower recovery from KCl-induced Ca²⁺ transients, and incomplete return to pre-stimulation Ca²⁺ levels. Primary neurons and SH-SY5Y cells with PMCA2 suppression both exhibited significantly greater vulnerability to the toxicity of various stresses. Our results indicate that a loss of PMCA such as occurs in aging brain likely leads to subtle disruptions in normal Ca²⁺ signaling and enhanced susceptibility to stresses that can alter the regulation of Ca²⁺ homeostasis.
The cloning and characterization of the gene for the fourth subunit of a glutamate-binding protein complex in rat brain synaptic membranes are described. The cloned rat brain cDNA contained two open ...reading frames (ORFs) encoding 8.9- (PRO1) and 9.5-kDa (PRO2) proteins. The cDNA sequence matched contiguous genomic DNA sequences in rat chromosome 17. Both ORFs were expressed within the structure of a single brain mRNA and antibodies against unique sequences in PRO1- and PRO2-labeled brain neurons in situ, indicative of bicistronic gene expression. Dicistronic vectors in which ORF1 and ORF2 were substituted by either two different fluorescent proteins or two luciferases indicated concurrent, yet independent translation of the two ORFs. Transfection with noncapped mRNA led to cap-independent translation of only ORF2 through an internal ribosome entry sequence preceding ORF2. In vitro or cell expression of the cloned cDNA led to the formation of multimeric protein complexes containing both PRO1 and PRO2. These complexes had low affinity (+)-5-methyl-10,11-dihydro-5H-dibenzoa,dcyclohepten-5,10-imine (MK-801)-sensitive phencyclidine-binding sites. Overexpression of PRO1 and PRO2 in CHO cells, but not neuroblastoma cells, caused cell death within 24–48 h. The cytotoxicity was blocked by concurrent treatment with MK-801 or by two tetrahydroisoquinolines that bind to phencyclidine sites in neuronal membranes. Co-expression of two of the other subunits of the protein complex together with PRO1/PRO2 abrogated the cytotoxic effect without altering PRO1/PRO2 protein levels. Thus, this rare mammalian bicistronic gene coded for two tightly interacting brain proteins forming a low affinity phencyclidine-binding entity in a synaptic membrane complex.
The excitatory neurotransmitter glutamate has a role in neuronal migration and process elongation in the central nervous system (CNS). The effects of chronic glutamate hyperactivity on vesicular and ...protein transport within CNS neurons, that is, processes necessary for neurite growth, have not been examined previously. In this study, we measured the effects of lifelong hyperactivity of glutamate neurotransmission on axoplasmic transport in CNS neurons. We compared wild‐type (wt) to transgenic (Tg) mice over‐expressing the glutamate dehydrogenase gene Glud1 in CNS neurons and exhibiting increases in glutamate transmitter formation, release, and synaptic activation in brain throughout the lifespan. We found that Glud1 Tg as compared with wt mice exhibited increases in the rate of anterograde axoplasmic transport in neurons of the hippocampus measured in brain slices ex vivo, and in olfactory neurons measured in vivo. We also showed that the in vitro pharmacologic activation of glutamate synapses in wt mice led to moderate increases in axoplasmic transport, while exposure to selective inhibitors of ion channel forming glutamate receptors very significantly suppressed anterograde transport, suggesting a link between synaptic glutamate receptor activation and axoplasmic transport. Finally, axoplasmic transport in olfactory neurons of Tg mice in vivo was partially inhibited following 14‐day intake of ethanol, a known suppressor of axoplasmic transport and of glutamate neurotransmission. The same was true for transport in hippocampal neurons in slices from Glud1 Tg mice exposed to ethanol for 2 h ex vivo. In conclusion, endogenous activity at glutamate synapses regulates and glutamate synaptic hyperactivity increases intraneuronal transport rates in CNS neurons.
Lee et al. present an ex vivo and in vivo study of axonal transport in a transgenic mouse model of chronic glutamate neurotransmission hyperactivity, which over‐expresses the glutamate dehydrogenase gene (Glud1) in CNS neurons and exhibits increased glutamate transmitter formation, release, and synaptic activation. Glud1 versus wild‐type mice exhibited an increased rate of anterograde axoplasmic transport in hippocampal neurons in ex vivo and in olfactory neurons in vivo. Pharmacologic experiments in brain slices suggested a link between synaptic glutamate receptor activation and axoplasmic transport. Overall, the study demonstrates that endogenous Glu neurotransmission hyperactivity enhances anterograde axonal transport rates in the CNS neurons.
Mitochondrial DNA (mtDNA) may play a role in Alzheimer's disease (AD) and cognitive decline. A particular haplogroup of mtDNA, haplogroup J, has been observed more commonly in patients with AD than ...in cognitively normal controls.
We used two mtDNA haplogroups, H and J, to predict change in cognitive performance over five years. We hypothesized that haplogroup J carriers would show less cognitive resilience.
We analyzed data from 140 cognitively normal older adults who participated in the University of Kansas Alzheimer's Disease Research Center clinical cohort between 2011 and 2020. We used factor analysis to create three composite scores (verbal memory, attention, and executive function) from 11 individual cognitive tests. We performed latent growth curve modeling to describe trajectories of cognitive performance and change adjusting for age, sex, years of education, and APOE ɛ4 allele carrier status. We compared haplogroup H, the most common group, to haplogroup J, the potential risk group.
Haplogroup J carriers had significantly lower baseline performance and slower rates of improvement on tests of verbal memory compared to haplogroup H carriers. We did not observe differences in executive function or attention.
Our results reinforce the role of mtDNA in changes to cognitive function in a domain associated with risk for dementia, verbal memory, but not with other cognitive domains. Future research should investigate the distinct mechanisms by which mtDNA might affect performance on verbal memory as compared to other cognitive domains across haplogroups.
Altered neurotrophism in diabetic peripheral neuropathy (DPN) is associated in part with substantial degenerative changes
in Schwann cells (SCs) and an increased expression of the p75 neurotrophin ...receptor (p75 NTR ). Caveolin-1 (Cav-1) is highly expressed in adult SCs, and changes in its expression can regulate signaling through Erb
B2, a co-receptor that mediates the effects of neuregulins in promoting SC growth and differentiation. We examined the hypothesis
that hyperglycemia-induced changes in Cav-1 expression and p75 NTR signaling may contribute to altered neurotrophism in DPN by modulating SC responses to neuregulins. In an animal model of
type 1 diabetes, hyperglycemia induced a progressive decrease of Cav-1 in SCs of sciatic nerve that was reversed by insulin
therapy. Treatment of primary neonatal SCs with 20â30 m m d -glucose, but not l -glucose, was sufficient to inhibit transcription from the Cav-1 promoter and decrease Cav-1 mRNA and protein expression. Hyperglycemia prolonged the kinetics of Erb B2 phosphorylation
and significantly enhanced the mitogenic response of SCs to neuregulin1-β1, and this effect was mimicked by the forced down-regulation
of Cav-1. Intriguingly, nerve growth factor antagonized the enhanced mitogenic response of SCs to neuregulin1-β1 and inhibited
the glucose-induced down-regulation of Cav-1 transcription, mRNA, and protein expression through p75 NTR -dependent activation of JNK. Our data suggest that Cav-1 down-regulation may contribute to altered neurotrophism in DPN
by enhancing the response of SCs to neuregulins and that p75 NTR -mediated JNK activation may provide a mechanism for the neurotrophic modulation of hyperglycemic stress.
Abstract
Background
Mitochondrial genetics are important in the etiology of Alzheimer’s disease (AD). Based on the polymorphisms in mitochondrial DNA (mtDNA) the population can be classified into ...subgroups called the haplogroups. Previous studies have explored the association of haplogroups and genetic variants in APOE ε4 with AD but the results are inconsistent. Also, patients with mild cognitive impairment (MCI) at baseline often progress differently over several years of follow up.
Method
We carried out a cross‐sectional study to examine the association of the rate of incidence of AD with APOE ε4 genotype and haplogroups. The data collected at the University of Kansas AD Center (KU ADC) consisting of 146 AD and 265 normal subjects, and the data collected by AD Neuroimaging Initiative (ADNI) consisting of 244 AD and 242 normal subjects were used for these analyses. Logistic regression and Fisher Exact tests were used to explore the associations. We also carried out the association analyses of the differences in the disease progression rates from MCI to AD among the haplogroups using both datasets.
Result
Rates of incidence of AD were statistically significantly different among the haplogroups (2.2 × 10
−8
), with differing strengths of association across haplogroups. APOE ε4 was significantly associated with AD overall (p‐value = 1.9 × 10
−11
) and the association further varied by haplogroups. The results of the KU ADC population were consistent with those of the ADNI data. Out of 112 MCI subjects at baseline in KU ADC, 26 progressed to AD and 20 reverted back to normal at the last clinical visit. In ADNI, 172 progressed to AD and 42 reverted back out of 482 MCI at baseline. For both datasets, the proportion of subjects who progressed to AD differed by haplogroups. APOE ε4 genotype was significantly associated with increased risk of progression from MCI to AD (p‐value = 8.6 × 10
−7
KUADC and p‐value = 1.33 × 10
−9
ADNI).
Conclusion
The rate of incidence of AD differed by mtDNA haplogroup and the strength of association further differed by APOE ε4 genotype. The rates of progression of MCI subjects to AD also differed by haplogroups and APOE ε4 genotype.
Background
Mitochondrial genetics are important in the etiology of Alzheimer’s disease (AD). Based on the polymorphisms in mitochondrial DNA (mtDNA) the population can be classified into subgroups ...called the haplogroups. Previous studies have explored the association of haplogroups and genetic variants in APOE ε4 with AD but the results are inconsistent. Also, patients with mild cognitive impairment (MCI) at baseline often progress differently over several years of follow up.
Method
We carried out a cross‐sectional study to examine the association of the rate of incidence of AD with APOE ε4 genotype and haplogroups. The data collected at the University of Kansas AD Center (KU ADC) consisting of 146 AD and 265 normal subjects, and the data collected by AD Neuroimaging Initiative (ADNI) consisting of 244 AD and 242 normal subjects were used for these analyses. Logistic regression and Fisher Exact tests were used to explore the associations. We also carried out the association analyses of the differences in the disease progression rates from MCI to AD among the haplogroups using both datasets.
Result
Rates of incidence of AD were statistically significantly different among the haplogroups (2.2 × 10−8), with differing strengths of association across haplogroups. APOE ε4 was significantly associated with AD overall (p‐value = 1.9 × 10−11) and the association further varied by haplogroups. The results of the KU ADC population were consistent with those of the ADNI data. Out of 112 MCI subjects at baseline in KU ADC, 26 progressed to AD and 20 reverted back to normal at the last clinical visit. In ADNI, 172 progressed to AD and 42 reverted back out of 482 MCI at baseline. For both datasets, the proportion of subjects who progressed to AD differed by haplogroups. APOE ε4 genotype was significantly associated with increased risk of progression from MCI to AD (p‐value = 8.6 × 10−7 KUADC and p‐value = 1.33 × 10−9 ADNI).
Conclusion
The rate of incidence of AD differed by mtDNA haplogroup and the strength of association further differed by APOE ε4 genotype. The rates of progression of MCI subjects to AD also differed by haplogroups and APOE ε4 genotype.
Some epidemiologic studies associate traumatic brain injury (TBI) with Alzheimer's disease (AD).
To test whether a TBI-induced acceleration of age-related mitochondrial change could potentially ...mediate the reported TBI-AD association.
We administered unilateral controlled cortical impact (CCI) or sham injuries to 5-month-old C57BL/6J and tau transgenic rTg4510 mice. In the non-transgenics, we assessed behavior (1-5 days, 1 month, and 15 months), lesion size (1 and 15 months), respiratory chain enzymes (1 and 15 months), and mitochondrial DNA copy number (mtDNAcn) (1 and 15 months) after CCI/sham. In the transgenics we quantified post-injury mtDNAcn and tangle burden.
In the non-transgenics CCI caused acute behavioral deficits that improved or resolved by 1-month post-injury. Protein-normalized complex I and cytochrome oxidase activities were not significantly altered at 1 or 15 months, although complex I activity in the CCI ipsilesional cortex declined during that period. Hippocampal mtDNAcn was not altered by injury at 1 month, increased with age, and rose to the greatest extent in the CCI contralesional hippocampus. In the injured then aged transgenics, the ipsilesional hippocampus contained less mtDNA and fewer tangles than the contralesional hippocampus; mtDNAcn and tangle counts did not correlate.
As mice age their brains increase mtDNAcn as part of a compensatory response that preserves mitochondrial function, and TBI enhances this response. TBI may, therefore, increase the amount of compensation required to preserve late-life mitochondrial function. If TBI does modify AD risk, altering the trajectory or biology of aging-related mitochondrial changes could mediate the effect.
Introduction
Inherited mitochondrial DNA (mtDNA) variants may influence Alzheimer's disease (AD) risk.
Methods
We sequenced mtDNA from 146 AD and 265 cognitively normal (CN) subjects from the ...University of Kansas AD Center (KUADC) and assigned haplogroups. We further considered 244 AD and 242 CN AD Neuroimaging Initiative (ADNI) subjects with equivalent data.
Results
Without applying multiple comparisons corrections, KUADC haplogroup J AD and CN frequencies were 16.4% versus 7.6% (P = .007), and haplogroup K AD and CN frequencies were 4.8% versus 10.2% (P = .063). ADNI haplogroup J AD and CN frequencies were 10.7% versus 7.0% (P = .20), and haplogroup K frequencies were 4.9% versus 8.7% (P = .11). For the combined 390 AD and 507 CN cases haplogroup J frequencies were 12.8% versus 7.3% (P = .006), odds ratio (OR) = 1.87, and haplogroup K frequencies were 4.9% versus 9.5% (P = .010), OR = 0.49. Associations remained significant after adjusting for apolipoprotein E, age, and sex.
Conclusion
This exploratory analysis suggests inherited mtDNA variants influence AD risk.
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