The circadian dynamics of the hippocampal transcriptome and proteome is altered in experimental temporal lobe epilepsy

Gene and protein expressions display circadian oscillations, which can be disrupted in diseases in most body organs. Whether these oscillations occur in the healthy hippocampus and whether they are altered in epilepsy are not known. We identified more than 1200 daily oscillating transcripts in the hippocampus of control mice and 1600 in experimental epilepsy, with only one-fourth oscillating in both conditions. Comparison of gene oscillations in control and epilepsy predicted time-dependent alterations in energy metabolism, which were verified experimentally. Although aerobic glycolysis remained constant from morning to afternoon in controls, it increased in epilepsy. In contrast, oxidative phosphorylation increased in control and decreased in epilepsy. Thus, the control hippocampus shows circadian molecular remapping, which is altered in epilepsy. We suggest that the hippocampus operates in a different functioning mode in epilepsy. These alterations need to be considered when studying epilepsy mechanisms, designing drug treatments, and timing their delivery.

Biochemical Staging of Synucleinopathy and Amyloid Deposition in Dementia With Lewy Bodies

The primary feature of dementia with Lewy bodies (DLB) is the aggregation of alpha-synuclein into characteristic lesions: Lewy bodies (LBs) and Lewy neurites. However, in most of DLB cases, LBs are associated with neurofibrillary tangles and amyloid plaques (both Alzheimer disease [AD]-related lesions). We wanted to determine if this overlap of lesions is statistical, as a result of the late onset of both diseases, or results from a specific physiopathological synergy between synucleinopathy and either tauopathy or amyloid pathology. All patients with DLB from our prospective and multidisciplinary study were analyzed. These cases were compared with cases with pure AD and patients with Parkinson disease and controls. All cases were analyzed thoroughly at the neuropathologic and biochemical levels with a biochemical staging of aggregated alpha-synuclein, tau, and Abeta species. All sporadic cases of DLB were associated with abundant deposits of Abeta x-42 that were similar in quality and quantity to those of AD. Amyloid precursor protein (APP) dysfunction is a risk factor for AD as demonstrated by pathogenic mutations and Abeta accumulation. The constant and abundant Abeta x-42 deposition in sporadic DLB suggests that synucleinopathy is also promoted by APP dysfunction. Therefore, we conclude that APP is a therapeutic target for both AD and DLB.

Association of ATP synthase alpha-chain with neurofibrillary degeneration in Alzheimer's disease

Amyloid deposits and neurofibrillary tangles (NFT) are the two hallmarks that characterize Alzheimer's disease (AD). In order to find the molecular partners of these degenerating processes, we have developed antibodies against insoluble AD brain lesions. One clone, named AD46, detects only NFT. Biochemical and histochemistry analyses demonstrate that the labeled protein accumulating in the cytosol of Alzheimer degenerating neurons is the alpha-chain of the ATP synthase. The cytosolic accumulation of the alpha-chain of ATP synthase is observed even at early stages of neurofibrillary degenerating process. It is specifically observed in degenerating neurons, either alone or tightly associated with aggregates of tau proteins, suggesting that it is a new molecular event related to neurodegeneration. Overall, our results strongly suggest the implication of the alpha-chain of ATP synthase in neurofibrillary degeneration of AD that is illustrated by the cytosolic accumulation of this mitochondrial protein, which belongs to the mitochondrial respiratory system. This regulatory subunit of the respiratory complex V of mitochondria is thus a potential target for therapeutic and diagnostic strategies.

Mice transgenic for the human myotonic dystrophy region with expanded CTG repeats display muscular and brain abnormalities

The autosomal dominant mutation causing myotonic dystrophy (DM1) is a CTG repeat expansion in the 3'-UTR of the DM protein kinase (DMPK) gene. This multisystemic disorder includes myotonia, progressive weakness and wasting of skeletal muscle and extramuscular symptoms such as cataracts, testicular atrophy, endocrine and cognitive dysfunction. The mechanisms underlying its pathogenesis are complex. Recent reports have revealed that DMPK gene haploinsufficiency may account for cardiac conduction defects whereas cataracts may be due to haploinsufficiency of the neighboring gene, the DM-associated homeobox protein (DMAHP or SIX5) gene. Furthermore, mice expressing the CUG expansion in an unrelated mRNA develop myotonia and myopathy, consistent with an RNA gain of function. We demonstrated that transgenic mice carrying the CTG expansion in its human DM1 context (>45 kb) and producing abnormal DMPK mRNA with at least 300 CUG repeats, displayed clinical, histological, molecular and electrophysiological abnormalities in skeletal muscle consistent with those observed in DM1 patients. Like DM1 patients, these transgenic mice show abnormal tau expression in the brain. These results provide further evidence for the RNA trans-dominant effect of the CUG expansion, not only in muscle, but also in brain.

Dysregulation of human brain microtubule-associated tau mRNA maturation in myotonic dystrophy type 1

Intraneuronal aggregates of hyperphosphorylated tau proteins, referred to as pathological tau, are found in brain areas of demented patients affected by numerous different neurodegenerative disorders. We previously described a particular biochemical profile of pathological tau proteins in myotonic dystrophy type 1 (DM1). This multisystemic disorder is characterized by an unstable CTG repeat expansion in the 3'-untranslated region of the DM protein kinase gene. In the human central nervous system, tau proteins consist of six isoforms that differ by the presence or absence of the alternatively spliced exons 2, 3 and 10. Here we show that the pattern of tau isoforms aggregated in DM1 brain lesions is characteristic. It consists mainly of the aggregation of the shortest human tau isoform. A disruption in normal tau isoform expression consisting of a reduced expression of tau isoforms containing the exon 2 was observed at both the mRNA and protein levels. Large expanded CTG repeats were detected and showed marked somatic heterogeneity between DM1 cases and in cortical brains regions analysed. Our data suggest a relationship between the CTG repeat expansion and the alteration of tau expression showing that DM1 is a peculiar tauopathy.