Relationship between amyloid deposition and intracellular structural changes in familial amyloidotic polyneuropathy

Early transverse tubule involvement in cardiomyocytes in hereditary transthyretin amyloidosis; A possible cause of cardiac events

BACKGROUND

Cardiac involvement is one of the most frequent and fatal manifestations of hereditary transthyretin (ATTRv) amyloidosis. This study sought to clarify the pathogenesis of ATTRv amyloidosis, specifically, how transthyretin (TTR) amyloid begins to deposit in cardiomyocytes and how this deposition progresses in these cells.

METHODS

We analyzed autopsy cardiac tissues from five patients with ATTRv amyloidosis by using confocal microscopy with thioflavin S staining and immunofluorescence and electron microscopy to demonstrate the pattern of TTR amyloid deposition in cardiomyocytes.

RESULTS

We demonstrated predominant amyloid deposition in the transverse tubules (t-tubules) of cardiomyocytes at the early stage of TTR amyloid deposition. Also, a pattern of the progression of amyloid deposition from deeply invaginated extracellular matrix, i.e. t-tubules, to cell surface extracellular matrix, i.e. basement membrane, was noted. Three-dimensional confocal microscopic images revealed the abnormal architecture of the t-tubules with nodular swelling, branching, and confluence in the cardiomyocytes with amyloid deposition. Double immunofluorescence staining with anti-TTR antibody and CACNA1C antibody demonstrated reduced voltage-dependent calcium channels around amyloid deposition.

CONCLUSIONS

Our pathological study demonstrated that t-tubule involvement is an early event in cardiomyocytes in the pathogenesis of ATTRv amyloidosis. This finding may indicate that disruption of t-tubules in cardiomyocytes may contribute to the pathogenesis of cardiac events including heart failure and arrhythmia.

Biochemical and Electrophysiological Modification of Amyloid Transthyretin on Cardiomyocytes

Transthyretin (TTR) amyloidoses are familial or sporadic degenerative conditions that often feature heavy cardiac involvement. Presently, no effective pharmacological therapy for TTR amyloidoses is available, mostly due to a substantial lack of knowledge about both the molecular mechanisms of TTR aggregation in tissue and the ensuing functional and viability modifications that occur in aggregate-exposed cells. TTR amyloidoses are of particular interest regarding the relation between functional and viability impairment in aggregate-exposed excitable cells such as peripheral neurons and cardiomyocytes. In particular, the latter cells provide an opportunity to investigate in parallel the electrophysiological and biochemical modifications that take place when the cells are exposed for various lengths of time to variously aggregated wild-type TTR, a condition that characterizes senile systemic amyloidosis. In this study, we investigated biochemical and electrophysiological modifications in cardiomyocytes exposed to amyloid oligomers or fibrils of wild-type TTR or to its T4-stabilized form, which resists tetramer disassembly, misfolding, and aggregation. Amyloid TTR cytotoxicity results in mitochondrial potential modification, oxidative stress, deregulation of cytoplasmic Ca²⁺ levels, and Ca²⁺ cycling. The altered intracellular Ca²⁺ cycling causes a prolongation of the action potential, as determined by whole-cell recordings of action potentials on isolated mouse ventricular myocytes, which may contribute to the development of cellular arrhythmias and conduction alterations often seen in patients with TTR amyloidosis. Our data add information about the biochemical, functional, and viability alterations that occur in cardiomyocytes exposed to aggregated TTR, and provide clues as to the molecular and physiological basis of heart dysfunction in sporadic senile systemic amyloidosis and familial amyloid cardiomyopathy forms of TTR amyloidoses.

Endoscopic Findings of Small-Bowel Lesions in Familial Amyloid Polyneuropathy: A Case Report

Familial amyloid polyneuropathy (FAP) is an autosomal dominant disease associated with the mutations in the transthyretin gene. To date, the endoscopic findings of the small-bowel lesions of FAP have never been described. We report a rare case of FAP with gastrointestinal involvement. A 71-year-old woman complaining of refractory diarrhea for 1 year was referred to our institution. She had sensory disturbance, movement disorder due to muscle weakness, and autonomic nervous system disorders including orthostatic hypotension and dysuria. Her eldest sister had cardiac amyloidosis. Small-bowel radiography and retrograde double-balloon endoscopy (DBE) revealed that fine granular protrusions were diffusely observed both in the jejunum and ileum. Histologic examination of the biopsy specimens obtained from the small bowel revealed perivascular amyloid deposits mainly in the muscularis mucosae and submucosa, which were immunoreactive with transthyretin antibodies. Analysis of the genomic DNA showed a heterozygous Gly47Val mutation in the transthyretin gene. Thus a diagnosis of FAP was established. Diffuse fine granular protrusions in the jejunum and the ileum visualized by small-bowel radiography and DBE may be characteristic of FAP. Multiple biopsies from the gastrointestinal mucosa are recommended for the definitive histologic diagnosis of FAP.

Facing the challenges of ventricular hypertrophy: the eyes don't lie

We describe the case of a 47-year-old man with new-onset heart failure who was found to have severe biventricular wall thickening. We present comprehensive data from invasive and non-invasive multimodality imaging, genetic and histologic tests, and briefly describe their importance in the final diagnosis. To our knowledge, this is the first case of the Portuguese variant of familial amyloid polyneuropathy presenting with heart failure in the fifth decade of life. This is an unusual case report, but also an illustration of how to approach any patient with suspected infiltrative cardiomyopathy.

Familial amyloidotic polyneuropathy and transthyretin

There has been much progress in our understanding of transthyretin (TTR)-related amyloidosis including familial amyloidotic polyneuropathy (FAP), senile systemic amyloidosis and its related disorders from many clinical and experimental aspects. FAP is an inherited severe systemic amyloidosis caused by mutated TTR, and characterized by amyloid deposition mainly in the peripheral nervous system and the heart. Liver transplantation is the only available treatment for the disease. FAP is now recognized not to be a rare disease, and to have many variations based on genetical and biochemical variations of TTR. This chapter covers the recent advances in the clinical and pathological aspects of, and therapeutic approaches to FAP, and the trend as to the molecular pathogenesis of TTR.