Clinical and Molecular Phenotypes of Low-Penetrance Variants of NLRP3: Diagnostic and Therapeutic Challenges

OBJECTIVE

Cryopyrin-associated periodic syndromes (CAPS) result from gain-of-function mutations in the NLRP3 gene, which causes excessive release of interleukin-1β (IL-1β) and systemic inflammation. While pathogenetic NLRP3 variant phenotypes are well-characterized, low-penetrance NLRP3 variants represent a significant clinical challenge. The aims of this study were to determine the clinical phenotype, the in vitro biologic phenotype, and the effect of anti-IL-1 treatment in patients with low-penetrance NLRP3 variants.

METHODS

A multicenter study of consecutive symptomatic patients with low-penetrance NLRP3 variants recruited from 7 centers between May 2012 and May 2013 was performed. The observed findings were transferred into a study database, from which they were extracted for analysis. Controls were patients with a known pathogenetic NLRP3 variant. Clinical presentation and CAPS markers of inflammation were captured. Functional assays of inflammasome activation, including caspase 1 activity, NF-κB release, cell death, and IL-1β release, were performed. Treatment effects of IL-1 were determined. Comparisons between low-penetrance and pathogenetic NLRP3 variants were performed.

RESULTS

The study included 45 patients, 21 of which were female (47%); 26 of the patients (58%) were children. NLRP3 low-penetrance variants identified in the patients were Q703K (n = 19), R488K (n = 6), and V198M (n = 20). In the controls, 28 had pathogenetic NLRP3 variants. Patients with low-penetrance NLRP3 variants had significantly more fever (76%) and gastrointestinal symptoms (73%); eye disease, hearing loss, and renal involvement were less common. Functional inflammasome testing identified an intermediate phenotype in low-penetrance NLRP3 variants as compared to wild-type and pathogenetic NLRP3 variants. All treated patients responded to IL-1 inhibition, with complete response documented in 50% of patients.

CONCLUSION

Patients with low-penetrance NLRP3 variants display a distinct clinical phenotype and an intermediate biologic phenotype, including IL-1β and non-IL-1β-mediated inflammatory pathway activation.

Proteomics of rimmed vacuoles define new risk allele in inclusion body myositis

OBJECTIVE

Sporadic inclusion body myositis (sIBM) pathogenesis is unknown; however, rimmed vacuoles (RVs) are a constant feature. We propose to identify proteins that accumulate within RVs.

METHODS

RVs and intact myofibers were laser microdissected from skeletal muscle of 18 sIBM patients and analyzed by a sensitive mass spectrometry approach using label-free spectral count-based relative protein quantification. Whole exome sequencing was performed on 62 sIBM patients. Immunofluorescence was performed on patient and mouse skeletal muscle.

RESULTS

A total of 213 proteins were enriched by >1.5 -fold in RVs compared to controls and included proteins previously reported to accumulate in sIBM tissue or when mutated cause myopathies with RVs. Proteins associated with protein folding and autophagy were the largest group represented. One autophagic adaptor protein not previously identified in sIBM was FYCO1. Rare missense coding FYCO1 variants were present in 11.3% of sIBM patients compared with 2.6% of controls (p = 0.003). FYCO1 colocalized at RVs with autophagic proteins such as MAP1LC3 and SQSTM1 in sIBM and other RV myopathies. One FYCO1 variant protein had reduced colocalization with MAP1LC3 when expressed in mouse muscle.

INTERPRETATION

This study used an unbiased proteomic approach to identify RV proteins in sIBM that included a novel protein involved in sIBM pathogenesis. FYCO1 accumulates at RVs, and rare missense variants in FYCO1 are overrepresented in sIBM patients. These FYCO1 variants may impair autophagic function, leading to RV formation in sIBM patient muscle. FYCO1 functionally connects autophagic and endocytic pathways, supporting the hypothesis that impaired endolysosomal degradation underlies the pathogenesis of sIBM. Ann Neurol 2017;81:227-239.

The Transcriptional Regulation of FOXO Genes in Thyrocytes

FOXO transcription factors are key regulators of DNA damage repair, proliferation and apoptosis in thyrocytes. Thyroid malignancies show impaired FOXO function. In this study, we investigated the transcriptional regulation of FOXO isoforms in thyroid epithelial cells. mRNA expression of FOXO isoforms (FOXO1, 3 and 4) was determined in FRTL-5 cells stimulated with different growth factors and H2O2. Furthermore, the impact of PI3K/AKT signalling on FOXO transcription was investigated in PI3K p110α mutant FRTL-5 cells and regulatory dependence of FOXO transcription on FOXO was studied in FRTL-5 cells with hFOXO3 overexpression. Finally, mRNA expression levels of FOXO isoforms were determined in human epithelial thyroid tumours. Growth factor deprivation induced transcription of FOXO1, 3 and 4, whereas insulin stimulation decreased FOXO1 and FOXO4 transcription in FRTL-5 cells. Inhibition of the PI3K/AKT cascade amplified FOXO1 and FOXO4 expression. In contrast, H2O2 and TSH did not influence FOXO transcription in thyrocytes. Overexpression of PI3K p110α inhibited FOXO3 and induced FOXO4 transcription. In human thyroid tumours, FOXO1 and FOXO3 mRNA levels were significantly downregulated in papillary thyroid carcinoma when compared to normal tissues. In contrast, follicular thyroid carcinomas showed significant upregulation of FOXO4 mRNA.In this paper, we demonstrate an influence of PI3K signalling on FOXO transcription in thyrocytes. Moreover, we show that thyroid cancers exhibit alterations in FOXO transcription besides the previously reported alterations in posttranslational FOXO3 regulation. These findings may add to the concept of targeting the PI3K pathway in advanced thyroid cancers.

Interaction of thyroid hormone with brown adipose tissue

Brown adipose tissue (BAT) plays an important role in regulating core-body temperature in various species including man. [18F]FDGPET/ CT imaging first revealed the presence of metabolically active BAT depots and that decreased BAT function is associated with various metabolic conditions. Thyroid hormone (TH) in concert with sympathetic nervous system signalling (SNS) stimulates BAT thermogenesis and thyroid disorders result in dysfunctional BAT. Currently, research is focussing not only on BAT regulation but also on browning of white adipose tissue (WAT) to BAT beige adipose tissue (BeAT) in order to develop novel treatments for human obesity and related conditions. While [18F]FDG-PET/ CT imaging is continuing to provide valuable insights into BAT and BeAT function in health and disease, there is a pressing need to develop alternative radiotracers that reliably track their activity in vivo. As a result it is expected that preclinical micro PET/CT investigations of BAT and BeAT will gain in prominence.

The aim of this short review is to i) describe fundamentals in BAT biology, ii) highlight some of the clinical and preclinical studies performed on humans and rodents with a focus on TH, BAT and PET/CT, and iii) bridge these data with our own studies within the DFG thyroid transact priority program.

Interaction of thyroid hormone with brown adipose tissue. Lessons learned from PET-CT

Brown adipose tissue (BAT) plays an important role in regulating core-body temperature in various species including man. [18F]FDG-PET/CT imaging first revealed the presence of metabolically active BAT depots and that decreased BAT function is associated with various metabolic conditions. Thyroid hormone (TH) in concert with sympathetic nervous system signalling (SNS) stimulates BAT thermogenesis and thyroid disorders result in dysfunctional BAT. Currently, research is focussing not only on BAT regulation but also on browning of white adipose tissue (WAT) to BAT beige adipose tissue (BeAT) in order to develop novel treatments for human obesity and related conditions. While [18F]FDG-PET/CT imaging is continuing to provide valuable insights into BAT and BeAT function in health and disease, there is a pressing need to develop alternative radiotracers that reliably track their activity in vivo. As a result it is expected that preclinical micro PET/CT investigations of BAT and BeAT will gain in prominence. The aim of this short review is to i) describe fundamentals in BAT biology, ii) highlight some of the clinical and preclinical studies performed on humans and rodents with a focus on TH, BAT and PET/CT, and iii) bridge these data with our own studies within the DFG thyroid transact priority program.

An improved Peltier effect-based instrument for critical temperature threshold measurement in cold- and heat-induced urticaria

BACKGROUND

Cold- and heat-induced urticaria are chronic physical urticaria conditions in which wheals, angioedema or both are evoked by skin exposure to cold and heat respectively. The diagnostic work up of both conditions should include skin provocation tests and accurate determination of critical temperature thresholds (CTT) for producing symptoms in order to be able to predict the potential risk that each individual patient faces and how this may be ameliorated by therapy.

OBJECTIVE

To develop and validate TempTest(®) 4, a simple and relatively inexpensive instrument for the accurate determination of CTT which may be used in clinical practice.

METHODS

TempTest(®) 4 has a single 2 mm wide 350 mm U-shaped Peltier element generating a temperature gradient from 4 °C to 44 °C along its length. Using a clear plastic guide placed over the skin after provocation, CTT values may be determined with an accuracy of ±1 °C. Here, TempTest(®) 4 was compared with its much more expensive predecessor, TempTest(®) 3, in inducing wheals in 30 cold urticaria patients.

RESULTS

Both TempTest(®) 4 and TempTest(®) 3 induced wheals in all 30 patients between 8 ° and 28 °C. There was a highly significant (P < 0.0001) correlation between the instruments in the CTT values in individual patients.

CONCLUSION

The TempTest(®) 4 is a simple, easy to use, licensed, commercially available and affordable instrument for the determination of CTTs in both cold- and heat-induced urticaria.