UC Santa Barbara

Protein misfolding has been implicated in a number of neurodegenerative diseases, including Alzheimer’s Disease (AD), Parkinson’s Disease, and amyotrophic lateral sclerosis (ALS). In these diseases, one or more proteins adopt a non-native conformation that is prone to aggregate into small soluble oligomers and larger fibrils, which typically present as abnormal protein deposits in the afflicted cells or tissues. Understanding the aggregation of these proteins is essential to the development of effective disease-modifying therapeutics. TAR DNA binding protein of 43 kDa (TDP-43) is one such protein that is believed to play a causative role in sporadic ALS and tau- and alpha synuclein-negative frontotemporal lobar degeneration (FTLD-TDP), and is also observable in a significant percentage of individuals with AD, where it is associated with increased cognitive decline. Atomic force microscopy (AFM) was used as a complementary technique to ion mobility-mass spectrometry (IM-MS) to elucidate the early-stage aggregation of the amyloidogenic core region of TDP-43, TDP-43(307-319). TDP-43(307-319) aggregation was shown to progress via a bifurcated pathway, with toxic oligomers off pathway from fibrillization. Two ALS-related mutations of TDP-43 increase aggregation while a synthetic non-toxic mutant prevents oligomerization but does not suppress fibrilization. Similar experiments with a fragment of the familial ALS-related protein superoxide dismutase-1, SOD1(28-38), show that the formation of ordered, non-fibrillar aggregates was tied to the presence of a potentially toxic corkscrew oligomer. TDP-43(307-319) aggregation was also modulated using two methods. First, computationally generated inhibitors molecules developed using the Join Pharmacophore Space (JPS) were shown to disrupt oligomers believed to play a toxic role in ALS but were not observed to impact off-pathway fibrillization. Further refinement of the JPS algorithm will be required if fibril disruption is shown to be necessary for effective treatment of ALS. Next, TDP-43(307-319) was co-aggregated with a fragment of the AD-implicated protein amyloid beta, Aβ(25-35). Coaggregation of TDP-43(307-319) and Aβ(25-35) results in increased formation of toxic oligomers for both peptides. Coaggregation was also conducted with a mutation of TDP-43(307-319) that suppresses toxic oligomers, and potentially toxic Aβ(25-35) oligomers were observed to increase fibrilization of TDP-43. These results indicate that cross talk between amyloidogenic proteins must be considered in the development of therapeutics for related diseases.