Cellular consequences of transthyretin deposition

Genotype-phenotype correlation and course of transthyretin familial amyloid polyneuropathies in France

OBJECTIVE

To compare the natural history of familial transthyretin amyloid polyneuropathies (FAP) due to the Val30Met, Ser77Tyr, and Ile107Val mutations in France with the classical Portuguese Val30Met FAP.

METHODS

We compared 84 French patients with a control group of 110 Portuguese patients carrying the Val30Met mutation also living in France, all referred to and followed at the French National FAP Reference Center from 1988 to 2010. Clinical examination, functional and walking disability scores, nerve conduction studies, and muscle biopsies are reported. We also conducted a comprehensive literature review to further determine the range of phenotypic expression.

RESULTS

By comparison with Portuguese Val30Met FAP, French Ile107Val, Ser77Tyr, and LateVal30Met FAP showed more rapid and severe disease progression; onset of gait disorders was 3 times more rapid (p < 0.0001) and the rate of modified Norris test decline was up to 40 times faster in Ile107Val patients (p < 0.0001). Median survival was much shorter in Ile107Val and in Val30Met mutation with late onset (>50 years; LateMet30) FAP (p = 0.0005). Other distinctive features relative to the Portuguese patients included atypical clinical presentations, demyelination on nerve conduction studies (p = 0.0005), and difficult identification of amyloid deposits in nerve and muscle biopsies.

INTERPRETATION

Ile107Val and LateMet30 mutations are associated with the most debilitating and severe FAP ever described, with rapid onset of tetraparesis and shorter median survival. It could be explained by frequent large-fiber involvement and associated demyelination and more severe axonal loss. These findings have major implications for genetic counseling and patient management as new therapeutic options are being assessed in clinical trials (TTR gene silencing).

Human placental transthyretin in fetal growth restriction in combination with preeclampsia and the HELLP syndrome

Fetal growth restriction is a serious, still poorly understood pregnancy-related pathology often associated with preeclampsia. Recent studies speculate on the role of human transthyretin, a carrier protein for thyroxin and retinol binding protein, in the etiology of both pregnancy pathologies. Objective was to investigate the localization and abundance of transthyretin (TTR) in placentas of pregnancies suffering from fetal growth restriction with and without preeclampsia and HELLP. This was a retrospective case control study on human paraffin-embedded placentas from pregnancies with a gestational age at delivery between the 24th and 34th week of gestation. 16 placentas were included in this study, 11 cases and 5 from normotensive pregnancies as controls. Cases were divided into three groups: four from early onset idiopathic intrauterine growth restriction (IUGR), four from early-onset severe preeclampsia (PE), and three from early-onset IUGR with preeclampsia plus HELLP syndrome. Distribution and abundance of TTR were investigated by means of immunohistochemistry. Semi quantitative analysis of TTR staining of placental sections revealed that TTR was mostly expressed in the villous trophoblast covering placental villi. Only weak staining of TTR in villous stroma could be detected. The comparison of placentas revealed that in pure IUGR and severe PE there is a much stronger TTR reactivity compared to controls and cases with IUGR + PE + HELLP. Concluding, the study showed that TTR is dysregulated in cases of IUGR and severe early onset preeclampsia. Interestingly, TTR expression is not affected in cases with HELLP syndrome that reveal the same staining intensities as age-matched controls.

Amyloidogenic and associated proteins in systemic amyloidosis proteome of adipose tissue

In systemic amyloidoses, widespread deposition of protein as amyloid causes severe organ dysfunction. It is necessary to discriminate among the different forms of amyloid to design an appropriate therapeutic strategy. We developed a proteomics methodology utilizing two-dimensional polyacrylamide gel electrophoresis followed by matrix-assisted laser desorption/ionization mass spectrometry and peptide mass fingerprinting to directly characterize amyloid deposits in abdominal subcutaneous fat obtained by fine needle aspiration from patients diagnosed as having amyloidoses typed as immunoglobulin light chain or transthyretin. Striking differences in the two-dimensional gel proteomes of adipose tissue were observed between controls and patients and between the two types of patients with distinct, additional spots present in the patient specimens that could be assigned as the amyloidogenic proteins in full-length and truncated forms. In patients heterozygotic for transthyretin mutations, wild-type peptides and peptides containing amyloidogenic transthyretin variants were isolated in roughly equal amounts from the same protein spots, indicative of incorporation of both species into the deposits. Furthermore novel spots unrelated to the amyloidogenic proteins appeared in patient samples; some of these were identified as isoforms of serum amyloid P and apolipoprotein E, proteins that have been described previously to be associated with amyloid deposits. Finally changes in the normal expression pattern of resident adipose proteins, such as down-regulation of alphaB-crystallin, peroxiredoxin 6, and aldo-keto reductase I, were observed in apparent association with the presence of amyloid, although their levels did not strictly correlate with the grade of amyloid deposition. This proteomics approach not only provides a way to detect and unambiguously type the deposits in abdominal subcutaneous fat aspirates from patients with amyloidoses but it may also have the capability to generate new insights into the mechanism of the diseases by identifying novel proteins or protein post-translational modifications associated with amyloid infiltration.

Stabilization of partially folded states in protein folding/misfolding transitions by hydrostatic pressure

In the last few years, hydrostatic pressure has been extensively used in the study of both protein folding and misfolding/aggregation. Compared to other chemical or physical denaturing agents, a unique feature of pressure is its ability to induce subtle changes in protein conformation, which allow the stabilization of partially folded intermediate states that are usually not significantly populated under more drastic conditions (e.g., in the presence of chemical denaturants or at high temperatures). Much of the recent research in the field of protein folding has focused on the characterization of folding intermediates since these species appear to be involved in a variety of disease-causing protein misfolding and aggregation events. The exact mechanisms of these biological phenomena, however, are still poorly understood. Here, we review recent examples of the use of hydrostatic pressure as a tool to obtain insight into the forces and energetics governing the productive folding or the misfolding and aggregation of proteins.