Carl W. Cotman

Fibril specific, conformation dependent antibodies recognize a generic epitope common to amyloid fibrils and fibrillar oligomers that is absent in prefibrillar oligomers

BackgroundAmyloid-related degenerative diseases are associated with the accumulation of misfolded proteins as amyloid fibrils in tissue. In Alzheimer disease (AD), amyloid accumulates in several distinct types of insoluble plaque deposits, intracellular Aβ and as soluble oligomers and the relationships between these deposits and their pathological significance remains unclear. Conformation dependent antibodies have been reported that specifically recognize distinct assembly states of amyloids, including prefibrillar oligomers and fibrils.ResultsWe immunized rabbits with a morphologically homogeneous population of Aβ42 fibrils. The resulting immune serum (OC) specifically recognizes fibrils, but not random coil monomer or prefibrillar oligomers, indicating fibrils display a distinct conformation dependent epitope that is absent in prefibrillar oligomers. The fibril epitope is also displayed by fibrils of other types of amyloids, indicating that the epitope is a generic feature of the polypeptide backbone. The fibril specific antibody also recognizes 100,000 × G soluble fibrillar oligomers ranging in size from dimer to greater than 250 kDa on western blots. The fibrillar oligomers recognized by OC are immunologically distinct from prefibrillar oligomers recognized by A11, even though their sizes overlap broadly, indicating that size is not a reliable indicator of oligomer conformation. The immune response to prefibrillar oligomers and fibrils is not sequence specific and antisera of the same specificity are produced in response to immunization with islet amyloid polypeptide prefibrillar oligomer mimics and fibrils. The fibril specific antibodies stain all types of amyloid deposits in human AD brain. Diffuse amyloid deposits stain intensely with anti-fibril antibody although they are thioflavin S negative, suggesting that they are indeed fibrillar in conformation. OC also stains islet amyloid deposits in transgenic mouse models of type II diabetes, demonstrating its generic specificity for amyloid fibrils.ConclusionSince the fibril specific antibodies are conformation dependent, sequence-independent, and recognize epitopes that are distinct from those present in prefibrillar oligomers, they may have broad utility for detecting and characterizing the accumulation of amyloid fibrils and fibrillar type oligomers in degenerative diseases.

Bax Protein Expression Is Increased in Alzheimer's Brain: Correlations with DNA Damage, Bcl-2 Expression, and Brain Pathology

We have shown that many neurons in Alzheimers disease (AD) exhibit terminal deoxynucleotidyl transferase (TdT) labeling for DNA strand breaks, and upregulation of Bcl-2 is associated with neurons exhibiting nuclear DNA fragmentation, while downregulation of Bcl-2 is associated with tangle-bearing neurons in AD brains. Consequently, we examined the expression of bcl-associated X (Bax) protein in AD brain. Immunoreactivity for Bax was seen in neurons and microglia of the hippocampal formation, and was elevated in the majority of AD cases as compared to control cases. Interestingly, 3 transitional cases, which had mild degeneration changes, exhibited relatively high levels of Bax immunoreactivity. Most Bax-positive neurons showed either TdT-labeled nuclei or Bcl-2 immunoreactivity. Although Bax immunoreactivity was detected within most early tangle-bearing neurons, many Bax-positive neurons did not colocalize with later-stage tangle-bearing neurons. In regions containing relatively few tangles in mild AD brains, many TdT-labeled neurons were immunolabeled with Bax antibody and most of them lacked evidence of neurofibrillary changes. These findings suggest that Bax may contribute to neuronal cell death in AD. Furthermore, DNA damage and the upregulation of Bax appear to precede tangle formation or may represent an alternative pathway of cell death in AD.

Re-establishment of electrophysiologically functional entorhinal cortical input to the dentate gyrus deafferented by ipsilateral entorhinal lesions: Innervation by the contralaeral entorhinal cortex

SummaryWe have unilaterally ablated the entorhinal cortex of the developing rat, thereby removing the major synaptic input to the ipsilateral dentate gyrus. We have then examined the efferent projections of the remaining contralateral entorhinal cortex to determine if these might reoccupy the synaptic territory vacated by the ipsilateral entorhinal fibers. By placing lesions in the remaining contralateral entorhinal cortex, and tracing the resulting degeneration products, we show that the contralateral entorhinal projection is reorganized, establishing an anomalous terminal projection to the dentate gyrus deafferented by the initial lesion. The result is a contralateral entorhinal innervation of the dentate gyrus which normally receives only ipsilateral entorhinal afferents.In addition, we investigate the functional capacity of these anomalous contralateral projections. We show that stimulation of the entorhinal cortex in the normal animal never results in short latency activation of the granule cells contralateral to the stimulating electrode, whereas in the lesioned animals, the contralateral entorhinal stimulation results in a short latency, apparently monosynaptic, evoked potential in the dentate gyrus which had been deprived of its ipsilateral entorhinal innervation. Furthermore, this stimulation results in the discharge of cells in the granule cell layer.Therefore, following unilateral entorhinal lesion, the remaining contralateral entorhinal cortex extends its efferent projection to establish electrophysiologically functional synapses with the granule cells deafferented by the initial lesions.

The Hippocampus as a Model for Studying Anatomical Plasticity in the Adult Brain

The suggestion that intact axons might grow new branches (“sprout”) in response to damage of their neighbors appears to have been made at various times throughout the century-long argument that revolved around the issue of peripheral nerve regeneration. One of the earliest references was made by Haighton, who in 1795 reported a series of “physiological” studies on regeneration (or “reproduction”) which included controls for “a difficulty which naturally presents itself here, and this is, the possibility of the stomach and vocal organs having received an additional supply of nervous energy from another source” (p. 198). Exner (1885), according to Edds (1953), provided a clear description of sprouting at the neuromuscular junction, and Kennedy in his 1897 review listed several authors who mentioned the need to control for growth by undamaged nerves into deafferented sites in evaluating studies on regeneration.

Exercise alters the immune profile in Tg2576 Alzheimer mice toward a response coincident with improved cognitive performance and decreased amyloid

BackgroundInflammation is associated with Aβ pathology in Alzheimers disease (AD) and transgenic AD models. Previously, it has been demonstrated that chronic stimulation of the immune response induces pro-inflammatory cytokines IL-1β and TNF-α which contribute to neurodegeneration. However, recent evidence has shown that inducing the adaptive immune response reduces Aβ pathology and is neuroprotective. Low concentrations of IFN-γ modulate the adaptive immune response by directing microglia to differentiate to antigen presenting cells. Our objective was to determine if exercise could induce a shift from the immune profile in aged (17–19 months) Tg2576 mice to a response that reduces Aβ pathology.MethodsTG (n = 29) and WT (n = 27) mice were divided into sedentary (SED) and exercised (RUN) groups. RUN animals were provided an in-cage running wheel for 3 weeks. Tissue was harvested and hippocampus and cortex dissected out. Quantitative data was analyzed using 2 × 2 ANOVA and students t-tests.ResultsIL-1β and TNF-α were significantly greater in hippocampi from sedentary Tg2576 (TGSED) mice than in wildtype (WTSED) (p = 0.04, p = 0.006). Immune response proteins IFN-γ and MIP-1α are lower in TGSED mice than in WTSED (p = 0.03, p = 0.07). Following three weeks of voluntary wheel running, IL-1β and TNF-α decreased to levels indistinguishable from WT. Concurrently, IFN-γ and MIP-1α increased in TGRUN. Increased CD40 and MHCII, markers of antigen presentation, were observed in TGRUN animals compared to TGSED, as well as CD11c staining in and around plaques and vasculature. Additional vascular reactivity observed in TGRUN is consistent with an alternative activation immune pathway, involving perivascular macrophages. Significant decreases in soluble Aβ40 (p = 0.01) and soluble fibrillar Aβ (p = 0.01) were observed in the exercised transgenic animals.ConclusionExercise shifts the immune response from innate to an adaptive or alternative response. This shift in immune response coincides with a decrease in Aβ in advanced pathological states.

Caspase-3 activation as a bifurcation point between plasticity and cell death

Death-mediating proteases such as caspases and caspase-3 in particular, have been implicated in neurodegenerative processes, aging and Alzheimer’s disease. However, emerging evidence suggests that in addition to their classical role in cell death, caspases play a key role in modulating synaptic function. It is remarkable that active caspases-3, which can trigger widespread damage and degeneration, aggregates in structures as delicate as synapses and persists in neurons without causing acute cell death. Here, we evaluate this dichotomy, and discuss the hypothesis that caspase-3 may be a bifurcation point in cellular signaling, able to orient the neuronal response to stress down either pathological/apoptotic pathways or towards physiological cellular remodeling. We propose that temporal, spatial and other regulators of caspase activity are key determinants of the ultimate effect of caspase-3 activation in neurons. This concept has implications for differential roles of caspase-3 activation across the lifespan. Specifically, we propose that limited caspase-3 activation is critical for synaptic function in the healthy adult brain while chronic activation is involved in degenerative processes in the aging brain.

Mitochondrial Decay in the Brains of Old Rats: Ameliorating Effect of Alpha-Lipoic Acid and Acetyl-l-carnitine

To investigate the mitochondrial decay and oxidative damage resulting from aging, the activities/kinetics of the mitochondrial complexes were examined in the brains of young and old rats as well as in old rats fed R-α-lipoic acid plus acetyl-l-carnitine (LA/ALC). The brain mitochondria of old rats, compared with young rats, had significantly decreased endogenous antioxidants and superoxide dismutase activity; more oxidative damage to lipids and proteins; and decreased activities of complex I, IV and V. Complex I showed a decrease in binding affinity (increase in Km) for substrates. Feeding LA/ALC to old rats partially restored age-associated mitochondrial dysfunction to the levels of the young rats. These results indicate that oxidative mitochondrial decay plays an important role in brain aging and that a combination of nutrients targeting mitochondria, such as LA/ALC, could ameliorate mitochondrial decay through preventing mitochondrial oxidative damage.

Reactive Synaptogenesis in the Adult Nervous System

In 1885 Exner suggested that the recovery of muscular contraction observed after partial transection of a motor nerve, but prior to regeneration of the damaged fibers, resulted from collateral growth of intact fibers and reinnervation of the muscle. Subsequently Edds (1950), Hoffman (1950), and others (Weddell et al., 1946; Hones et al., 1945; Weiss and Edds, 1946) demonstrated conclusively that the transection of few motor fibers could in fact result in axon collateral sprouting by the remaining undamaged fibers. This phenomenon was extended to connections between neurons when Murray and Thompson (1957) provided direct anatomical evidence for axon collateral sprouting in the partially denervated sympathetic ganglion and Liu and Chambers (1958) reported evidence for axon sprouting in the spinal cord. Over the last 20 years there has been an explosive growth of research on axon sprouting in the central nervous system. It is now clear that the phenomenon exists and can be highly selective in terms of which fibers sprout, which neurons are reinnervated, and at what ages it can be demonstrated.

Fibril formation and neurotoxicity by a herpes simplex virus glycoprotein B fragment with homology to Alzheimer’ β amyloid peptide

Despite significant progress in the elucidation of the genetic basis of early-onset familial Alzheimers disease (AD), the etiology of sporadic cases remains elusive. Although certain genetic loci play a role in conferring susceptibility in some sporadic AD cases, it is likely that the etiology is multifactorial; hence, the majority of cases cannot be attributed to genetic factors alone, indicating that environmental factors may modulate the onset and/or progression of the disease. Head injury and infectious agents are environmental factors that have been periodically implicated, but no plausible mechanisms have been clearly identified. With regard to infectious agents, speculation has often centered on the neurotropic herpes viruses, with herpes simplex virus 1 (HSV1) considered a likely candidate. We report that an internal sequence of HSV1 glycoprotein B (gB) is homologous to the carboxyl-terminal region of the Aβ peptide that accumulates in diffuse and neuritic plaques in AD. Synthetic peptides were g...

Caspase-Cleaved Tau Accumulation in Neurodegenerative Diseases Associated with Tau and α-Synuclein Pathology

Alzheimer’s disease (AD), Pick’s disease (PiD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and dementia with Lewy bodies (DLB) are diseases associated with the accumulation of tau or α-synuclein. In AD, β-amyloid (Aβ)-associated caspase activation and cleavage of tau at Asp421 (ΔTau) may be an early step in neurofibrillary tangle (NFT) formation. To examine whether ΔTau accumulates in other diseases not characterized by extracellular Aβ accumulation, we examined PiD, PSP, and CBD cases in comparison to those without extensive tau accumulation including frontotemporal lobar degeneration without Pick bodies (FTLD) and control cases. Additionally, we studied ΔTau accumulation in DLB cases associated with intracellular α-synuclein. ΔTau was observed in all disease cases except non-PiD FTLD and controls. These results demonstrate that the accumulation of ΔTau may represent a common pathway associated with abnormal accumulation of intracellular tau or α-synuclein and may be relatively less dependent on the extracellular accumulation of Aβ in non-AD dementias.