Pharmacological potentiators of the calcium signaling cascade identified by high-throughput screening

Esc peptides and derivatives potentiate the activity of CFTR with gating defects and display antipseudomonal activity in cystic fibrosis-like lung disease

Cystic fibrosis (CF) is a rare disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), a chloride channel with an important role in the airways. Despite the clinical efficacy of present modulators in restoring the activity of defective CFTR, there are patients who show persistent pulmonary infections, mainly due to Pseudomonas aeruginosa. Recently, we reported an unprecedented property of antimicrobial peptides i.e. Esc peptides, which consists in their ability to act as potentiators of CFTR carrying the most common mutation (the loss of phenylalanine 508) affecting protein folding, trafficking and gating. In this work, by electrophysiology experiments and computational studies, the capability of these peptides and de-novo designed analogs was demonstrated to recover the function of other mutated forms of CFTR which severely affect the channel gating (G551D and G1349D). This is presumably due to direct interaction of the peptides with the nucleotide binding domains (NBDs) of CFTR, followed by a novel local phenomenon consisting in distancing residues located at the cytosolic side of the NBDs interface, thus stabilizing the open conformation of the pore at its cytosolic end. The most promising peptides for the dual antimicrobial and CFTR potentiator activities were also shown to display antipseudomonal activity in conditions mimicking the CF pulmonary ion transport and mucus obstruction, with a higher efficacy than the clinically used colistin. These studies should assist in development of novel drugs for lung pathology in CF, with dual CFTR potentiator and large spectrum antibiotic activities.

Anoctamin pharmacology

TMEM16 proteins, also known as anoctamins, are a family of ten membrane proteins with various tissue expression and subcellular localization. TMEM16A (anoctamin 1) is a plasma membrane protein that acts as a calcium-activated chloride channel. It is expressed in many types of epithelial cells, smooth muscle cells and some neurons. In airway epithelial cells, TMEM16A expression is particularly enhanced by inflammatory stimuli that also promote goblet cell metaplasia and mucus hypersecretion. Therefore, pharmacological modulation of TMEM16A could be beneficial to improve mucociliary clearance in chronic obstructive respiratory diseases. However, the correct approach to modulate TMEM16A activity (activation or inhibition) is still debated. Pharmacological inhibitors of TMEM16A could also be useful as anti-hypertensive agents given the TMEM16A role in smooth muscle contraction. In contrast to TMEM16A, TMEM16F (anoctamin 6) behaves as a calcium-activated phospholipid scramblase, responsible for the externalization of phosphatidylserine on cell surface. Inhibitors of TMEM16F could be useful as anti-coagulants and anti-viral agents. The role of other anoctamins as therapeutic targets is still unclear since their physiological role is still to be defined.

Detailed Analysis of ITPR1 Missense Variants Guides Diagnostics and Therapeutic Design

BACKGROUND

The ITPR1 gene encodes the inositol 1,4,5-trisphosphate (IP3 ) receptor type 1 (IP3 R1), a critical player in cerebellar intracellular calcium signaling. Pathogenic missense variants in ITPR1 cause congenital spinocerebellar ataxia type 29 (SCA29), Gillespie syndrome (GLSP), and severe pontine/cerebellar hypoplasia. The pathophysiological basis of the different phenotypes is poorly understood.

OBJECTIVES

We aimed to identify novel SCA29 and GLSP cases to define core phenotypes, describe the spectrum of missense variation across ITPR1, standardize the ITPR1 variant nomenclature, and investigate disease progression in relation to cerebellar atrophy.

METHODS

Cases were identified using next-generation sequencing through the Deciphering Developmental Disorders study, the 100,000 Genomes project, and clinical collaborations. ITPR1 alternative splicing in the human cerebellum was investigated by quantitative polymerase chain reaction.

RESULTS

We report the largest, multinational case series of 46 patients with 28 unique ITPR1 missense variants. Variants clustered in functional domains of the protein, especially in the N-terminal IP3 -binding domain, the carbonic anhydrase 8 (CA8)-binding region, and the C-terminal transmembrane channel domain. Variants outside these domains were of questionable clinical significance. Standardized transcript annotation, based on our ITPR1 transcript expression data, greatly facilitated analysis. Genotype-phenotype associations were highly variable. Importantly, while cerebellar atrophy was common, cerebellar volume loss did not correlate with symptom progression.

CONCLUSIONS

This dataset represents the largest cohort of patients with ITPR1 missense variants, expanding the clinical spectrum of SCA29 and GLSP. Standardized transcript annotation is essential for future reporting. Our findings will aid in diagnostic interpretation in the clinic and guide selection of variants for preclinical studies. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

ITPR1-associated spinocerebellar ataxia with craniofacial features-additional evidence for germline mosaicism

Inositol 1,4,5-triphosphate receptor type 1 (ITPR1) is an endoplasmic reticulum-bound intracellular inositol triphosphate receptor involved in the regulation of intracellular calcium. Pathogenic variants in ITPR1 are associated with spinocerebellar ataxia (SCA) types 15/16 and 29 and have recently been implicated in a facial microsomia syndrome. In this report, we present a family with three affected individuals found to have a heterozygous missense c.800C > T (predicted p.Thr267Met) who present clinically with a SCA29-like syndrome. All three individuals presented with varying degrees of ataxia, developmental delay, and apparent intellectual disability, as well as craniofacial involvement-an uncommon finding in patients with SCA29. The variant was identified using clinical exome sequencing and validated with Sanger sequencing. It is presumed to be inherited via parental germline mosaicism. We present our findings to provide additional evidence for germline mosaic inheritance of SCA29, as well as to expand the clinical phenotype of the syndrome.