Calpain 12 Function Revealed through the Study of an Atypical Case of Autosomal Recessive Congenital Ichthyosis

Alopecia patterns and trichoscopic findings in patients with autosomal recessive congenital ichthyosis

Background

Autosomal recessive congenital ichthyosis (ARCI) is a rare genodermatosis categorized among nonsyndromic ichthyoses. While ARCI patients often manifest hair abnormalities, their impact on the quality of life remains underreported in the literature.

Objective

This study aims to comprehensively characterize the clinical and trichoscopic findings of alopecia in ARCI patients.

Methods

A prospective study spanning from January 2019 to December 2021 (3 years) was conducted at the Dermatology Department of Habib Thameur Hospital, Tunis, Tunisia. Clinical and trichoscopic examinations were performed on the hair of the participants, with molecular studies conducted on 15 patients.

Results

The study included 30 patients, predominantly female (male/female = 0.58), with a mean age of 20 years. Twenty-eight patients were born from consanguineous marriages. Lamellar ichthyosis was observed in 22 cases, while congenital ichthyosiform erythroderma and bathing suit ichthyosis were each present in 4 cases. The ARCI severity score, assessed using the Visual Index For Ichthyosis Severity scale, had a mean value of 15 (4-28). Alopecia emerged as a prominent finding in 11 patients, presenting as hairline recession (13%), multiple patchy alopecia (27%), and alopecia of the eyebrows (13%). Trichoscopic findings included interfollicular and perifollicular scaling, perifollicular lamellar hyperkeratosis, peripilar casts, interfollicular erythema, loss of hair openings, predominance of single hair follicles, broken hair, vellus hair, anisotrichosis, pili torti, dystrophic hair, and comma hair. Several trichoscopic findings showed statistically significant associations with the severity of ARCI.

Limitations

In our study, we only included 30 patients due to the rarity of this genodermatosis.

Conclusion

Contrary to previous perceptions, alopecia is a notable finding in ARCI, particularly in patients with a severe form. This study provides a detailed characterization of alopecia in ARCI, shedding light on its prevalence and associated trichoscopic features, thereby enhancing our understanding of this dermatological condition.

Proteolytic and Antiproteolytic Activity in the Skin: Gluing the Pieces Together

Epidermal differentiation is ultimately aimed at the formation of a functional barrier capable of protecting the organism from the environment while preventing loss of biologically vital elements. Epidermal differentiation entails a delicately regulated process of cell-cell junction formation and dissolution to enable upward cell migration and desquamation. Over the past two decades, the deciphering of the genetic basis of a number of inherited conditions has delineated the pivotal role played in this process by a series of proteases and protease inhibitors, including serpins, cathepsins, and cystatins, suggesting novel avenues for therapeutic intervention in both rare and common disorders of cornification.

Calpain activity is negatively regulated by a KCTD7-Cullin-3 complex via non-degradative ubiquitination

Calpains are a class of non-lysosomal cysteine proteases that exert their regulatory functions via limited proteolysis of their substrates. Similar to the lysosomal and proteasomal systems, calpain dysregulation is implicated in the pathogenesis of neurodegenerative disease and cancer. Despite intensive efforts placed on the identification of mechanisms that regulate calpains, however, calpain protein modifications that regulate calpain activity are incompletely understood. Here we show that calpains are regulated by KCTD7, a cytosolic protein of previously uncharacterized function whose pathogenic mutations result in epilepsy, progressive ataxia, and severe neurocognitive deterioration. We show that KCTD7 works in complex with Cullin-3 and Rbx1 to execute atypical, non-degradative ubiquitination of calpains at specific sites (K398 of calpain 1, and K280 and K674 of calpain 2). Experiments based on single-lysine mutants of ubiquitin determined that KCTD7 mediates ubiquitination of calpain 1 via K6-, K27-, K29-, and K63-linked chains, whereas it uses K6-mediated ubiquitination to modify calpain 2. Loss of KCTD7-mediated ubiquitination of calpains led to calpain hyperactivation, aberrant cleavage of downstream targets, and caspase-3 activation. CRISPR/Cas9-mediated knockout of Kctd7 in mice phenotypically recapitulated human KCTD7 deficiency and resulted in calpain hyperactivation, behavioral impairments, and neurodegeneration. These phenotypes were largely prevented by pharmacological inhibition of calpains, thus demonstrating a major role of calpain dysregulation in KCTD7-associated disease. Finally, we determined that Cullin-3-KCTD7 mediates ubiquitination of all ubiquitous calpains. These results unveil a novel mechanism and potential target to restrain calpain activity in human disease and shed light on the molecular pathogenesis of KCTD7-associated disease.

Ichthyosis

The ichthyoses are a large, heterogeneous group of skin cornification disorders. They can be inherited or acquired, and result in defective keratinocyte differentiation and abnormal epidermal barrier formation. The resultant skin barrier dysfunction leads to increased transepidermal water loss and inflammation. Disordered cornification is clinically characterized by skin scaling with various degrees of thickening, desquamation (peeling) and erythema (redness). Regardless of the type of ichthyosis, many patients suffer from itching, recurrent infections, sweating impairment (hypohidrosis) with heat intolerance, and diverse ocular, hearing and nutritional complications that should be monitored periodically. The characteristic clinical features are considered to be a homeostatic attempt to repair the skin barrier, but heterogeneous clinical presentation and imperfect phenotype-genotype correlation hinder diagnosis. An accurate molecular diagnosis is, however, crucial for predicting prognosis and providing appropriate genetic counselling. Most ichthyoses severely affect patient quality of life and, in severe forms, may cause considerable disability and even death. So far, treatment provides only symptomatic relief. It is lifelong, expensive, time-consuming, and often provides disappointing results. A better understanding of the molecular mechanisms that underlie these conditions is essential for designing pathogenesis-driven and patient-tailored innovative therapeutic solutions.

Calpain-mediated proteolysis as driver and modulator of polyglutamine toxicity

Among posttranslational modifications, directed proteolytic processes have the strongest impact on protein integrity. They are executed by a variety of cellular machineries and lead to a wide range of molecular consequences. Compared to other forms of proteolytic enzymes, the class of calcium-activated calpains is considered as modulator proteases due to their limited proteolytic activity, which changes the structure and function of their target substrates. In the context of neurodegeneration and - in particular - polyglutamine disorders, proteolytic events have been linked to modulatory effects on the molecular pathogenesis by generating harmful breakdown products of disease proteins. These findings led to the formulation of the toxic fragment hypothesis, and calpains appeared to be one of the key players and auspicious therapeutic targets in Huntington disease and Machado Joseph disease. This review provides a current survey of the role of calpains in proteolytic processes found in polyglutamine disorders. Together with insights into general concepts behind toxic fragments and findings in polyglutamine disorders, this work aims to inspire researchers to broaden and deepen the knowledge in this field, which will help to evaluate calpain-mediated proteolysis as a unifying and therapeutically targetable posttranslational mechanism in neurodegeneration.

Nail Involvement in Autosomal Recessive Congenital Ichthyosis

Autosomal recessive congenital ichthyosis (ARCI) is a clinically and genetically heterogeneous category of non-syndromic ichthyosis (2). Nail changes in ARCI are generally frequent but have been rarely reported and studied in the literature. This stimulated us to conduct a study to describe nail changes in ARCI using a combined literature review and prospective examination from March 2019 to August 2019 (6 months) in the Dermatology Department of Habib Thameur Hospital, Tunis, Tunisia. A total of twenty-five patients with ARCI had a clinical and dermatoscopic review. Mean age was 19.8 years old [range 1-43], with a female predominance- 17 women (68%) and 8 men (32%). Seventy-two percent had nail unit changes involving more than one nail, none with single nail disease, involvement of fingernails (64%) and toenails (68%) cases including periungual hyperkeratosis (64%), xanthonychia (40%), pachyonychia (40%), macrolunula (36%), digital clubbing (32%) and onychomycosis (24%). Rarer findings included pseudoainhum, transverse leukonychia, longitudinal melanonychia, and subungual hemorrhages each in one patient (4%). There was a statistically significant increased frequency of nail changes in adults over children (p = 0.001). Nail abnormalities statistically associated with ARCI were macrolunula, periungual hyperkeratosis, xanthonychia, and pachyonychia. A comprehensive review of the literature was performed, creating the first comprehensive review addressing nail disease in ARCI.

Molecular epidemiology of non-syndromic autosomal recessive congenital ichthyosis in a Middle-Eastern population

Autosomal recessive congenital ichthyosis (ARCI) is a rare and heterogeneous skin cornification disorder presenting with generalized scaling and varying degrees of erythema. Clinical manifestations range from lamellar ichthyosis (LI), congenital ichthyosiform erythroderma (CIE) through the most severe form of ARCI, Harlequin ichthyosis (HI). We used homozygosity mapping, whole-exome and direct sequencing to delineate the relative distribution of pathogenic variants as well as identify genotype-phenotype correlations in a cohort of 62 Middle Eastern families with ARCI of various ethnic backgrounds. Pathogenic variants were identified in most ARCI-associated genes including TGM1 (21%), CYP4F22 (18%), ALOX12B (14%), ABCA12 (10%), ALOXE3 (6%), NIPAL4 (5%), PNPLA1 (3%), LIPN (2%) and SDR9C7 (2%). In 19% of cases, no mutation was identified. Our cohort revealed a higher prevalence of CYP4F22 and ABCA12 pathogenic variants and a lower prevalence of TGM1 and NIPAL4 variants, as compared to data obtained in other regions of the world. Most variants (89%) in ALOX12B were associated with CIE and were the most common cause of ARCI among patients of Muslim origin (26%). Palmoplantar keratoderma associated with fissures was exclusively a result of pathogenic variants in TGM1. To our knowledge, this is the largest cohort study of ARCI in the Middle-Eastern population reported to date. Our data demonstrate the importance of population-tailored mutation screening strategies and shed light upon specific genotype-phenotype correlations.

Identification of clinically useful predictive genetic variants in pachyonychia congenita

BACKGROUND

Pachyonychia congenita (PC) refers to a group of autosomal dominant disorders caused by mutations in five keratin genes (KRT16,KRT6A,KRT17,KRT6B or KRT6C). Current disease classification is based on the gene harbouring disease-causing variants.

AIMS

We harnessed the International Pachyonychia Congenita Research Registry (IPCRR) containing both clinical and molecular data on patients with PC worldwide, to identify genetic variants predicting disease severity.

METHODS

We ascertained 815 individuals harbouring keratin mutations registered in the IPCRR. We looked for statistically significant associations between genetic variants and clinical manifestations in a subgroup of patients carrying mutations found in at least 10% of the cohort. Data were analysed using χ² and Kruskal-Wallis tests.

RESULTS

We identified five mutations occurring in at least 10% of the patients registered in the IPCRR. The KRT16 p.L132P mutation was significantly associated with younger age of onset, presence of palmar keratoderma oral leucokeratosis and a higher number of involved nails. By contrast, the KRT16 p.N125S and p.R127C mutations resulted in a milder phenotype featuring a decreased number of involved nails and older age of onset. Patients carrying the p.N125S mutation were less likely to develop palmar keratoderma while p.R127C was associated with an older age of palmoplantar keratoderma onset. Moreover, the KRT17 p.L99P mutation resulted in an increased number of involved fingernails and patients demonstrating 20-nail dystrophy, while the opposite findings were observed with KRT17 p.N92S mutation.

CONCLUSIONS

We have identified novel and clinically useful genetic predictive variants in the largest cohort of patients with PC described to date.

Calpains for dummies: What you need to know about the calpain family

This review was written in memory of our late friend, Dr. Hiroyuki Sorimachi, who, following the steps of his mentor Koichi Suzuki, a pioneer in calpain research, has made tremendous contributions to the field. During his career, Hiro also wrote several reviews on calpain, the last of which, published in 2016, was comprehensive. In this manuscript, we decided to put together a review with the basic information a novice may need to know about calpains. We also tried to avoid similarities with previous reviews and reported the most significant new findings, at the same time highlighting Hiro's contributions to the field. The review will cover a short history of calpain discovery, the presentation of the family, the life of calpain from transcription to activity, human diseases caused by calpain mutations and therapeutic perspectives.

Effects of functionally diverse calpain system on immune cells

Calpains are a family of nonlysosomal cysteine proteases, which play important roles in numerous physiological and pathological processes. Locations of them dictates the functions so that they are classified as ubiquitously expressed calpains and tissue-specific calpains. Recent studies are mainly focused on conventional calpains (calpain-1,2) in development and diseases, and increasing people pay attention to other subtypes of calpains but may not been summarized appropriately. Growing evidence suggests that calpains are also involved in immune regulation. However, seldom articles review the regulation of calpains on immune cells. The aim of this article is to review the research progress of each calpain isozyme and the effect of calpains on immune cells, especially the promotion effect of calpains on the immune response of macrophage, neutrophils, dendritic cells, mast cells, natural killed cells, and lymphocytes. These effects would hold great promise for the clinical application of calpains as a practicable therapeutic option in the treatment of immune related diseases.

Calpain-calpastatin system and cancer progression

The calpain system is required by many important physiological processes, including the cell cycle, cytoskeleton remodelling, cellular proliferation, migration, cancer cell invasion, metastasis, survival, autophagy, apoptosis and signalling, as well as the pathogenesis of a wide range of disorders, in which it may function to promote tumorigenesis. Calpains are intracellular conserved calcium-activated neutral cysteine proteinases that are involved in mediating cancer progression via catalysing and regulating the proteolysis of their specific substrates, which are important signalling molecules during cancer progression. μ-calpain, m-calpain, and their specific inhibitor calpastatin are the three molecules originally identified as comprising the calpain system and they contain several crucial domains, specific motifs, and functional sites. A large amount of data supports the roles of the calpain-calpastatin system in cancer progression via regulation of cellular adhesion, proliferation, invasion, metastasis, and cellular survival and death, as well as inflammation and angiogenesis during tumorigenesis, implying that the inhibition of calpain activity may be a potential anti-cancer intervention strategy targeting cancer cell survival, invasion and chemotherapy resistance.

Phenotypic suppression of acral peeling skin syndrome in a patient with autosomal recessive congenital ichthyosis

Autosomal recessive congenital ichthyosis (ARCI) manifests with generalized scaling often associated with generalized erythema. Mutations in at least 13 different genes have been reported to cause ARCI. Acral peeling skin syndrome (APSS) is a rare autosomal recessive disorder manifesting with peeling over the distal limbs and dorsal surfaces of hands and feet. APSS is mostly due to mutations in TGM5, encoding transglutaminase 5. Both ARCI and APSS are fully penetrant genetic traits. Here, we describe a consanguineous family in which one patient with mild ARCI was found to carry a homozygous mutation in ALOXE3 (c.1238G > A; p.Gly413Asp). The patient was also found to carry a known pathogenic homozygous mutation in TGM5 (c.1335G > C; p.Lys445Asn) but did not display acral peeling skin. Her uncle carried the same homozygous mutation in TGM5 but carried the ALOXE3 mutation in a heterozygous state and showed clinical features typical of APSS. Taken collectively, these observations suggested that the ALOXE3 mutation suppresses the clinical expression of the TGM5 variant. We hypothesized that ALOXE3 deficiency may affect the expression of a protein capable of compensating for the lack of TGM5 expression. Downregulation of ALOXE3 in primary human keratinocytes resulted in increased levels of corneodesmosin, which plays a critical role in the maintenance of cell-cell adhesion in the upper epidermal layers. Accordingly, ectopic corneodesmosin expression rescued the cell-cell adhesion defect caused by TGM5 deficiency in keratinocytes as ascertained by the dispase dissociation assay. The present data thus provide evidence for phenotypic suppression in a human hereditary skin disorder.

A novel ABCA12 pathologic variant identified in an Ecuadorian harlequin ichthyosis patient: A step forward in genotype-phenotype correlations

Background

Autosomal recessive congenital ichthyoses (ARCI) have been associated with different phenotypes including: harlequin ichthyosis (HI), congenital ichthyosiform erythroderma (CIE), and lamellar ichthyosis (LI). While pathogenic variants in all ARCI genes are associated with LI and CIE phenotypes, the unique gene associated with HI is ABCA12. In HI, the most severe ARCI form, pathogenic variants in both ABCA12 gene alleles usually have a severe impact on protein function. The presence of at least one non‐truncating variant frequently causes a less severe congenital ichthyosis phenotype (LI and CIE).

Methods

We report the case of a 4‐year‐old Ecuadorian boy with a severe skin disease. Genetic diagnosis was performed by NGS. In silico predictions were performed using Alamut software v2.11. A review of the literature was carried out to identify all patients carrying ABCA12 splice‐site and missense variants, and to explore their genotype‐phenotype correlations.

Results

Genetic testing revealed a nonsense substitution, p.(Arg2204*), and a new missense variant, p.(Val1927Leu), in the ABCA12 gene. After performing in silico analysis and a comprehensive review of the literature, we conclude that p.(Val1927Leu) affects a well conserved residue which could either disturb the protein function or alter the splicing process, both alternatives could explain the severe phenotype of our patient.

Conclusion

This case expands the spectrum of ABCA12 reported disease‐causing variants which is important to unravel genotype‐phenotype correlations and highlights the importance of missense variants in the development of HI.

Killing Two Angry Birds with One Stone: Autophagy Activation by Inhibiting Calpains in Neurodegenerative Diseases and Beyond

Proteolytic machineries execute vital cellular functions and their disturbances are implicated in diverse medical conditions, including neurodegenerative diseases. Interestingly, calpains, a class of Ca²⁺-dependent regulatory proteases, can modulate the degradational system of autophagy by cleaving proteins involved in this pathway. Moreover, both machineries are common players in many molecular pathomechanisms and have been targeted individually or together, as a therapeutic strategy in experimental setups. In this review, we briefly introduce calpains and autophagy, with their roles in health and disease, and focus on their direct pathologically relevant interplay in neurodegeneration and beyond. The modulation of calpain activity may comprise a promising treatment approach to attenuate the deregulation of these two essential mechanisms.

Clinical Application of Genome and Exome Sequencing as a Diagnostic Tool for Pediatric Patients: a Scoping Review of the Literature

PURPOSE

Availability of clinical genomic sequencing (CGS) has generated questions about the value of genome and exome sequencing as a diagnostic tool. Analysis of reported CGS application can inform uptake and direct further research. This scoping literature review aims to synthesize evidence on the clinical and economic impact of CGS.

METHODS

PubMed, Embase, and Cochrane were searched for peer-reviewed articles published between 2009 and 2017 on diagnostic CGS for infant and pediatric patients. Articles were classified according to sample size and whether economic evaluation was a primary research objective. Data on patient characteristics, clinical setting, and outcomes were extracted and narratively synthesized.

RESULTS

Of 171 included articles, 131 were case reports, 40 were aggregate analyses, and 4 had a primary economic evaluation aim. Diagnostic yield was the only consistently reported outcome. Median diagnostic yield in aggregate analyses was 33.2% but varied by broad clinical categories and test type.

CONCLUSION

Reported CGS use has rapidly increased and spans diverse clinical settings and patient phenotypes. Economic evaluations support the cost-saving potential of diagnostic CGS. Multidisciplinary implementation research, including more robust outcome measurement and economic evaluation, is needed to demonstrate clinical utility and cost-effectiveness of CGS.

Calpain research for drug discovery: challenges and potential

Calpains are a family of proteases that were scientifically recognized earlier than proteasomes and caspases, but remain enigmatic. However, they are known to participate in a multitude of physiological and pathological processes, performing 'limited proteolysis' whereby they do not destroy but rather modulate the functions of their substrates. Calpains are therefore referred to as 'modulator proteases'. Multidisciplinary research on calpains has begun to elucidate their involvement in pathophysiological mechanisms. Therapeutic strategies targeting malfunctions of calpains have been developed, driven primarily by improvements in the specificity and bioavailability of calpain inhibitors. Here, we review the calpain superfamily and calpain-related disorders, and discuss emerging calpain-targeted therapeutic strategies.