Ralph M. Garruto

Pathological TDP-43 in parkinsonism–dementia complex and amyotrophic lateral sclerosis of Guam

Pathological TDP-43 is the major disease protein in frontotemporal lobar degeneration characterized by ubiquitin inclusions (FTLD-U) with/without motor neuron disease (MND) and in amyotrophic lateral sclerosis (ALS). As Guamanian parkinsonism–dementia complex (PDC) or Guamanian ALS (G-PDC or G-ALS) of the Chamorro population may present clinically similar to FTLD-U and ALS, TDP-43 pathology may be present in the G-PDC and G-ALS. Thus, we examined cortical or spinal cord samples from 54 Guamanian subjects for evidence of TDP-43 pathology. In addition to cortical neurofibrillary and glial tau pathology, G-PDC was associated with cortical TDP-43 positive dystrophic neurites and neuronal and glial inclusions in gray and/or white matter. Biochemical analyses showed the presence of FTLD-U-like insoluble TDP-43 in G-PDC, but not in Guam controls (G-C). Spinal cord pathology of G-PDC or G-ALS was characterized by tau positive tangles as well as TDP-43 positive inclusions in lower motor neurons and glial cells. G-C had variable tau and negligible TDP-43 pathology. These results indicate that G-PDC and G-ALS are associated with pathological TDP-43 similar to FTLD-U with/without MND as well as ALS, and that neocortical or hippocampal TDP-43 pathology distinguishes controls from disease subjects better than tau pathology. Finally, we conclude that the spectrum of TDP-43 proteinopathies should be expanded to include neurodegenerative cognitive and motor diseases, affecting the Chamorro population of Guam.

CAN THE MECHANISMS OF ALUMINUM NEUROTOXICITY BE INTEGRATED INTO A UNIFIED SCHEME

Regardless of the host, the route of administration, or the speciation, aluminum is a potent neurotoxicant. In the young adult or developmentally mature host, the neuronal response to Al exposure can be dichotomized on morphological grounds. In one, intraneuronal neurofilamentous aggregates are formed, whereas in the other, significant neurochemical and neurophysiological perturbations are induced without neurofilamentous aggregate formation. Evidence is presented that the induction of neurofilamentous aggregates is a consequence of alterations in the posttranslational processing of neurofilament (NF), particularly with regard to phosphorylation state. Although Al has been reported to impact on gene expression, this does not appear to be critical to the induction of cytoskeletal pathology. In hosts responding to Al exposure without the induction of cytoskeletal pathology, impairments in glucose utilization, agonist-stimulated inositol phosphate accumulation, free radical-mediated cytotoxicity, lipid peroxidation, reduced cholinergic function, and altered protein phosphorylation have been described. The extent to which these neurochemical modifications correlate with the induction of a characteristic neurobehavioral state is unknown. In addition to these paradigms, Al is toxic in the immediate postnatal interval. Whether unique mechanisms of toxicity are involved during development remains to be determined. In this article, the mechanisms of Al neurotoxicity are reviewed and recommendations are put forth with regard to future research. Primary among these is the determination of the molecular site of Al toxicity, and whether this is based on Al substitution for divalent metals in a number of biological processes. Encompassed within this is the need to further understand the genesis of host- and developmental-specific responses.

Altered functional properties of a TRPM2 variant in Guamanian ALS and PD

Two related neurodegenerative disorders, Western Pacific amyotrophic lateral sclerosis (ALS) and parkinsonism–dementia (PD), originally occurred at a high incidence on Guam, in the Kii peninsula of Japan, and in southern West New Guinea more than 50 years ago. These three foci shared a unique mineral environment characterized by the presence of severely low levels of Ca2+ and Mg2+, coupled with high levels of bioavailable transition metals in the soil and drinking water. Epidemiological studies suggest that genetic factors also contribute to the etiology of these disorders. Here, we report that a variant of the transient receptor potential melastatin 2 (TRPM2) gene may confer susceptibility to these diseases. TRPM2 encodes a calcium-permeable cation channel highly expressed in the brain that has been implicated in mediating cell death induced by oxidants. We found a heterozygous variant of TRPM2 in a subset of Guamanian ALS (ALS-G) and PD (PD-G) cases. This variant, TRPM2P1018L, produces a missense change in the channel protein whereby proline 1018 (Pro1018) is replaced by leucine (Leu1018). Functional studies revealed that, unlike WT TRPM2, P1018L channels inactivate. Our results suggest that the ability of TRPM2 to maintain sustained ion influx is a physiologically important function and that its disruption may, under certain conditions, contribute to disease states.

Tau pathology involves protein phosphatase 2A in Parkinsonism-dementia of Guam

Significance Parkinsonism-dementia (PD) of Guam is a classical tauopathy in which abnormal hyperphosphorylation of tau leads to neurodegeneration and dementia. A key unresolved question is the mechanism of abnormal hyperphosphorylation of tau in this disease. This study reports the involvement of a signaling pathway in which the inhibition of protein phosphatase 2A (PP2A) through phosphorylation of its catalytic subunit PP2Ac at Tyr307 induced by the activation of metabotropic glutamate receptor 5 (mGluR5) leads to hyperphosphorylation of tau. These findings suggest that the mGluR5–PP2A axis has a central role in neurofibrillary degeneration in Guam PD and thus may be a therapeutic target for the treatment of this disease and related tauopathies. Parkinsonism-dementia (PD) of Guam is a neurodegenerative disease with parkinsonism and early-onset Alzheimer-like dementia associated with neurofibrillary tangles composed of hyperphosphorylated microtubule-associated protein, tau. β-N-methylamino-l-alanine (BMAA) has been suspected of being involved in the etiology of PD, but the mechanism by which BMAA leads to tau hyperphosphorylation is not known. We found a decrease in protein phosphatase 2A (PP2A) activity associated with an increase in inhibitory phosphorylation of its catalytic subunit PP2Ac at Tyr307 and abnormal hyperphosphorylation of tau in brains of patients who had Guam PD. To test the possible involvement of BMAA in the etiopathogenesis of PD, we studied the effect of this environmental neurotoxin on PP2A activity and tau hyperphosphorylation in mouse primary neuronal cultures and metabolically active rat brain slices. BMAA treatment significantly decreased PP2A activity, with a concomitant increase in tau kinase activity resulting in elevated tau hyperphosphorylation at PP2A favorable sites. Moreover, we found an increase in the phosphorylation of PP2Ac at Tyr307 in BMAA-treated rat brains. Pretreatment with metabotropic glutamate receptor 5 (mGluR5) and Src antagonists blocked the BMAA-induced inhibition of PP2A and the abnormal hyperphosphorylation of tau, indicating the involvement of an Src-dependent PP2A pathway. Coimmunoprecipitation experiments showed that BMAA treatment dissociated PP2Ac from mGluR5, making it available for phosphorylation at Tyr307. These findings suggest a scenario in which BMAA can lead to tau pathology by inhibiting PP2A through the activation of mGluR5, the consequent release of PP2Ac from the mGluR5–PP2A complex, and its phosphorylation at Tyr307 by Src.

Concentrations of Cd, Co, Cu, Fe, Mn, Rb, V, and Zn in Formalin-Fixed Brain Tissue in Amyotrophic Lateral Sclerosis and Parkinsonism-Dementia Complex of Guam Determined by High-Resolution ICP-MS

Amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia complex (PDC) are neurodegenerative disorders that occurred with extremely high frequency among the native population on Guam, especially in the 1950s and 1960s, but have substantially declined over the last half-century. The etiology of these diseases is unknown, but the most plausible hypothesis centers on imbalances in essential and toxic metals. We have determined the concentrations of Cd, Co, Cu, Fe, Mn, Rb, V, and Zn in formalin-fixed brain tissue collected during the period 1979–1983 from eight Guamanian patients with ALS, four with PDC, and five control subjects using high-resolution inductively coupled plasma-mass spectrometry. The concentrations of Cd are markedly and significantly elevated both in gray and white matter in ALS, but not in PDC patients. The concentrations of Zn are elevated for both patient groups, in both gray and white matter, but only the difference in gray matter for PDC is significant. For the other metals, no significant differences are found.

Current pathways for epidemiological research in amyotrophic lateral sclerosis.

Abstract Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disease. The current status of the epidemiology, challenges to its study, and novel study design options are discussed in this paper. We focus on recent results from large-scale population based prospective studies, case-control studies and population based registries, risk factors, and neuropathologic findings in chronic traumatic encephalomyelopathy. We identify areas of interest for future research, including time-trends in the incidence and prevalence of ALS; the meaning of lifetime risk; the phenotypic description of ALS; the definition of familial versus sporadic ALS, syndromic aspects of ALS; specific risk factors such as military service, life style factors such as smoking, the use of statins, and the presence of β-N-methylamino-L-alanine (BMAA), an excitotoxic amino acid derivative possibly produced by cyanobacteria found in almost every terrestrial and aquatic habitat; the emergence and disappearance of an endemic ALS in areas of the Pacific; and gene-environment interactions in the etiology of ALS. To move the epidemiology forward, we suggest using well-characterized cohorts of newly diagnosed ALS patients to identify risk and prognostic factors; storing biological material for future studies; building on the National ALS Registry as a resource of future studies; working in multidisciplinary consortia; and addressing the possible early life etiology of ALS.

Growth of Qinghai Tibetans living at three different high altitudes

This study compares the stature, weight, skinfolds, upper arm muscle area, and chest dimensions of Tibetan children, adolescents, and young adults who were born and raised, or who had lived from infancy, at 3,200 m, 3,800 m, and 4,300 m in Qinghai Province, Peoples Republic of China. While the individuals measured in Qinghai are among the tallest and heaviest Tibetans reported in the literature, they are nevertheless smaller and lighter than well-off children living at low altitude. The pattern of size variation among Tibetan males and females measured at the three high altitudes, along with evidence of a secular trend at 4,300 m, suggests that nutrition may significantly effect growth at high altitude. Only minor differences in thorax dimensions exist between Tibetan males and females measured at 3,200 m and 3,800 m. However, Tibetan males at 4,300 m possess slightly narrower and deeper chests (during and after adolescence) than males at 3,200 m and 3,800 m. Since individuals from 3,800 m and 4,300 m belong to the same local populations, this characteristic is unlikely to be genetically determined. However, it may be related to differences in the degree of hypoxia or to the influences of other environmental conditions.

The Cu/Zn superoxide dismutase gene in ALS and parkinsonism-dementia of Guam.

Guam is one of three endemic foci whose indigenous (Chamorro) people have an unusually high incidence of fatal neurodegenerative disorders, amyotrophic lateral sclerosis (ALS) and Parkinsonism-dementia (PD). Recently, mutations in the Cu/Zn superoxide dismutase (SOD-1) gene have been identified in some familial cases of ALS. To investigate if mutations in the SOD-1 gene are also involved in the pathogenesis of ALS and PD of Guam, we analyzed the SOD-1 gene in Chamorros. No mutations were found in Chamorros with ALS or PD, indicating that mutations in the SOD-1 gene do not underlie the high-incidence neurodegenerative disorders of Guam.

Failure to isolate human T cell lymphotropic virus type I and to detect variant-specific genomic sequences by polymerase chain reaction in Melanesians with indeterminate western immunoblot.

The controversy over the endemicity of human T cell lymphotropic virus type I (HTLV-I) in Melanesia has been settled recently by the isolation of genetically distinct, highly divergent sequence variants of HTLV-I from unrelated inhabitants of Papua New Guinea and the Solomon Islands. Still at issue, however, is the significance of the high frequency of indeterminate HTLV-I Western blots (defined as reactivity to only gag-encoded proteins) among Melanesians. To investigate whether this indeterminate seroreactivity reflects specific reactivity to the Melanesian HTLV-I variants, 27 seroindeterminate Melanesians from Papua New Guinea and the Solomon Islands were studied for evidence of HTLV-I infection. Although antibodies against Melanesian variant-specific env gene products and variant-specific env gene sequences were detected by Western blot analysis and polymerase chain reaction, respectively, in all 11 HTLV-I Western blot-positive Melanesians, none of the 27 seroindeterminate Melanesians had such variant-specific antibodies or HTLV-I proviral sequences. In addition, attempts to isolate HTLV-I from seroindeterminate individuals were unsuccessful. These data indicate that HTLV-I infection is not the cause of the indeterminate Western blot reactivity seen in Melanesia.

Identification of novel susceptibility loci for Guam neurodegenerative disease: Challenges of genome scans in genetic isolates

Amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) is a fatal neurodegenerative disease found in the Chamorro people of Guam and other Pacific Island populations. The etiology is unknown, although both genetic and environmental factors appear important. To identify loci for ALS/PDC, we conducted both genome-wide linkage and association analyses, using approximately 400 microsatellite markers, in the largest sample assembled to date, comprising a nearly complete sample of all living and previously sampled deceased cases. A single, large, complex pedigree was ascertained from a village on Guam, with smaller families and a case-control sample ascertained from the rest of Guam by population-based neurological screening and archival review. We found significant evidence for two regions with novel ALS/PDC loci on chromosome 12 and supportive evidence for the involvement of the MAPT region on chromosome 17. D12S1617 on 12p gave the strongest evidence of linkage (maximum LOD score, Z(max) = 4.03) in our initial scan, with additional support in the complete case-control sample in the form of evidence of allelic association at this marker and another nearby marker. D12S79 on 12q also provided significant evidence of linkage (Z(max) = 3.14) with support from flanking markers. Our results suggest that ALS/PDC may be influenced by as many as three loci, while illustrating challenges that are intrinsic in genetic analyses of isolated populations, as well as analytical strategies that are useful in this context. Elucidation of the genetic basis of ALS/PDC should improve our understanding of related neurodegenerative disorders including Alzheimer disease, Parkinson disease, frontotemporal dementia and ALS.