Transcriptional and translational regulatory mechanisms during normal aging of the mammalian brain and in Alzheimer's disease

Chinese nutraceuticals and physical activity; their role in neurodegenerative tauopathies

The onset of neurodegenerative disease has not only been a major cause of scientific worry, but of economic burden to the health system. This condition has been further attributed to mis-stability, deletion or mutation of tau protein, causing the onset of Corticobasal degeneration, Pick's diseases, Progressive supranuclear palsy, Argyrophilic grains disease, Alzheimer's diseases etc. as scientifically renowned. This is mainly related to dysregulation of translational machinery, upregulation of proinflammatory cytokines and inhibition of several essential cascades such as ERK signaling cascade, GSK3β, CREB, and PKA/PKB (Akt) signaling cascades that enhances protein processing, normal protein folding, cognitive function, and microtubule associated tau stability. Administration of some nutrients and/or bioactive compounds has a high tendency to impede tau mediated inflammation at neuronal level. Furthermore, prevention and neutralization of protein misfolding through modulation of microtubule tau stability and prevention of protein misfolding is by virtue few of the numerous beneficial effects of physical activity. Of utmost important in this study is the exploration of promising bioactivities of nutraceuticals found in china and the ameliorating potential of physical activity on tauopathies, while highlighting animal and in vitro studies that have been investigated for comprehensive understanding of its potential and an insight into the effects on human highly probable to tau mediated neurodegeneration.

Tau-mediated dysregulation of RNA: Evidence for a common molecular mechanism of toxicity in frontotemporal dementia and other tauopathies

Frontotemporal dementias (FTDs) encompass several disorders commonly characterized by progressive frontotemporal lobar degeneration and dementia. Pathologically, TDP-43, FUS, dipeptide repeats, and tau constitute the protein aggregates in FTD, which in turn coincide with heterogeneity in clinical variants. The underlying molecular etiology explaining the formation of each type of protein aggregate remains unclear; however, dysregulated RNA metabolism rises as a common pathogenic factor. Alongside with TDP-43 and FUS, which bind to and regulate RNA dynamics, emerging data suggest that tau may also regulate RNA metabolism and translation. The complex mechanisms that drive translational selectivity in turn regulate the broad clinical presentation of FTDs. Here, we focus on the enigmatic relationship between tau and RNA and review the mechanisms of tau-mediated dysregulation of RNA in tauopathies such as FTD.

Hyperphosphorylation of RNA polymerase II and reduced neuronal RNA levels precede neurofibrillary tangles in Alzheimer disease

Affected neurons of Alzheimer disease (AD) brain are distinguished by the presence of the cell cycle cdc2 kinase and mitotic phosphoepitopes. A significant body of previous data has documented a decrease in neuronal RNA levels and nucleolar volume in AD brain. Here we present evidence that integrates these seemingly distinct findings and offers an explanation for the degenerative outcome of the disease. During mitosis cdc2 phosphorylates and inhibits the major transcriptional regulator RNA polymerase II (RNAP II). We therefore investigated cdc2 phosphorylation of RNAP II in AD brain. Using the H5 and H14 monoclonal antibodies specific for the cdc2-phosphorylated sites in RNAP II, we found that the polymerase is highly phosphorylated in AD. Moreover, RNAP II in AD translocates from its normally nuclear compartment to the cytoplasm of affected neurons, where it colocalizes with cdc2. These M phase-like changes in RNAP II correlate with decreased levels of poly-A RNA in affected neurons. Significantly, they precede tau phosphorylation and neurofibrillary tangle formation. Our data support the hypothesis that inappropriate activation of the cell cycle cdc2 kinase in differentiated neurons contributes to neuronal dysfunction and degeneration in part by inhibiting RNAP II and cellular processes dependent on transcription.

Two distinct secretory ribonucleases from human cerebrum: purification, characterization and relationships to other ribonucleases

Two RNAases from human cerebrum were purified to an electrophoretically homogeneous state and their molecular masses were 22.0 kDa (tentatively called RNAase HB-1) and 19.0 kDa (RNAase HB-2). Analyses of the amino acid compositions, N-terminal amino acid sequences and catalytic properties of these enzymes provided strong evidence that they were strictly related to the secretory (sec) RNAases, such as the pancreatic enzyme, very similar immunologically to urinary sec RNAase, but clearly distinguishable from urinary non-secretory (nonsec) RNAase. There were several differences between HB-1 and HB-2, namely their immunological reactivities with specific antibodies, heat-stabilities, attached carbohydrate moieties and molecular masses. In particular, HB-2 appeared to be nonglycosylated, in view of its lack of affinity for several conjugated lectins, the absence of hexosamine and no change in electrophoretic mobility before and after peptide:N-glycosidase F digestion, whereas HB-1 and human sec RNAases purified from kidney, pancreas and urine all appeared to be glycosylated, as they moved to the same position as HB-2 when electrophoresed after glycosidase digestion. An antibody against urinary sec RNAase inhibited 75% and 20% of the total activity of the crude cerebral extract against RNA at pH 8.0 and 6.0 respectively, whereas an antibody against urinary nonsec RNAase had no such inhibitory effect. These findings suggest that yet another type(s) of cerebral RNAase, which is unable to cross-react immunologically with sec and nonsec RNAases, may exist. Two RNAases corresponding to HB-1 and HB-2 were identified in fresh cerebrospinal fluid.

Heat shock protein (hsx70) mRNA expression in human brain: effects of neurodegenerative disease and agonal state

Heat shock proteins (hsps) are involved in the response by cells to stress including hyperthermia, hypoxia and injury. Previous work has demonstrated expression of messenger RNA (mRNA) encoding 70 kDa hsps (hsp70) in animal brain in response to stimuli such as these. We have used in situ hybridization histochemistry to assess the distribution and quantity of a specific hsp70 (called hsx70) mRNA in frontal cortex and cerebellum from normal and demented patients whose pre-mortem course had been documented. In cortex, hsx70 mRNA was concentrated over pia mater and glia but was also present over neurons; in cerebellum, hsx70 mRNA was prominent over granule cells but absent from Purkinje cells. Detection of hsx70 mRNA did not correlate with pre-mortem factors such as pyrexia or coma. Increased hsx70 mRNA was found in frontal cortex white matter in Alzheimer's disease and in a mixed group of other neurodegenerative disorders. No changes occurred in cerebellum. The data provide further evidence for altered hsp gene expression in dementia, and support the existence of a stress response occurring in brains affected by such diseases.

Molecular and cellular biology of Alzheimer amyloid

Alzheimer's Disease (AD), a disorder of unknown etiology, is the most common form of adult-onset dementia and is characterized by severe intellectual deterioration. The definitive diagnosis of AD is made by postmortem examination of the brain, which reveals large quantities of neurofibrillary tangles (NFT) and senile plaques within the parenchyma. The NFT are composed of paired helical filaments associated with several cytoskeletal proteins. The primary protein component of senile plaques is beta/A4 amyloid, a 42-43 amino acid peptide derived from a much larger molecule, the amyloid precursor protein (APP). Vascular beta/A4 amyloidosis is also prevalent in the disease. The mechanism by which beta/A4 amyloid accumulates in the AD brain is unknown. Recent research has demonstrated that the precursor molecule, APP, is a transmembrane protein with a large extracytoplasmic domain, a membrane spanning region that includes the portion that gives rise to beta/A4 amyloid, and a short intracytoplasmic domain. The precursor has multiple forms among which are those that differ by a variable length insert within the extracytoplasmic domain. The insert has sequence homology to the family of Kunitz protease inhibitor proteins. Cellular and animal models have been developed to study the nature of APP processing and the biological and behavioral consequences of beta/A4 amyloidosis. The results of such studies indicate that the normal processing of APP involves enzymatic cleavage of the molecule within the beta/A4 amyloid region, thus preventing the accumulation of beta/A4 in the normal brain. The factors leading to abnormal processing of APP, and consequent beta/A4 amyloid accumulation within the AD brain, have yet to be identified. In cell culture, the biological effects associated with beta/A4 amyloid include neurotrophic and neurotoxic activities, while the peptide has also been shown to have dramatic behavioral effects in animal models.

Regional and neuronal reductions of polyadenylated messenger RNA in Alzheimer's disease

Messenger RNA (mRNA) is the key intermediate in the gene expression pathway. The amount of mRNA in Alzheimer's disease (AD) brains has been determined using in situ hybridization histochemistry (ISHH) to detect the poly(A) tails of polyadenylated mRNA (poly(A) + mRNA). On a regional basis, AD cases had significantly less poly(A) + mRNA than controls in hippocampus (field CA3) and cerebellum (granule cell layer). Analysis of constituent pyramidal neurons showed mean reductions per cell within AD hippocampus (field CA3) and temporal cortex, but not in visual cortex. Similar changes were seen in a small group of non-AD dementias. The finding of reduced poly(A) + mRNA content is another indication of the altered brain gene expression occurring in AD. It is proposed that measurement of poly(A) + mRNA may be valuable in identifying functionally impaired neuronal populations. The methodology also provides a means by which changes in the quantitative distribution of individual mRNAs can be determined relative to that of poly(A) + mRNA as a whole.

Increased muscarinic receptor messenger RNA in Alzheimer's disease temporal cortex demonstrated by in situ hybridization histochemistry

A 35S-labelled synthetic oligonucleotide directed against part of the mRNA coding for the M1 subtype muscarinic receptor was used for in situ hybridization histochemistry in sections of human temporal cortex. M1 receptor mRNA was found in cell populations throughout the grey matter, especially in pyramidal cells. Quantitative densitometric analysis of autoradiograms was used to compare levels of this mRNA between Alzheimer's disease and controls. A significant (2.7-fold) increase in hybridization signal was found in Alzheimer's disease cases, both in absolute terms and relative to total polyadenylated mRNA as determined by hybridization with an oligodeoxythymidine probe. Elevated levels of muscarinic receptor mRNA may reflect up-regulation of transcription of this gene in response to the cholinergic deficits occurring in the disease.

Role of ribonuclease and ribonuclease inhibitor activities in Alzheimer's disease

It has been suggested that defects in the relationship between ribonuclease and its proteinaceous inhibitor could be a contributory factor in Alzheimer's disease. We have investigated this possibility further by analysing free and bound enzyme activities and the activity of the inhibitor in nine regions of diseased and normal brain. These were chosen to include areas known to be affected by the disease, regions not histologically affected but thought to be involved in the disease process, and areas not thought to be involved in the disease. Neither the enzyme nor its inhibitor is defective in its activities in the chosen areas of Alzheimer's disease brain when compared with those of carefully age-matched controls.

Molecular biology in psychiatric research: Alzheimer's disease as a paradigm

As illustration of the integration of molecular biological studies into psychiatric research, use of molecular techniques in the study of Alzheimer's disease is described, and the resultant observation of otherwise undetectable pathological changes is noted. Using postmortem Alzheimer brain messenger RNA, recombinant DNA studies led to the ability to clone and characterize the expressed genetic transcript for amyloid. Application of this methodology is discussed in terms of establishing cellular and animal models for a neuropsychiatric disease.

Molecular and genetic investigations on Alzheimer brain amyloid

Amyloid-containing plaques are a characteristic feature of the Alzheimer's disease brain and have been the object of study for decades. Only recently, however, have molecular and genetic techniques been applied to examination of amyloid in order to understand the factors that contribute to the accumulation of plaques in dementia. Current investigations have focused on the structure and properties of the amyloid protein, its corresponding messenger RNA, its cellular site of production, and its chromosomal site of origin. These data are discussed in the present review.

Preparation of a recombinant cDNA library from poly(A+) RNA of the Alzheimer brain. Identification and characterization of a cDNA copy encoding a glial-specific protein

Studies were undertaken to assess the extent to which messenger RNA prepared from the postmortem Alzheimer's disease (AD) brain can be used for the successful preparation of a recombinant cDNA library. Initial experiments focused on the glial-specific marker glial fibrillary acidic protein (GFAP) since GFAP expression appeared to be a model for further studies on mRNAs that may continue to be expressed at high levels in the vicinity of lesioned sites in the AD brain. An AD cDNA library, prepared in the lambda gt11 expression vector system contained GFAP-specific recombinants. One of these was sequenced and the insert was shown to exhibit 88% homology with the similar sequence from mouse GFAP. As established by Northern blots, the size of the GFAP mRNA prepared from the routinely acquired postmortem AD cortex, approximately 2.7 kb, was the same as from a neurologically normal control brain. These results agree with earlier studies on GFAP mRNA from fresh mouse brain. The results demonstrate that in the postmortem AD brain, astroglial-specific mRNA remains sufficiently stable for molecular genetic analysis and may serve as a useful model for examining the genetic expression of mRNAs that may be related to the molecular pathogenesis and the etiology of AD.

The postmortem Alzheimer brain is a source of structurally and functionally intact astrocytic messenger RNA

Although the precise role of astrocytes in the pathogenesis of Alzheimer's disease (AD) is currently undefined, studies carried out at the molecular level may lead to new insights into the functioning of this class of brain cells in dementia. In order to facilitate such investigations, methods are described that establish that structurally and functionally intact messenger RNA (mRNA) for an astrocytic marker, glial fibrillary acidic protein (GFAP), is present in the postmortem Alzheimer's disease brain after long postmortem intervals. Rapid preparative procedures were used to obtain poly(A)+ RNA from postmortem control and AD cortices. In vitro protein synthesis was carried out in a reticulocyte system. Relative to controls, AD mRNA synthesized a two-fold higher level of a 50,000 mol.wt. protein that was immunologically identified as GFAP. High levels of GFAP synthesis by purified mRNA from AD cortices was independent of age at death and postmortem interval up to 24 h. Northern blot hybridization using a cloned human GFAP riboprobe was used to evaluate postmortem GFAP mRNA stability. No appreciable degradation products of GFAP mRNA were observed on Northern blots for at least 10 h postmortem in poly(A)+ RNA extracted from the AD brain. The described methodology demonstrates that the postmortem AD brain is an excellent source of functionally and structurally intact astrocyte-specific mRNA.

Molecular cloning of amyloid cDNA derived from mRNA of the Alzheimer disease brain: coding and noncoding regions of the fetal precursor mRNA are expressed in the cortex

To gain insight into factors associated with the excessive accumulation of beta-amyloid in the Alzheimer disease (AD) brain, the present studies were initiated to distinguish between a unique primary structure of the AD-specific amyloid precursor mRNA vis a vis other determinants that may affect amyloid levels. Previous molecular cloning experiments focused on amyloid derived from sources other than AD cases. In the present work, we cloned and characterized amyloid cDNA derived directly from AD brain mRNA. Poly(A)+ RNA from AD cortices was used for the preparation of lambda gt11 recombinant cDNA libraries. An insert of 1564 nucleotides was isolated that included the beta-amyloid domain and corresponded to 75% of the coding region and approximately equal to 70% of the 3'-noncoding region of the fetal precursor amyloid cDNA reported by others. On RNA blots, the AD amyloid mRNA consisted of a doublet of 3.2 and 3.4 kilobases. In control and AD cases, the amyloid mRNA levels were nonuniform and were independent of glial-specific mRNA levels. Based on the sequence analysis data, we conclude that a segment of the amyloid gene is expressed in the AD cortex as a high molecular weight precursor mRNA with major coding and 3'-noncoding regions that are identical to the fetal brain gene product.