With regard to a possible genetic contribution of TDP-43 to FTLD-U, our group reported negative results in Salzburg. We conducted a high-density genetic association and linkage disequilibrium mapping analysis to investigate whether common variations at the TDP-43 locus act as a risk factor for disease in the Manchester FTLD cohort. Among 214 patients not harboring a tau or progranulin mutation, who were clinically diagnosed as having either FTD, FTD with motor neuron disease, semantic dementia, or related disorders, we observed no significant SNP or haplotype association (Rollinson et al., 2007, in press). These data suggest that common variations do not increase genetic risk in our population, but it leaves open the possibility of rare mutations yet to be found.

View all comments by Stuart Pickering-Brown

These papers represent exciting work describing a new genetic mutation associated with familial ALS. The results further highlight the importance for RNA processing in at least familial forms of motor neuron disease. Much work remains to determine the exact mechanisms by which FUS modulates motor neuron survival. It may be related to that of TDP-43. However, the lack of cytoplasmic aggregation of TDP-43, and rare ubiquitin inclusions in the patients with FUS mutations, suggest the mechanisms may be distinct. It is interesting that FUS protein did not accumulate in the cytoplasm of motor neurons in sporadic ALS patients, again suggestive that the pathogenic mechanisms of mutant FUS-induced motor neuron degeneration may be distinct from that in sporadic ALS.

View all comments by Robert Bowser

These studies raise interesting questions about whether one problem in ALS and perhaps other neurodegenerative diseases is that RNA trafficking proteins fail to properly deliver RNAs to dendritic spines. The paper by Kwiatkowski et al. reports evidence that wild-type FUS and TDP-43 may be involved in transporting RNA into dendrites, where it mediates local protein synthesis that can be stimulated by neural activity. The clumping of the mutant form described by both new papers could therefore perturb the transport of RNA. Local protein synthesis in dendrites plays a major role in the activity-dependent modulation of synaptic strength. Changes in synaptic activity have been recently reported in the mouse model of SOD1 mutation (van Zundert et al., 2008), so it will be worthwhile to examine this issue in the FUS mice that will certainly be developed by these investigators.

View all comments by Eric Frank

This is an extremely exiting story in the understanding of ALS pathogenesis. It actually it dates back to 1998—with the first description of mRNA processing errors in sporadic ALS (Lin et al., 1998), which, interestingly, was made not in the SOD1 mouse model. At the same time, the spinal muscular atrophy gene was discovered. SMA is not unlike a childhood ALS, though predominately lower motor neurons are affected in that disease. The SMA gene defect is involved in RNA metabolism. So for the next 10 years, the SMA field has investigated the pathobiology of the defective protein. At the time it made the link between sporadic ALS and the SMA story intriguing. But there was no clear genetic link (or cause for the changes in sporadic ALS).

Feed forward to 2008, when Chris Shaw and others found a true genetic defect in RNA metabolism-based protein TDP-43. (Of course more work needs to be done on that.) And now another gene by the Shaw group, and now verified by the group in Boston, does set a string of targets that all focus on RNA...  Read more

This is an extremely exiting story in the understanding of ALS pathogenesis. It actually it dates back to 1998—with the first description of mRNA processing errors in sporadic ALS (Lin et al., 1998), which, interestingly, was made not in the SOD1 mouse model. At the same time, the spinal muscular atrophy gene was discovered. SMA is not unlike a childhood ALS, though predominately lower motor neurons are affected in that disease. The SMA gene defect is involved in RNA metabolism. So for the next 10 years, the SMA field has investigated the pathobiology of the defective protein. At the time it made the link between sporadic ALS and the SMA story intriguing. But there was no clear genetic link (or cause for the changes in sporadic ALS).

Feed forward to 2008, when Chris Shaw and others found a true genetic defect in RNA metabolism-based protein TDP-43. (Of course more work needs to be done on that.) And now another gene by the Shaw group, and now verified by the group in Boston, does set a string of targets that all focus on RNA metabolism and (lower) motor neurons.

By the way, all these cases appear to predominately involve a lower motor neuron form of ALS. The hint from genetics does suggest more of a loss of function rather than gain, but cell biology will ultimately sort that out. We certainly await the generation of mouse or fly models, which are now well underway for TDP-43. However, this may be a particularly difficult target for specific, non-toxic drug therapy.

View all comments by Jeffrey D. Rothstein

These back-to-back papers on the identification of FUS (fused in sarcoma) gene as a new genetic component of ALS open a new era of research and direct our attention to mRNA biology with respect to disease. After the first identification of mRNA processing errors in ALS patients (Lin, Bristol et al., 1998), the discovery of TDP-43 (Neumann, Sampathu et al., 2006) and now the FUS gene clearly indicate the importance of mRNA management in neurodegenerative diseases. Defects in RNA transcription, splicing, and trafficking may be the reason for cell-type-specific degeneration of motor neurons in ALS. Motor neurons both in the cortex and spinal cord are very large excitatory neurons that extend long axons to their targets and require high levels of energy and protein integrity for survival and function. Defects in transcriptional mechanisms may result in splicing defects, which could give rise to formation of non-functional proteins that would deplete the pool of required proteins for cellular function, and these non-functional proteins may form aggregates that are toxic to neurons. In...  Read more

These back-to-back papers on the identification of FUS (fused in sarcoma) gene as a new genetic component of ALS open a new era of research and direct our attention to mRNA biology with respect to disease. After the first identification of mRNA processing errors in ALS patients (Lin, Bristol et al., 1998), the discovery of TDP-43 (Neumann, Sampathu et al., 2006) and now the FUS gene clearly indicate the importance of mRNA management in neurodegenerative diseases. Defects in RNA transcription, splicing, and trafficking may be the reason for cell-type-specific degeneration of motor neurons in ALS. Motor neurons both in the cortex and spinal cord are very large excitatory neurons that extend long axons to their targets and require high levels of energy and protein integrity for survival and function. Defects in transcriptional mechanisms may result in splicing defects, which could give rise to formation of non-functional proteins that would deplete the pool of required proteins for cellular function, and these non-functional proteins may form aggregates that are toxic to neurons. In addition, defects in the trafficking of mRNA may lead to depletion of key proteins that are in high demand locally for motor neuron function. But if FUS has a general function in mRNA transcription, splicing, and trafficking, why do mutations in this gene cause ALS and not other neurodegenerative diseases? What makes motor neurons more vulnerable in the presence of defective FUS? It could be true that in motor neurons FUS controls the transcription of a distinct set of mRNA that is expressed in a cell-type-specific manner in motor neurons, or that FUS controls the production of a key protein that is highly required in motor neurons when compared to other cell-types, and thus motor neurons may become vulnerable first. FUS seems to be the tip of the iceberg. Finding effectors, binding partners including mRNA, may lead to the identification of key components of both familial and sporadic ALS. More work is on the way!

References:

Kneussel M. Dynamic regulation of GABA(A) receptors at synaptic sites. Brain Res Brain Res Rev. 2002 Jun ;39(1):74-83. Abstract

Lin CL, Bristol LA, Jin L, Dykes-Hoberg M, Crawford T, Clawson L, Rothstein JD. Aberrant RNA processing in a neurodegenerative disease: the cause for absent EAAT2, a glutamate transporter, in amyotrophic lateral sclerosis. Neuron. 1998 Mar;20(3):589-602. Abstract

Neumann M, Sampathu DM, Kwong LK, Truax AC, Micsenyi MC, Chou TT, Bruce J, Schuck T, Grossman M, Clark CM, McCluskey LF, Miller BL, Masliah E, Mackenzie IR, Feldman H, Feiden W, Kretzschmar HA, Trojanowski JQ, Lee VM. Ubiquitinated TDP-43 in frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Science. 2006 Oct 6;314(5796):130-3. Abstract

Vance C, Rogelj B, Hortobágyi T, De Vos KJ, Nishimura AL, Sreedharan J, Hu X, Smith B, Ruddy D, Wright P, Ganesalingam J, Williams KL, Tripathi V, Al-Saraj S, Al-Chalabi A, Leigh PN, Blair IP, Nicholson G, de Belleroche J, Gallo JM, Miller CC, Shaw CE. Mutations in FUS, an RNA processing protein, cause familial amyotrophic lateral sclerosis type 6. Science. 2009 Feb 27;323(5918):1208-11. Abstract

View all comments by P. Hande Ozdinler

This study characterizes the dynamic behavior of SOD1 in detail. First, it essentially reproduces previous studies including the ones from the authors' group, as it has been well known that overall structures are similar between wild-type and mutant SOD1 proteins. In addition, significant differences in the dynamic behavior have been observed between Apo and holo forms of SOD1. When the metal ions are removed from the protein, structural disorder increases particularly in the loop regions.

We think that one of the interesting findings in this paper is the increased solvent accessibility of Cys-6 upon metal removal. Cys-6 is one of the four Cys residues (Cys-6, 57, 111, 146) in SOD1 and is buried toward the protein interior in the holo form of SOD1. In an enzymatically active form of SOD1, an intra-molecular disulfide forms between Cys-57 and 146, while Cys-6 and 111 remain reduced. In contrast, pathological inclusions purified from several ALS-model mice contain SOD1 multimers that are cross-linked via non-physiological disulfide bonds (  Read more

This study characterizes the dynamic behavior of SOD1 in detail. First, it essentially reproduces previous studies including the ones from the authors' group, as it has been well known that overall structures are similar between wild-type and mutant SOD1 proteins. In addition, significant differences in the dynamic behavior have been observed between Apo and holo forms of SOD1. When the metal ions are removed from the protein, structural disorder increases particularly in the loop regions.

We think that one of the interesting findings in this paper is the increased solvent accessibility of Cys-6 upon metal removal. Cys-6 is one of the four Cys residues (Cys-6, 57, 111, 146) in SOD1 and is buried toward the protein interior in the holo form of SOD1. In an enzymatically active form of SOD1, an intra-molecular disulfide forms between Cys-57 and 146, while Cys-6 and 111 remain reduced. In contrast, pathological inclusions purified from several ALS-model mice contain SOD1 multimers that are cross-linked via non-physiological disulfide bonds (Furukawa et al., 2006).

It is, however, still controversial which Cys residues are involved in the formation of cross-linked SOD1 multimers under pathological conditions. While we have previously reported that the disulfide formation is not absolutely required for triggering SOD1 aggregation (Furukawa et al., 2008), an important role of Cys-6 and 111 in the formation of disulfide cross-links has been also suggested in the cultured cell model (Niwa et al., 2007). In addition, ALS-causing mutations at position 6 have been reported (i.e., C6G and C6F), implying that the other Cys residues are involved in the formation of disulfide-linked multimers even when Cys-6 is unavailable for disulfide formation. Nonetheless, the increased flexibility and solvent accessibility of Cys-6 upon metal removal will be an important clue to explain a molecular mechanism of the pathological SOD1 oligomer formation.

View all comments by Yoshiaki Furukawa

This study elegantly gives a first insight on a transgenic mouse model of mutant TDP-43 (A315T) identified in familial ALS patients. For those in the field, it is clear that generating these mouse models is a mammoth task on its own. Among the many interesting findings in this paper, the first to catch my attention was that the 25-kDa TDP-43 C-terminal fragments (CTFs) were recovered from detergent-soluble fractions but not from urea fractions as observed in sporadic and familial ALS/FTLD patients. If the TDP-43 25-kDa CTFs would indeed be confirmed as the real culprit, this would yet again emphasize the importance of soluble but not aggregated protein/peptide in cellular toxicity, as has been shown for a number of other proteinopathies including Aβ, α-synuclein, polyglutamine expansion in Huntingtin, and mutant SOD1.

Another important observation made in this paper was that ubiquitin-immunoreactive (ir) inclusions observed in select neurons including motor neurons were not TDP-43-ir. Thus, the mutant TDP-43 (A315T) mice do not completely model ALS, where...  Read more

This study elegantly gives a first insight on a transgenic mouse model of mutant TDP-43 (A315T) identified in familial ALS patients. For those in the field, it is clear that generating these mouse models is a mammoth task on its own. Among the many interesting findings in this paper, the first to catch my attention was that the 25-kDa TDP-43 C-terminal fragments (CTFs) were recovered from detergent-soluble fractions but not from urea fractions as observed in sporadic and familial ALS/FTLD patients. If the TDP-43 25-kDa CTFs would indeed be confirmed as the real culprit, this would yet again emphasize the importance of soluble but not aggregated protein/peptide in cellular toxicity, as has been shown for a number of other proteinopathies including Aβ, α-synuclein, polyglutamine expansion in Huntingtin, and mutant SOD1.

Another important observation made in this paper was that ubiquitin-immunoreactive (ir) inclusions observed in select neurons including motor neurons were not TDP-43-ir. Thus, the mutant TDP-43 (A315T) mice do not completely model ALS, where ubiquitin-ir inclusions are also TDP-43-ir; nevertheless, this work does lead to a very interesting question: what are these inclusions composed of?

Knowing earlier studies (see Tatom et al., 2009 and ARF related news story), I am also not surprised at the glaring omission of wild-type TDP-43 mice as a better control than the non-transgenic mice utilized in this study. So although clearly not all is answered yet, let's see how these and other TDP-43 mouse models currently being developed will unfold the mysteries of TDP-43-led neurodegeneration.

View all comments by Samir Kumar-Singh

This important study establishes for the first time a genetic risk factor for sporadic ALS, thus providing a long-sought entry point into mechanisms and genetics of ALS. Genetic risk factors for neurodegenerative diseases will likely lead to novel insights into mechanisms of disease.

The impact of the chromogranin B mutations is slightly lower than that of the ApoE4 allele in Alzheimer disease. Because the chromogranin B mutations had an impact on onset time in familial ALS, and on risk of disease in sporadic ALS, the findings provide important support for the notion that sporadic and familial ALS are mechanistically related.

Chromogranin has been linked to mutant SOD1 by two previous studies. A frequently raised question is to what extent SOD1-based ALS mice are relevant in mimicking human disease. The association to chromogranin B in the SOD1 mouse model and now patient cohorts for both sporadic and familial ALS strongly supports the notion of converging cellular and molecular mechanisms of disease.

One important implication for scientists working on ALS is that the...  Read more

This important study establishes for the first time a genetic risk factor for sporadic ALS, thus providing a long-sought entry point into mechanisms and genetics of ALS. Genetic risk factors for neurodegenerative diseases will likely lead to novel insights into mechanisms of disease.

The impact of the chromogranin B mutations is slightly lower than that of the ApoE4 allele in Alzheimer disease. Because the chromogranin B mutations had an impact on onset time in familial ALS, and on risk of disease in sporadic ALS, the findings provide important support for the notion that sporadic and familial ALS are mechanistically related.

Chromogranin has been linked to mutant SOD1 by two previous studies. A frequently raised question is to what extent SOD1-based ALS mice are relevant in mimicking human disease. The association to chromogranin B in the SOD1 mouse model and now patient cohorts for both sporadic and familial ALS strongly supports the notion of converging cellular and molecular mechanisms of disease.

One important implication for scientists working on ALS is that the research mechanistically links SOD1 mutations to a set of mutations in chromogranin B. We now have potentially interacting mutations in two genes to study; this will likely lead to new disease models and hopefully to first elements of a molecular disease pathway. It will be interesting to determine whether there is a relationship between mutant SOD1 secretion and chromogranin B mutations. Should this be the case, it may suggest that the risk involves local secretion of misfolded proteins such as mutant SOD1. Of further interest are the implications for the role of ER stress pathways in the pathogenesis of ALS.

It will be important to determine whether other genes implicated in ALS (including the RNA metabolism genes TDP-43 and FUS) also synergize with chromogranin B mutations to promote disease. Whether chromogranin A variants link to ALS is definitely worth investigating as well.

View all comments by Pico Caroni

In addition to the traditional funding models mentioned in this story, we would like to also mention a new funding model available for ALS research. Prize4Life is a nonprofit organization that awards two prizes of $1 million each (the ALS Biomarker Challenge and the ALS Treatment Prize). Instead of recognizing historical accomplishments, Prize4Life designs prizes that we believe are achievable in a two- to three-year timeframe and then recruits teams to compete. Prize competitions have been steadily gaining traction in a variety of domains of innovation because their emphasis on specific outcomes has the capacity to propel a field forward very quickly, and can attract creative thinking from both within a field and “outside the box.” For example, in 2009 Prize4Life awarded two $50,000 Milestone Prizes, one of which went to an established ALS researcher, and one of which went to a trained dermatologist who explored a completely novel approach towards an ALS biomarker. Visit Prize4Life to learn more or to register to compete for a...  Read more

In addition to the traditional funding models mentioned in this story, we would like to also mention a new funding model available for ALS research. Prize4Life is a nonprofit organization that awards two prizes of $1 million each (the ALS Biomarker Challenge and the ALS Treatment Prize). Instead of recognizing historical accomplishments, Prize4Life designs prizes that we believe are achievable in a two- to three-year timeframe and then recruits teams to compete. Prize competitions have been steadily gaining traction in a variety of domains of innovation because their emphasis on specific outcomes has the capacity to propel a field forward very quickly, and can attract creative thinking from both within a field and “outside the box.” For example, in 2009 Prize4Life awarded two $50,000 Milestone Prizes, one of which went to an established ALS researcher, and one of which went to a trained dermatologist who explored a completely novel approach towards an ALS biomarker. Visit Prize4Life to learn more or to register to compete for a prize.

View all comments by Meghan Kallman

Regarding the statement in this news story "De Belleroche also pointed out that a DAO mutant mouse might be a useful model for ALS research, which sorely needs new models," I'd like to note that it is unlikely that loss of DAO alone will be sufficient for disease. A line of DAO mutant mice, essentially devoid of DAO activity, has been around almost 30 years (Konno and Yakumura, 1983) without any ALS-like symptoms reported in the first year of life. Here is a quote from that paper:

"No apparent difference was detected between DAO+ and DAO- mice. The DAO- mice grew and behaved normally. They were fertile and produced as many offspring as the DAO+ animals did. Besides, the unilaterally nephrectomized DAO- mice lived more than 1 year without any impairment of health. ...[T]he discovery of the DAO- mice suggests that the enzyme is not essential, at least for the growth and reproduction of the mouse under laboratory conditions."

References:
Konno R, Yasumura Y. 1983. Mouse mutant deficient in D-amino acid oxidase activity. Genetics 103:277-85. Abstract

View all comments by Steve Barger