Neelima B. Chauhan

Neurotrophic factors in Alzheimer's and Parkinson's disease brain

The biomedical literature on the subject of neurotrophic growth factors has expanded prodigiously. This essay reviews neurotrophic factors (NTF) and their receptors in Alzheimers disease (AD) and Parkinsons disease (PD) brain and recent updates on receptor signaling. The hypotheses for specific NTF involvement in neurodegenerative diseases in human and as potential therapy are based mainly on experimental animal and in vitro models. There are wide gaps in information on regional synthesis and cell contents of NTFs and their receptors in human brain. Observations on AD brain indicate increases in NGF and decreases in BDNF in surviving neurons of hippocampus and certain neocortical regions and decreases in TrkA in cortex and nucleus basalis. In PD brain, the few data available indicate decreases in neuronal content of GDNF and bFGF in surviving substantia nigra dopaminergic neurons. There are very few data regarding age-dependent effects on NTFs and on their receptors in human brain. Since NTFs in neurons are subject to retrograde and, in at least some cases, to anterograde transport from and to target neurons, their effects may be related to synthesis in local or remote sites or to changes in axoplasmic transport. Also, certain NTFs and their receptors are found to be expressed in activated glia. Thus, comparative in situ data for transcription levels and protein contents for NTFs and their receptors in both sites of neuronal origin and termination in human brain are needed to understand their potential roles in treating human diseases.

Intracerebroventricular passive immunization with anti-Aβ antibody in Tg2576

Current Alzheimers disease (AD) research has established the fact that excessive genesis of Aβ derived from amyloidogenic processing of β‐amyloid (Aβ) precursor protein is fundamental to AD pathogenesis. There has been considerable interest in using immunization strategies for clearing excessive Aβ. Studies in animal models of AD have shown that active immunizations or systemic passive immunizations reduced cerebral plaque load and improved behavioral deficits. However, clinical translation of an active immunization strategy was interrupted because of evidence for meningoencephalitis produced in some patients who received Aβ vaccine. Studies in animal models have shown perimicrovascular hemorrhages and inflammation after sustained systemic immunizations in animals with vascular amyloid. In this light, our data showing the effects of a single intracerebroventricular (ICV) injection of anti‐Aβ in the Alzheimers Swedish mutant model Tg2576 are intriguing. We have previously demonstrated that a single ICV injection of anti‐Aβ into the third ventricle of 10‐month‐old Tg2576 mice reduced cerebral plaques, reversed Aβ‐induced depletion of presynaptic SNAP‐25, and abolished astroglial activation as seen 1 month post‐injection (Chauhan and Siegel [ 2002 ] J. Neurosci. Res. 69:10–23). The present report demonstrates that a single ICV injection of 10 μg anti‐Aβ in 10‐month‐old Tg2576 mice reduced cerebral plaques, with decreased inflammation at this stage as evidenced by a reduced number of interleukin‐1β‐positive microglia surrounding Congophilic plaques. Moreover, at this particular age, no microhemorrhage was discernible, as evidenced by the absence of hemosiderin deposition after a single ICV injection of anti‐Aβ. This is the first report demonstrating absence of microhemorrhage and reduced inflammation after the ICV introduction of anti‐Aβ in Tg2576 mice at 10 months of age. These facts indicate that, although invasive, ICV injection of anti‐Aβ may be a safer method of vaccination in AD, possibly through reducing the vascular exposure to antibody. Further studies are warranted to determine the lasting effects of a single ICV anti‐Aβ injection in animals with and without abundant plaque burden and at older ages.

Effects of Lovastatin and Pravastatin on Amyloid Processing and Inflammatory Response in TgCRND8 Brain

Previous studies suggest that treatment with statins reduce beta amyloid (Aβ) deposition in brains of mouse models of Alzheimers disease (AD) and may reduce the prevalence of AD in humans. Since lipophilicity influences the biological efficacy of statins, we compared the effects of lovastatin, a lipophilic statin, to effects of the hydrophilic pravastatin on amyloid processing and inflammatory responses in brain. Three-month old TgCRND8 mice expressing mutant human amyloid precursor protein (mHuAPP) were treated daily with various doses of either statin. After 1month, levels of cerebral soluble and fibrillar Aβ peptides, soluble sAPPα, and inflammatory cytokines were measured. Both statins caused dose-dependent reductions in total Aβ peptides with parallel increases in total sAPPα. At all doses, slightly greater effects were observed with lovastatin than with pravastatin. In contrast, only lovastatin significantly increased levels of IL-1β and of TNFα in a dose-dependent manner. Lovastatin, but not pravastatin, decreased succinic dehydrogenase and increased lactate dehydrogenase activities in skeletal muscle and increased TUNEL staining in liver. Our data demonstrate that both statins shift the balance of APP processing from excessive β-toward the normal α-cleavage while reducing the total amyloid burden in TgCRND8 brain and that lovastatin, but not pravastatin, potentiates cerebral inflammation and is associated with liver and muscle histotoxicity in these animals. These data show that pravastatin can reduce amyloid burden without potentiating inflammatory responses in brain and, therefore, may have a wider dose-range of safety than have lipophilic statins in the treatment or prevention of AD.

Oxidative insults to neurons and synapse are prevented by aged garlic extract and S-allyl- l -cysteine treatment in the neuronal culture and APP-Tg mouse model

J. Neurochem. (2011) 117, 388–402.

Chronic neurodegenerative consequences of traumatic brain injury

Traumatic brain injury (TBI) is a serious public health concern and a major cause of death and disability worldwide. Each year, an estimated 1.7 million Americans sustain TBI of which ~52,000 people die, ~275,000 people are hospitalized and 1,365,000 people are treated as emergency outpatients. Currently there are ~5.3 million Americans living with TBI. TBI is more of a disease process than of an event that is associated with immediate and long-term sensomotor, psychological and cognitive impairments. TBI is the best known established epigenetic risk factor for later development of neurodegenerative diseases and dementia. People sustaining TBI are ~4 times more likely to develop dementia at a later stage than people without TBI. Single brain injury is linked to later development of symptoms resembling Alzheimers disease while repetitive brain injuries are linked to later development of chronic traumatic encephalopathy (CTE) and/or Dementia Pugilistica (DP). Furthermore, genetic background of ß-amyloid precursor protein (APP), Apolipoprotein E (ApoE), presenilin (PS) and neprilysin (NEP) genes is associated with exacerbation of neurodegenerative process after TBI. This review encompasses acute effects and chronic neurodegenerative consequences after TBI.

Na,K-ATPase mRNA levels and plaque load in Alzheimer's disease

AbstractThe expression of Na,K-ATPase α1- and α3-mRNAs was analyzed byin situ hybridization in the superior frontal cortex and cerebellum of brains from five Alzheimers disease (AD), five nondemented age-matched, and three young control subjects. Brains with well-preserved RNA, tested by Northern hybridization of immobilized RNA with [32P]-labeled human β-actin riboprobe, were chosen for analysis.In situ hybridization was performed on formalin-fixed, 5 μm-thick Paraplast sections with [35S]-labeled riboprobes prepared by in vitro transcription of the respective linearized clones: a 537-bpEcoRI-PstI fragment of α1-cDNA and a 342-bpPstI-EcoRI fragment of α3-cDNA. In cortex, grains related to mRNA were measured by density per unit area in five cortical columns separated by 1.0–1.2 cm in each of two adjacent sections. Each cortical column of 180-μm width was divided into four depths orthogonal to the pial surface between the pia and the white matter. Amyloid plaques were counted in the same regions of adjacent sections. In addition, α3-mRNA grain clusters over individual pyramidal neurons within depth 4 were analyzed. We found the following significant changes (p<0.05):1.Increases in total α1-mRNA by 13–19% in AD compared to young and by 7–12% in AD compared to age-matched controls.2.Decrease in total α3-mRNA by 31–38% in AD compared to young and age-matched controls.3.Decrease in α3-mRNA content over individual pyramidal perikarya by 14% in normal aged brains without plaques compared to young controls, and by 44% in AD relative to young controls and by 35% compared to age-matched controls. No significant difference (p<0.2) was found with respect to α1- or α3-mRNA in cerebellar cortex or individual Purkinje cells among any of the groups. In addition, there was a trend toward an inverse correlation between the levels of α3-mRNA and of diffuse plaques, but not of neuritic plaques, in AD cases. In conclusion:1.The increases in α1-mRNA in AD may be related to an increased reactive gliosis.2.The declines in α3-mRNA per individual neuron found in normal aging occur prior to the formation of diffuse plaques and are greatly accelerated in AD.3.The declines in α3-mRNA per neuron found in normal aging may predispose to or potentiate AD pathogenesis.

Efficacy of anti-Aβ antibody isotypes used for intracerebroventricular immunization in TgCRND8

We have previously demonstrated that intracerebroventricular (ICV) injection of anti-Abeta (IgG1, kappa against the 1-28 region of Abeta) reduced cerebral amyloid plaques by 50% after 1 month without producing hemorrhage or activating IL-1beta responses in Tg2576 brain [N.B. Chauhan, G.J. Siegel, Reversal of amyloid beta toxicity in Alzheimers disease model Tg2576 by intraventricular antiamyloid beta antibody, J. Neurosci. Res. 69 (1) (2002) 10-23]. The current report compares the efficacy of IgG1, IgG2a and IgG2b isotypes of anti-Abeta against several different epitopes of Abeta in clearing cerebral Abeta after a single bolus ICV injection in TgCRND8. Consistent with earlier in vitro findings from other laboratories, these in vivo data demonstrate that all IgG1 isotype antibodies tested cleared cerebral Abeta more efficiently than did IgG2a and IgG2b antibodies without producing histotoxicity in brain, liver or kidney, while an antibody against the C-terminus of Abeta did not reduce plaques or diminish their accumulation with aging of the animals. Intriguingly, there was no significant difference between the Abeta-reducing efficiency of IgG1 anti-Abeta antibodies directed against residues 3-6, against residues 1-10 or against residues 1-28 of N-terminus Abeta.

Propentofylline attenuates tau hyperphosphorylation in Alzheimer's Swedish mutant model Tg2576.

Key pathological hallmarks of Alzheimers disease (AD) are the deposition of amyloid plaques containing Abeta-peptides and the formation of neurofibrillary tangles containing hyperphosphorylated tau. Propentofylline (PPF) is a synthetic xanthine derivative that inhibits phosphodiesterase and adenosine uptake. These effects of PPF influence many cellular functions including stimulating synthesis/release of nerve growth factor. We tested the effects of PPF on disease progression in transgenic mice overexpressing the Swedish mutant human APP (Tg2576). The untreated Tg mice show, together with increased amyloidogenesis, increased levels of tau hyperphosphorylation and increased ratios of the activated to inactivated GSK-3beta, one of the key kinases that can phosphorylate tau. One month of PPF feeding (40 mg/kg per day) reduced the burden of amyloid plaques and the levels of hyperphosphorylated tau and immunoreactive IL-1beta. In parallel with these changes, PPF reduced the activated form of GSK-3beta and increased the inactivated form of GSK-3beta, restoring their ratio almost to normal values. These results demonstrate that PPF can exert multiple protective effects on both amyloidogenesis and tau hyperphosphorylation in an animal model of AD. Our earlier report [Neurochem. Int. 43(3) (2003) 225] demonstrated that Tg2576 animals show decreased levels of mRNA for NGF with increased amyloid burden while feeding of PPF results in a major shift from beta-amyloidogenic to alpha-secretory processing of APP together with increased expression of NGF mRNA. The current new data enlarge our understanding of PPF effects in brain and of tau hyperphosphorylation in Tg animals and are consistent with the hypothesis that GSK-3beta is a nodal point linking amyloid and tau pathology. Therapeutic interventions directed toward multiple pathological processes may be more protective than treatments directed toward a single process. The new results reported here indicate that further testing of PPF as a potential therapy in AD is warranted.

Experimental Induction of Type 2 Diabetes in Aging-Accelerated Mice Triggered Alzheimer-Like Pathology and Memory Deficits

Alzheimers disease (AD) is an age-dependent neurodegenerative disease constituting ~95% of late-onset non-familial/sporadic AD, and only ~5% accounting for early-onset familial AD. Availability of a pertinent model representing sporadic AD is essential for testing candidate therapies. Emerging evidence indicates a causal link between diabetes and AD. People with diabetes are >1.5-fold more likely to develop AD. Senescence-accelerated mouse model (SAMP8) of accelerated aging displays many features occurring early in AD. Given the role played by diabetes in the pre-disposition of AD, and the utility of SAMP8 non-transgenic mouse model of accelerated aging, we examined if high fat diet-induced experimental type 2 diabetes in SAMP8 mice will trigger pathological aging of the brain. Results showed that compared to non-diabetic SAMP8 mice, diabetic SAMP8 mice exhibited increased cerebral amyloid-β, dysregulated tau-phosphorylating glycogen synthase kinase 3β, reduced synaptophysin immunoreactivity, and displayed memory deficits, indicating Alzheimer-like changes. High fat diet-induced type 2 diabetic SAMP8 mice may represent the metabolic model of AD.

Age-Dependent Organotypic Expression of Microtubule-Associated Proteins (MAP1, MAP2, and MAP5) in Rat Brain

Age-dependent changes in the distribution of microtubule-associated proteins (MAPs) were analyzed in young (3-months, N = 3) and old (24-months, N = 3) rat brain. In the young rats, MAP1 and MAP5 exhibited prominent immunostaining in the perikarya and dendrites whereas MAP2 was selectively localized in the dendrites. In the cerebellum, MAP2 was preferentially localized in finer and distal branches of Purkinje cell dendrites and in punctate deposits surrounding glomeruli. In general, aging resulted in obvious declines in MAP2- >> MAP1- and MAP5-immunoreactivities in the hippocampus and parietal cortex but no change in cerebellum. The results indicate that: (1) hippocampus is the most affected and cerebellum is the least affected region with regard to declines in MAPs-immunoreactivities in the aged rat brain; (2) dendrite-specific MAP2 is almost completely depleted from most dendrites in the hippocampus and cortex. In summary, loss of MAP2-immunoreactivity in the affected brain areas may be associated with age-related impairment of synaptic plasticity, cognition and memory functions.