SOD1, Tau Swept Up in Prion-like Biology during ALS Meeting

January 16, 2016 - als

The initial external pointer of amyotrophic together sclerosis (ALS) customarily crops adult in one spot: a tiny difficulty swallowing, or debility in one leg or one arm. Then it spreads. Scientists now think a underlying pathogenic proteins, such as SOD1, competence pave a approach for this sign widespread in prion-like fashion, roving from neuron to neuron and converting good protein to bad. This was a vital thesis during a International Symposium on ALS/MND hold Dec 11-13 in Orlando, Florida. Adopting injection seeding paradigms that have prolonged been used in prion research, researchers find parallels between a constructional variants of proteins concerned in neurodegeneration, such as SOD1 and tau, and a “strains” of varying pathogenicity in prion biology. Importantly, scientists were not going so distant as to call ALS a prion disease, according to Brian Dickie of a Motor Neurone Disease Association in a United Kingdom, that orderly a conference. All a same, if ALS is driven by a prion-like mechanism, afterwards treatments should be means to hindrance a progression, he speculated. Some speakers offering rough ideas about how to find and exam such therapeutics.

Pass it on. SOD1 aggregates in mice injected with hankie homogenates containing a SOD1-G93A “strain” (right), though not aegis (left) or homogenates from SOD1-G85R mice (center). [Courtesy of Acta Neuropathologica/Springer (Jan 2016, Vol 131, Issue 1, pp 103-114).]  

SOD1 Gets a Move On
Jacob Ayers of a University of Florida in Gainesville described strain-like properties of SOD1 he rescued during his efforts to follow SOD1 delivery in vivo (Ayers et al., 2014). As models, he used mice heterozygous for a ALS-associated tellurian SOD1 various G85R. He tracked a chronicle of SOD1 G85R fused to yellow fluorescent protein (YFP) to see if a protein many-sided in vivo (see Jan 2009 news). These heterozygous mice do not rise engine neuron illness on their own. However, their genotype somehow done them exposed to a widespread of poisonous forms of SOD triggered by seeding injection experiments, compared to mice expressing customarily wild-type SOD1.

Ayers injected baby mice intrathecally with spinal cord homogenate from inept adult mice expressing poisonous SOD1-G93A or G37R, dual other ALS-linked variants. Six of 10 G85R mice injected with SOD1-G93A grown stoppage in their rear limbs between 3 and 11 months of age. Animal autopsy, aka necropsy, suggested punctate yellow SOD1 aggregates in a neurons of a spinal cord, brainstem, and thalamus. When Ayers injected homogenates from these animals into 4 new SOD1-G85R-YFP mice, illness occurred even sooner, with all animals building transformation problems within 3 months. In contrast, non-transgenic mice, or mice expressing wild-type tellurian SOD1, that were injected with SOD1-G93A homogenates seemed normal, as did G85R-YFP animals injected with homogenates from non-transgenic mice.

The commentary prove that passaging poisonous SOD1 variants by animals expressing G85R can modify this differently amiable various into a some-more pathogenic strain. That aria afterwards some-more straightforwardly corrupts additional molecules of G85R SOD1.

This accelerated delivery in a second thoroughfare mimics a materialisation of horde instrumentation seen in prion biology, in that a illness transmits some-more fast between proteins matching in sequence, Ayers pronounced (Aguzzi et al., 2007; Bruce et al., 1994). With prions, a judgment customarily refers to send between animals of a same contra opposite species; in this box it relates to a SOD1 genotype of the mice.

Ayers saw opposite formula with a G37R and a G93A SOD1 variant. Even after some-more than 13 months, SOD1-G85R-YFP injected with homogenates from G37R animals grown no signs of engine neuron disease. In prion terms, SOD1-G93A and G37R would be deliberate opposite strains, Ayers pointed out.

In a investigate published final month, Ayers reported how SOD1 misfolding widespread around a mouse’s shaken complement following injection into a rear prong sciatic nerves of adult mice. In this case, he initial injected homogenates from G93A mice intrathecally into SOD1-G85R heterozygotes. When these animals became inept he used their hankie to make new homogenates that he injected directly into a sciatic nerves of a new collection of G85R mice. Aggregates seemed initial in feeling neurons in a dorsal base ganglion on a injected side of a body, and from there widespread to a contralateral dorsal base ganglion, spinal cord, and brain. In parallel, a mice mislaid strength initial in a injected leg, afterwards in a other. Within a month of a injection, both rear legs were inept (Ayers et al., 2016). 

The formula paint a “grand slam,” commented Neil Cashman of a University of British Columbia in Vancouver, Canada, who did not attend in a project. “They have been means to rise a credible, in vivo indication of SOD1-propagated misfolding, accompanied by paralysis,” Cashman said. SOD1-G85 seems to act as a arrange of “acceptor” for SOD1-propagated misfolding in a approach that a wild-type protein does not. Cashman speculated that in an aging person, wild-type SOD1 competence spin some-more disposed to templated misfolding over time. This competence be due to changes in proteostasis that leave it somewhat folded, or as a monomer instead of a healthy dimer form, he theorized. This propagation contrasts a miss of pathology widespread in other ALS models shaped on entire SOD1 transgene expression, Cashman noted. Ayers suggested that scientists could exam therapeutics in mice injected with second-passage homogenates.

Edward Pokrishevsky, in Cashman’s group, also had therapeutics in mind. Pokrishevsky grown a high-throughput assay, shaped on a beliefs of poisonous protein propagation described by Ayers, and used it to shade for probable blockers of SOD1 misfolding and propagation. In HEK293 cells, Pokrishevsky co-expressed SOD1-G85R tagged with immature fluorescent protein (GFP), and another more-toxic chronicle of SOD1, such as a truncation mutant G127X. Alone, SOD1-G85R-GFP seemed diffuse, though in a participation of a second poisonous SOD1 it many-sided in 20 percent to 30 percent of cells. Pokrishevsky reasoned that drugs that forestall SOD1 propagation should strengthen SOD1-G85R from aggregation, and could so be identified in his assay

The researchers have not nonetheless started a vast screen, though Pokrishevsky presented uridine as a exam case. He became meddlesome in it given 5-fluorouridine (5-FU) binds to SOD1 during a tryptophan excess essential for templated misfolding, suggesting it competence retard a acclimatisation of new SOD1 molecules (see Oct 2011 news; Dec 2012 discussion news; Wright et al., 2012). The Cashman lab found that 5-FU did indeed act in this manner. However, 5-FU is not a good healing choice for ALS given it can kill cells, pronounced Pokrishevsky. It replaces uracil in DNA and RNA, restraint DNA and RNA synthesis, and also inhibits thymidylate synthase, disrupting prolongation of thymine.

Because uridine has been used in people to negate 5-FU toxicity, Pokrishevsky tested both together. The multiple prevented SOD1-G85R-GFP aggregation. Surprisingly, so did uridine alone. Might uridine be a improved drug candidate? Unfortunately, a sip indispensable was so high as to be unreal in vivo. Cashman told Alzforum his organisation skeleton to shade some-more molecules with Pokrishevsky’s exam this year.

The exam depends on mutant SOD1 to start and say propagation, though in other presentations Pokrishevsky and Cashman explained how wild-type SOD1 competence also generate as a prion. This competence be critical given SOD1 aggregates spin adult in occasionally cases and in ALS caused by other mutations (see Oct 2010 news; Forsberg et al., 2010). The researchers wondered if variants of a ALS genes TDP-43 and FUS, or a cytoplasmic mislocalization of TDP-43 protein that outlines scarcely all tellurian ALS, competence lead to SOD1 misfolding and propagation. “Perhaps misfolded SOD1 is a common cause opposite all ALS,” Pokrishevsky told Alzforum.

If so, afterwards conditioned media from HEK cultures expressing ALS-linked versions of TDP-43 or FUS ought to enclose misfolded SOD1 that transmits a figure to uninformed dungeon cultures. Indeed, Pokrishevsky found that an antibody specific for misfolded SOD1 rescued antigen in uninformed target cells—either HEK cells or primary rodent neurons—but not if a antibody for misfolded SOD1 was initial combined to a conditioned media. Cashman resolved that once SOD1 has misfolded in one organisation of cells, it acquires a ability to broadcast a altered figure from dungeon to cell, like a prion. The lab is gearing adult to exam this suspicion in Pokrishevsky’s assembly assay, Cashman told Alzforum. Notably, TDP-43 and FUS proteins in a target cells stayed where they were; they did not have to mislocalize or total to support serve SOD1 misfolding once it had started.

Ayers called a anticipating provocative, and remarkable it fits with Cashman’s prior work joining TDP-43 pathology and SOD1 misfolding in people with occasionally ALS (Pokrishevsky et al., 2012). Cashman speculated that diagnosis with a antibody to misfolded SOD1, or a therapy that knocks down normal SOD1 expression, could delayed or hindrance ALS progression.

The Diversity of Tau
Marc Diamond of a University of Texas Southwestern Medical Center in Dallas discussed opposite strains of tau. He remarkable that notwithstanding being shaped on customarily one protein, tauopathies perceptible in innumerable ways, trimming from Alzheimer’s and frontotemporal dementias and ongoing dire encephalopathy to on-going supranuclear palsy and corticobasal degeneration. Different strains could explain both a course of tau pathology opposite a mind and a opposite phenotypes, he reasoned. 

In 2014, Diamond and colleagues reported their siege of many opposite strains of tau. Studying two, they found that one constructed large, cytoplasmic aggregates in cells and neurofibrillary tangles in mice. The other shaped small, chief inclusions both in enlightenment and a hippocampus. Importantly, as a researchers eliminated mind element from influenced to new mice, any aria confirmed a phenotype (see May 2014 news). 

In Orlando, Diamond reported his lab’s swell given afterwards with identical characterization of 18 opposite strains of tau aggregates: 8 from studious tissues, dual from tau-P301S transgenic mice, and 8 from recombinant tau fibrillized in vitro. The lab propagates them in dungeon cultures expressing tau. Since long-term countenance of full-length tau can repairs dividing cells, they use a HEK293 line expressing customarily a core partial of tau that allows aggregation, amino acids 244-372, harboring V337M and P301L mutations and fused to YFP. The scientists creatively chose this dungeon line given they suspicion it would be ideal to detect tau aggregates, Diamond told Alzforum. Disease-linked tau mutations customarily make a protein some-more receptive to prion conversion, he said, nonetheless wild-type tau can also be converted during a lower rate.

The strains had graphic identities. In dungeon culture, many were utterly stable, displaying evil aggregates such as fragile fibrils or punctate inclusions. Some total forms killed all a cells in a culture, while others killed customarily a subset. The deadliest strains were also a best during seeding new aggregates in well-bred cells, Diamond said.

To investigate a structure of a strains, a researchers borrowed a technique from a prion world, regulating a protease to digest any strain. The protease totally degraded normal tau, though a aggregating strains yielded particular patterns of fragmentation depending on that portions of their structure were stable from digestion (see Aug 2013 discussion news). These digestion patterns did not relate in any approach with toxicity or seeding ability, Diamond told Alzforum.

To learn what these tau strains competence do in a brain, a scientists injected them into a hippocampi of transgenic mice expressing tau-P301S. They saw opposite patterns of pathology. For example, one aria remained in a hippocampus while another widespread into a cortex. Some strains seeded widespread assembly of endogenous tau within 4 weeks; others took a integrate of months. The researchers beheld that a mind pathology did relate with a protease digestion patterns, in that strains with identical digestion patterns had identical in vivo distributions.

Kevin Talbot of Oxford University in a United Kingdom, who led a meeting’s module committee, praised Diamond’s work, observant a opposite strains could explain how a same protein causes different diseases.

Unlike Ayers’ SOD1 mice, Diamond’s injected mice did not get ill within a dual months a researchers have celebrated them so far, he told Alzforum. He will guard function and presence over longer time periods.

Dickie speculated that if ALS proteins do act like prions, afterwards destiny treatments could put adult a arrange of firewall to keep a problem isolated. In theory, this competence extent symptoms to one physique partial and delayed progression. Small molecules or antibodies competence retard a movement of prion-like proteins, Diamond suggested.—Amber Dance

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