Cytotoxic Aggregation and Amyloid Formation by the Myostatin Precursor Protein

Abstract

Myostatin, a negative regulator of muscle growth, has been implicated in sporadic inclusion body myositis (sIBM). sIBM is the most common age-related muscle-wastage disease with a pathogenesis similar to that of amyloid disorders such as Alzheimer's and Parkinson's diseases. Myostatin precursor protein (MstnPP) has been shown to associate with large molecular weight filamentous inclusions containing the Alzheimer's amyloid beta peptide in sIBM tissue, and MstnPP is upregulated following ER stress. The mechanism for how MstnPP contributes to disease pathogenesis is unknown. Here, we show for the first time that MstnPP is capable of forming amyloid fibrils in vitro. When MstnPP-containing Escherichia coli inclusion bodies are refolded and purified, a proportion of MstnPP spontaneously misfolds into amyloid-like aggregates as characterised by electron microscopy and binding of the amyloid-specific dye thioflavin T. When subjected to a slightly acidic pH and elevated temperature, the aggregates form straight and unbranched amyloid fibrils 15 nm in diameter and also exhibit higher order amyloid structures. Circular dichroism spectroscopy reveals that the amyloid fibrils are dominated by β-sheet and that their formation occurs via a conformational change that occurs at a physiologically relevant temperature. Importantly, MstnPP aggregates and protofibrils have a negative effect on the viability of myoblasts. These novel results show that the myostatin precursor protein is capable of forming amyloid structures in vitro with implications for a role in sIBM pathogenesis.

Natural tri- to hexapeptides self-assemble in water to amyloid β-type fiber aggregates by unexpected α-helical intermediate structures

“…2 A and B). Our CD spectra pointed to a combination of α-helix and poly-L-proline-like II conformations previously observed in amyloidogenic peptides prior to assembly (12). The α-helical content increased when the critical gel forming concentration was exceeded.…”

Amyloid β-Sheet Secondary Structure Identified in UV-Induced Cataracts of Porcine Lenses using 2D IR Spectroscopy

“…The 2D IR spectra exhibit the 1621 cm −1 peak and the corresponding cross peaks of amyloid β-sheets. Short amyloid morphologies are not uncommon and are observed in TEM images of other proteins with fibrillary, 41; 42 prefibrillar, 43; 44 oligomeric, 45 or amorphous morphologies. 46 These images and spectra are shown to illustrate the diversity in length that crystallin amyloids can adopt, as measured by TEM, and that 2D IR spectra exhibit characteristic amyloid β-sheet secondary structure even for lengths that are difficult to resolve with TEM.…”

Sporadic inclusion-body myositis: Conformational multifactorial ageing-related degenerative muscle disease associated with proteasomal and lysosomal inhibition, endoplasmic reticulum stress, and accumulation of amyloid-β42 oligomers and phosphorylated tau

“…Possibly, AbPP binding to MSTNPP causes its posttranslational modification that lessens its traffic and degradation, resulting in accumulation. Recently, the importance of MSTNPP accumulation in s-IBM was emphasized by the studies of others [122] demonstraing that MSTNPP is capable of forming intracellular b-pleated sheet amyloid. Since MSTN physically associates with AbPP/Ab [120,121], it is possible, as we have previously proposed [120], that these two proteins might enhance each other's aggregation, oligomerization and b-pleated sheet formation.…”