A low amyloidogenic E61K transthyretin mutation may cause familial amyloid polyneuropathy

Abstract

Patients with transthyretin (TTR)‐type familial amyloid polyneuropathy (FAP) typically exhibit sensory dominant polyneuropathy and autonomic neuropathy. However, the molecular pathogenesis of the neuropathy remains unclear. In this study, we characterize the features of FAP TTR the substitution of lysine for glutamic acid at position 61 (E61K). This FAP was late‐onset, with sensory dominant polyneuropathy, autonomic neuropathy, and cardiac amyloidosis. Interestingly, no amyloid deposits were found in the endoneurium of the four nerve specimens examined. Therefore, we examined the amyloidogenic properties of E61K TTR in vitro. Recombinant wild‐type TTR, the substitution of methionine for valine at position 30 (V30M) TTR, and E61K TTR proteins were incubated at 37°C for 72 hr, and amyloid fibril formation was assessed using the thioflavin‐T binding assay. Amyloid fibril formation by E61K TTR was less than that by V30M TTR, and similar to that by wild‐type TTR. E61K TTR did not have an inhibitory effect on neurite outgrowth from adult rat dorsal root ganglion (DRG) neurons, but V30M TTR did. Furthermore, we studied the sural nerve of our patient by terminal deoxynucleotidyl transferase dUTP nick end labeling and electron microscopy. A number of apoptotic cells were observed in the endoneurium of the nerve by transferase dUTP nick end labeling. Chromatin condensation was confirmed in the nucleus of non‐myelinating Schwann cells by electron microscopy. These findings suggest that E61K TTR is low amyloidogenic, in vitro and in vivo. However, TTR aggregates and amyloid fibrils in the DRG may cause sensory impairments in FAP because the DRG has no blood–nerve barrier. Moreover, Schwann cell apoptosis may contribute to the neurodegeneration.

Variant and wild type transthyretin amyloidosis: two sides of the same coin or different currencies in different pockets?

“…There is no doubt that the clinical development of heart failure in ATTR cardiomyopathy of either form is due to massive myocardial amyloid infiltration, but neuronal amyloid infiltration is probably not the major underlying pathophysiologic mechanism for early symptomatic ATTRv neuropathy. This is supported by prior studies which have shown that amyloid fibres are not always found in nerves in the early stages of amyloid neuropathy, 5 and rare variants may have neuropathy in the apparent absence of nerve infiltration 6 . The exact mode of neuronal damage in neuropathic ATTRv is not fully elucidated, but it is well‐established that pre‐amyloid oligomers are neurotoxic in vitro , 7 and there is a reasonable consensus that neurotoxicity plays a significant role in patients with the disease 8 .…”

Analysis of amyloidogenic transthyretin mutations using continuum solvent free energy calculations

“…Interestingly, for most known amyloidogenic mutations (V30G, 38 D38A, 12 E54G, 15,43 E54K, 43 L55P, 44 L58H, 46 T60A, 16 E61K, 48 S77Y, 49 Y78F, 50 I84A, 51 I84S, 40 H88S, 52 H88R, 52 Y114C, 54 and Y114H 25 ) our results indicate a significant overall destabilizing effect on the tetramer. Note, that at this analysis stage influences on monomer stability, dimer formation and energetics of dimer association to tetramers are all included (decomposition see next paragraph).…”

“…Indeed, crystal structures of TTR mutations indicate only small conformational changes in the globular form compared to wild type 5,30,31 . The approach was applied to 36 TTR mutations for which either an increased (A25T, 37 V30G, 38 V30M, 5,39,40 D38A, 12 S52P, 41,42 E54G, 15,43 E54K, 43 L55P, 44,45 L58H, 46 T60A, 16,47 E61K, 48 S77Y, 49 Y78F, 50 I84A, 51 I84S, 40 H88S, 52 H88R, 52 E89K, 53 Y114C, 54–57 Y114H, 25 V122I 58 ) or decreased (S85P, 3 H88A, 52 H88F, 52 H88Y, 52 E92P, 40 V94P, 3 R104H, 5 A108I, 59 A108V, 59 A108W, 59 A109V, 59 A109T, 60 T119M, 61 T119W, 3 and T119Y 3 ) tendency for amyloidosis has been reported experimentally. Since experimentally only a tendency for amyloidosis is known it allowed us only a qualitative comparison with calculated stability changes.…”

Physiological Metals Can Induce Conformational Changes in Transthyretin Structure: Neuroprotection or Misfolding Induction?

“…The superposition of the two structures reveals that there is a common Ca 2+ site between Glu66 and Asp99 of monomer A, while a second site is detected around N-terminus portions in the crystal at higher Ca 2+ concentrations, Figure 5a,b. Different variants of TTR have been solved alone or in complex with ligands, in the presence of Ca 2+ , and in these cases no relevant structural differences were detected [59,61,62].…”