Introduction:
Amyloid oligomers, the entities believed to cause toxicity in many neurodegenerative diseases, have been observed in mouse and human heart failure samples. Amyloid oligomers are a diverse group of proteins that differ in sequence, but share a common conformational structure, and may impart a shared pathogenic mechanism. The purpose of this study was to test the hypothesis that expression and accumulation of amyloid oligomers are cytotoxic and sufficient to directly cause heart failure. Polyglutamine (PQ) repeats (>50) are known to form amyloid oligomers and induce toxicity in neural cells, causing Huntington′s and other neurodegenerative diseases, while shorter PQ peptides are benign.
Hypothesis:
Cardiomyocyte-autonomous expression of an exogenous PQ amyloid oligomer will be toxic to cardiomyocytes and result in heart failure.
Methods:
Transgenic mice were created with cardiomyocyte-specific expression of an amyloid oligomer forming peptide of 83 PQ repeats (PQ83) or a non-amyloid forming peptide of 19 PQ repeats (PQ19) as a non-pathological control. Both constructs were HA tagged.
Results:
A PQ83 line with relatively low levels of expression was generated, along with a PQ19 line that expressed at approximately 9-fold the levels observed in the PQ83 line. Hearts expressing PQ83 develop cardiac dysfunction and dilation by 5 months and exhibit 100% mortality by 8 months of age, whereas PQ19 mice have normal cardiac function, morphology and lifespan. PQ83 protein accumulates in cardiomyocytes as SDS-insoluble aggresomes with amyloid oligomer-positive staining. PQ83 hearts exhibited no signs of apoptosis. Ultrastructural analysis revealed that PQ83 hearts undergo autophagy, as evidenced by increased autophagosomal and lysosomal content. PQ83 hearts also show characteristics of necrotic death, including infiltration of inflammatory cells, cardiomyocyte vacuolization and increased staining for the membrane attack complex that causes sarcolemmal permeabilization. The data confirm the hypothesis that expression of an exogenous amyloid oligomer is toxic to cardiomyocytes and is sufficient to cause heart failure. The pathogenic mechanism appears to lead to cardiomyocyte death through autophagy and necrosis.
Elucidating the Structures of Amyloid Oligomers with Macrocyclic β-Hairpin Peptides: Insights into Alzheimer’s Disease and Other Amyloid Diseases
