Destabilizing Protein Polymorphisms in the Genetic Background Direct Phenotypic Expression of Mutant SOD1 Toxicity

Abstract

Genetic background exerts a strong modulatory effect on the toxicity of aggregation-prone proteins in conformational diseases. In addition to influencing the misfolding and aggregation behavior of the mutant proteins, polymorphisms in putative modifier genes may affect the molecular processes leading to the disease phenotype. Mutations in SOD1 in a subset of familial amyotrophic lateral sclerosis (ALS) cases confer dominant but clinically variable toxicity, thought to be mediated by misfolding and aggregation of mutant SOD1 protein. While the mechanism of toxicity remains unknown, both the nature of the SOD1 mutation and the genetic background in which it is expressed appear important. To address this, we established a Caenorhabditis elegans model to systematically examine the aggregation behavior and genetic interactions of mutant forms of SOD1. Expression of three structurally distinct SOD1 mutants in C. elegans muscle cells resulted in the appearance of heterogeneous populations of aggregates and was associated with only mild cellular dysfunction. However, introduction of destabilizing temperature-sensitive mutations into the genetic background strongly enhanced the toxicity of SOD1 mutants, resulting in exposure of several deleterious phenotypes at permissive conditions in a manner dependent on the specific SOD1 mutation. The nature of the observed phenotype was dependent on the temperature-sensitive mutation present, while its penetrance reflected the specific combination of temperature-sensitive and SOD1 mutations. Thus, the specific toxic phenotypes of conformational disease may not be simply due to misfolding/aggregation toxicity of the causative mutant proteins, but may be defined by their genetic interactions with cellular pathways harboring mildly destabilizing missense alleles.

A natural product inhibits the initiation of α-synuclein aggregation and suppresses its toxicity

“…Motility in C. elegans declines during aging and it can be measured in liquid media by counting the number of body bends per unit of time (37). This phenotypic readout has been used extensively for identification of genes and pathways connected to age-related protein homeostasis, as well as for the definition of modifiers of protein aggregation (25, 35, 36); both of these processes are closely associated with the onset and development of neurodegenerative diseases (5,7,38).…”

Spinal motor neuron protein supersaturation patterns are associated with inclusion body formation in ALS

“…Disease-associated mutations decrease the solubility of SOD1, resulting in higher supersaturation levels than is the case for the wild-type protein. In addition, it is well established that misfolding of one protein can disrupt protein homeostasis and lead to the aggregation of other metastable proteins (75). Hence, the misfolding and aggregation of SOD1 are likely to lead to the destabilization and recruitment of other proteins into inclusions, either through direct interactions or indirectly through the disruption of the protein homeostasis system and aggregation of other supersaturated proteins (57).…”

A Novel Interaction Between Aging and ER Overload in a Protein Conformational Dementia

“…Tissue from mice or worms was lysed with either SDS sample buffer, SDS containing and SDS-free RIPA, or worm lysis buffer (Gidalevitz et al 2009). Western blotting was performed under denaturing and nondenaturing (Miranda et al 2004) conditions using antibodies against GFP (Clonetch), a-tubulin (Sigma-Aldrich), ATF6 (Imgenex), eIF2a/eIF2aP (Cell Signaling), neuroserpin (Miranda et al 2008), LC3-I/-II (Thelen et al 2012), and actin (Sigma-Aldrich).…”

“…These movement defects can be reduced by RNAi-mediated depletion of the YFP fusion protein, thus SRP-2 H302R aggregation seems to affect muscle function ( Figure 3F). As a control for the experiments we use the established lines for YFP and Q40::YFP as previously described (Gidalevitz et al 2009). …”