Nucleotide substitutions at the p.Gly117 and p.Thr180 mutational hot-spots of SKI alter molecular dynamics and may affect cell cycle

Heterozygous deleterious variants in SKI cause Shprintzen-Goldberg Syndrome, which is mainly characterized by craniofacial features, neurodevelopmental disorder and thoracic aorta dilatations/aneurysms. The encoded protein is a member of the transforming growth factor beta signaling. Paucity of reported studies exploring the SGS molecular pathogenesis hampers disease recognition and clinical interpretation of private variants. Here, the unpublished c.349G>A, p.[Gly117Ser] and the recurrent c.539C>T, p.[Thr180Met] SKI variants were studied combining in silico and in vitro approach. 3D comparative modeling and calculation of the interaction energy predicted that both variants alter the SKI tertiary protein structure and its interactions. Computational data were functionally corroborated by the demonstration of an increase of MAPK phosphorylation levels and alteration of cell cycle in cells expressing the mutant SKI. Our findings confirmed the effects of SKI variants on MAPK and opened the path to study the role of perturbations of the cell cycle in SGS.

The ubiquitin ligase TRIM32 promotes the autophagic response to Mycobacterium tuberculosis infection in macrophages

Mycobacterium tuberculosis (Mtb) is known to evade host immune responses and persist in macrophages for long periods. A mechanism that the host uses to combat Mtb is xenophagy, a selective form of autophagy that targets intracellular pathogens for degradation. Ubiquitination of Mtb or Mtb-containing compartments is a key event to recruit the autophagy machinery and mediate the bacterial delivery to the lysosome. This event relies on the coordinated and complementary activity of different ubiquitin ligases, including PARKIN, SMURF1, and TRIM16. Because each of these factors is responsible for the ubiquitination of a subset of the Mtb population, it is likely that additional ubiquitin ligases are employed by macrophages to trigger a full xenophagic response during Mtb infection. In this study, we investigated the role TRIM proteins whose expression is modulated in response to Mtb or BCG infection of primary macrophages. These TRIMs were ectopically expressed in THP1 macrophage cell line to assess their impact on Mtb replication. This screening identified TRIM32 as a novel player involved in the intracellular response to Mtb infection, which promotes autophagy-mediated Mtb degradation. The role of TRIM32 in xenophagy was further confirmed by silencing TRIM32 expression in THP1 cells, which causes increased intracellular growth of Mtb associated to impaired Mtb ubiquitination, reduced recruitment of the autophagy proteins NDP52/CALCOCO2 and BECLIN 1/BECN1 to Mtb and autophagosome formation. Overall, these findings suggest that TRIM32 plays an important role in the host response to Mtb infection through the induction of autophagy, representing a promising target for host-directed tuberculosis therapies.

Specifications and validation of the ACMG/AMP criteria for clinical interpretation of sequence variants in collagen genes associated with joint hypermobility

Deleterious variants in collagen genes are the most common cause of hereditary connective tissue disorders (HCTD). Adaptations of the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) criteria are still lacking. A multidisciplinary team was set up for developing specifications of the ACMG/AMP criteria for COL1A1, COL1A2, COL2A1, COL3A1, COL5A1, COL5A2, COL11A1, COL11A2 and COL12A1, associated with various forms of HCTD featuring joint hypermobility, which is becoming one of the most common reasons of referral for molecular testing in this field. Such specifications were validated against 209 variants, and resulted effective for classifying as pathogenic and likely pathogenic null alleles without downgrading of the PVS1 level of strength and recurrent Glycine substitutions. Adaptations of selected criteria reduced uncertainties on private Glycine substitutions, intronic variants predicted to affect the splicing, and null alleles with a downgraded PVS1 level of strength. Segregation and multigene panel sequencing data mitigated uncertainties on non-Glycine substitutions by the attribution of one or more benignity criteria. These specifications may improve the clinical utility of molecular testing in HCTD by reducing the number of variants with neutral/conflicting interpretations. Close interactions between laboratory and clinicians are crucial to estimate the a priori utility of molecular test and to improve medical reports.

Amplification of protease-activated receptors signaling in sporadic cerebral cavernous malformation endothelial cells

In the central nervous system, thrombin-mediated activation of protease-activated receptors (PARs) results in neuroinflammation and increased vascular permeability. These events have been linked to cancer and neurodegeneration. Endothelial cells (ECs) isolated from sporadic cerebral cavernous malformation (CCM) specimens showed dysregulation of genes involved in "thrombin-mediated PAR-1 activation" signaling. CCM is a vascular disease involving brain capillaries. In CCM, ECs show defective cell junctions. Oxidative stress and neuroinflammation play a key role in disease onset and progression. In order to confirm the possible role of thrombin pathway in sporadic CCM pathogenesis, we evaluated PARs expression in CCM-ECs. We found that sporadic CCM-ECs overexpress PAR1, PAR3 and PAR4, together with other coagulation factor encoding genes. Moreover, we investigated about expression of the three familial CCM genes (KRIT1, CCM2 and PDCD10) in human cerebral microvascular ECs, following thrombin exposure, as well as protein level. Thrombin exposure affects EC viability and results in dysregulation of CCM gene expression and, then, in decreased protein level. Our results confirm amplification of PAR pathway in CCM suggesting, for the first time, the possible role of PAR1-mediated thrombin signaling in sporadic CCM. Thrombin-mediated PARs over activation results in increased blood-brain barrier permeability due to loss of cell junction integrity and, in this context, also the three familial CCM genes may be involved.

Safety and efficacy of propranolol for treatment of familial cerebral cavernous malformations (Treat_CCM): a randomised, open-label, blinded-endpoint, phase 2 pilot trial

BACKGROUND

Observations in people with cerebral cavernous malformations, and in preclinical models of this disorder, suggest that the β-blocker propranolol might reduce the risk of intracerebral haemorrhage. We aimed to evaluate the safety and efficacy of prolonged treatment with propranolol to reduce the incidence of symptomatic intracerebral haemorrhage or focal neurological deficit in people with familial cerebral cavernous malformations.

METHODS

We conducted a randomised, open-label, blinded-endpoint, phase 2 pilot trial (Treat_CCM) at six national reference centres for rare diseases in Italy. People aged 18 years or older with symptomatic familial cerebral cavernous malformation were eligible for enrolment. Participants were randomly assigned (2:1) to receive either oral propranolol (20-320 mg daily) plus standard care (intervention group), or standard care alone (control group), for 24 months. Participants, caregivers, and investigators were aware of treatment group assignment. Participants had clinical assessments and 3 T brain MRI at baseline and at 12 and 24 months. The primary outcome was new occurrence of symptomatic intracerebral haemorrhage or focal neurological deficit attributable to cerebral cavernous malformation over 24 months. Outcome assessors were masked to treatment group assignment. The primary analysis was done in the intention-to-treat population. Because of the pilot study design, we chose a one-sided 80% CI, which could either exclude a clinically meaningful effect or show a signal of efficacy. This trial is registered with EudraCT, 2017-003595-30, and ClinicalTrials.gov, NCT03589014, and is closed to recruitment.

FINDINGS

Between April 11, 2018, and Dec 5, 2019, 95 people were assessed for eligibility and 83 were enrolled, of whom 57 were assigned to the propranolol plus standard care group and 26 to the standard care alone group. The mean age of participants was 46 years (SD 15); 48 (58%) were female and 35 (42%) were male. The incidence of symptomatic intracerebral haemorrhage or focal neurological deficit was 1·7 (95% CI 1·4-2·0) cases per 100 person-years (two [4%] of 57 participants) in the propranolol plus standard care group and 3·9 (3·1-4·7) per 100 person-years (two [8%] of 26) in the standard care alone group (univariable hazard ratio [HR] 0·43, 80% CI 0·18-0·98). The univariable HR showed a signal of efficacy, according to predefined criteria. The incidence of hospitalisation did not differ between groups (8·2 cases [95% CI 7·5-8·9] per 100 person-years in the propranolol plus standard care group vs 8·2 [95% CI 7·1-9·3] per 100 person-years in the standard care alone group). One participant in the standard care alone group died of sepsis. Three participants in the propranolol plus standard care group discontinued propranolol due to side-effects (two reported hypotension and one reported weakness).

INTERPRETATION

Propranolol was safe and well tolerated in this population. Propranolol might be beneficial for reducing the incidence of clinical events in people with symptomatic familial cerebral cavernous malformations, although this trial was not designed to be adequately powered to investigate efficacy. A definitive phase 3 trial of propranolol in people with symptomatic familial cerebral cavernous malformations is justified.

FUNDING

Italian Medicines Agency, Associazione Italiana per la Ricerca sul Cancro, Swedish Science Council, Knut and Alice Wallenberg Foundation, CARIPLO Foundation, Italian Ministry of Health.

Downexpression of miR-200c-3p Contributes to Achalasia Disease by Targeting the PRKG1 Gene

Achalasia is an esophageal smooth muscle motility disorder with unknown pathogenesis. Taking into account our previous results on the downexpression of miR-200c-3p in tissues of patients with achalasia correlated with an increased expression of PRKG1, SULF1, and SYDE1 genes, our aim was to explore the unknown biological interaction between these genes and human miR-200c-3p and if this relation could unravel their functional role in the etiology of achalasia. To search for putative miR-200c-3p binding sites in the 3'-UTR of PRKG1, SULF1 and SYDE1, a bioinformatics tool was used. To test whether PRKG1, SULF1, and SYDE1 are targeted by miR-200c-3p, a dual-luciferase reporter assay and quantitative PCR on HEK293 and fibroblast cell lines were performed. To explore the biological correlation between PRKG1 and miR-200c-3p, an immunoblot analysis was carried out. The overexpression of miR-200c-3p reduced the luciferase activity in cells transfected with a luciferase reporter containing a fragment of the 3'-UTR regions of PRKG1, SULF1, and SYDE1 which included the miR-200c-3p seed sequence. The deletion of the miR-200c-3p seed sequence from the 3'-UTR fragments abrogated this reduction. A negative correlation between miR-200c-3p and PRKG1, SULF1, and SYDE1 expression levels was observed. Finally, a reduction of the endogenous level of PRKG1 in cells overexpressing miR-200c-3p was detected. Our study provides, for the first time, functional evidence about the PRKG1 gene as a direct target and SULF1 and SYDE1 as potential indirect substrates of miR-200c-3p and suggests the involvement of NO/cGMP/PKG signaling in the pathogenesis of achalasia.

Transcriptome Analysis Reveals Altered Expression of Genes Involved in Hypoxia, Inflammation and Immune Regulation in Pdcd10-Depleted Mouse Endothelial Cells

Cerebral cavernous malformations (CCM) are capillary malformations affecting the central nervous system and commonly present with headaches, epilepsy and stroke. Treatment of CCM is symptomatic, and its prevention is limited. CCM are often sporadic but sometimes may be multifocal and/or affect multiple family members. Heterozygous pathogenic variants in PDCD10 cause the rarest and apparently most severe genetic variant of familial CCM. We carried out an RNA-Seq and a Q-PCR validation analysis in Pdcd10-silenced and wild-type mouse endothelial cells in order to better elucidate CCM molecular pathogenesis. Ninety-four differentially expressed genes presented an FDR-corrected p-value < 0.05. A functionally clustered dendrogram showed that differentially expressed genes cluster in cell proliferation, oxidative stress, vascular processes and immune response gene-ontology functions. Among differentially expressed genes, the major cluster fell in signaling related to inflammation and pathogen recognition, including HIF1α and Nos2 signaling and immune regulation. Validation analysis performed on wild-type, Pdcd10-null and Pdcd10-null reconstituted cell lines was consistent with RNA-Seq data. This work confirmed previous mouse transcriptomic data in endothelial cells, which are recognized as a critical tissue for CCM formation and expands the potential molecular signatures of PDCD10-related familial CCM to alterations in inflammation and pathogen recognition pathways.

In Vitro Assays for the Bifunctional Acylpeptide Hydrolase (APEH) Enzyme from Antarctic Fish

The bifunctional enzyme acylpeptide hydrolase (APEH) is involved in important metabolic processes both as an exopeptidase and as an endopeptidase. Hence, the growing interest in the study of this protein and the need to set up in vitro assays for its characterization. This chapter describes two in vitro assays able to detect the activities of APEH, one for the exopeptidase activity and one for the endopeptidase activity. In particular, these assays have been set up on the two APEH isoforms from Antarctic fish, characterized by a distinct functionality and marked exo- and endopeptidase activities.

Oxidized Substrates of APEH as a Tool to Study the Endoprotease Activity of the Enzyme

APEH is a ubiquitous and cytosolic serine protease belonging to the prolyl oligopeptidase (POP) family, playing a critical role in the processes of degradation of proteins through both exo- and endopeptidase events. Endopeptidase activity has been associated with protein oxidation; however, the actual mechanisms have yet to be elucidated. We show that a synthetic fragment of GDF11 spanning the region 48–64 acquires sensitivity to the endopeptidase activity of APEH only when the methionines are transformed into the corresponding sulphoxide derivatives. The data suggest that the presence of sulphoxide-modified methionines is an important prerequisite for the substrates to be processed by APEH and that the residue is crucial for switching the enzyme activity from exo- to endoprotease. The cleavage occurs on residues placed on the C-terminal side of Met(O), with an efficiency depending on the methionine adjacent residues, which thereby may play a crucial role in driving and modulating APEH endoprotease activity.

Loss-of-function variants in exon 4 of TAB2 cause a recognizable multisystem disorder with cardiovascular, facial, cutaneous, and musculoskeletal involvement

PURPOSE

This study aimed to describe a multisystemic disorder featuring cardiovascular, facial, musculoskeletal, and cutaneous anomalies caused by heterozygous loss-of-function variants in TAB2.

METHODS

Affected individuals were analyzed by next-generation technologies and genomic array. The presumed loss-of-function effect of identified variants was assessed by luciferase assay in cells transiently expressing TAB2 deleterious alleles. In available patients' fibroblasts, variant pathogenicity was further explored by immunoblot and osteoblast differentiation assays. The transcriptomic profile of fibroblasts was investigated by RNA sequencing.

RESULTS

A total of 11 individuals from 8 families were heterozygotes for a novel TAB2 variant. In total, 7 variants were predicted to be null alleles and 1 was a missense change. An additional subject was heterozygous for a 52 kb microdeletion involving TAB2 exons 1 to 3. Luciferase assay indicated a decreased transcriptional activation mediated by NF-κB signaling for all point variants. Immunoblot analysis showed a reduction of TAK1 phosphorylation while osteoblast differentiation was impaired. Transcriptomic analysis identified deregulation of multiple pleiotropic pathways, such as TGFβ-, Ras-MAPK-, and Wnt-signaling networks.

CONCLUSION

Our data defined a novel disorder associated with loss-of-function or, more rarely, hypomorphic alleles in a restricted linker region of TAB2. The pleiotropic manifestations in this disorder partly recapitulate the 6q25.1 (TAB2) microdeletion syndrome and deserve the definition of cardio-facial-cutaneous-articular syndrome.

Ehlers-Danlos Syndromes, Joint Hypermobility and Hypermobility Spectrum Disorders

Ehlers-Danlos syndrome is an umbrella term for a clinically and genetically heterogeneous group of hereditary soft connective tissue disorders mainly featuring abnormal cutaneous texture (doughy/velvety, soft, thin, and/or variably hyperextensible skin), easy bruising, and joint hypermobility. Currently, musculoskeletal manifestations related to joint hypermobility are perceived as the most prevalent determinants of the quality of life of affected individuals. The 2017 International Classification of Ehlers-Danlos syndromes and related disorders identifies 13 clinical types due to deleterious variants in 19 different genes. Recent publications point out the possibility of a wider spectrum of conditions that may be considered members of the Ehlers-Danlos syndrome community. Most Ehlers-Danlos syndromes are due to inherited abnormalities affecting the biogenesis of fibrillar collagens and other components of the extracellular matrix. The introduction of next-generation sequencing technologies in the diagnostic setting fastened patients' classification and improved our knowledge on the phenotypic variability of many Ehlers-Danlos syndromes. This is impacting significantly patients' management and family counseling. At the same time, most individuals presenting with joint hypermobility and associated musculoskeletal manifestations still remain without a firm diagnosis, due to a too vague clinical presentation and/or the lack of an identifiable molecular biomarker. These individuals are currently defined with the term "hypermobility spectrum disorders". Hence, in parallel with a continuous update of the International Classification of Ehlers-Danlos syndromes, the scientific community is investing efforts in offering a more efficient framework for classifying and, hopefully, managing individuals with joint hypermobility.

Improving clinical interpretation of five KRIT1 and PDCD10 intronic variants

Cerebral cavernous malformation (CCM) is a vascular malformation of the central nervous system which may occur sporadically or segregate within families due to heterozygous variants in KRIT1/CCM1, MGC4607/CCM2 or PDCD10/CCM3. Intronic variants are not uncommon in familial CCM, but their clinical interpretation is often hampered by insufficient data supporting in silico predictions. Here, the mRNA analysis for two intronic unpublished variants (KRIT1 c.1147-7 T > G and PDCD10 c.395 + 2 T > G) and three previously published variants in KRIT1 but without data supporting their effects was carried out. This study demonstrated that all variants can induce a frameshift with the lack of residues located in the C-terminal regions and involved in protein-protein complex formation, which is essential for vascular homeostasis. These results support the introduction of mRNA analysis in the diagnostic pathway of familial CCM and expand the knowledge of abnormal splicing patterning in this disorder.

Review of clinical and molecular variability in autosomal recessive cutis laxa 2A

ATP6V0A2-related cutis laxa, also known as autosomal recessive cutis laxa type 2A (ARCL2A), is a subtype of hereditary cutis laxa originally characterized by skin, skeletal, and neurological involvement, and a combined defect of N-glycosylation and O-glycosylation. The associated clinical spectrum subsequently expanded to a less severe phenotype dominated by cutaneous involvement. At the moment, ARCL2A was described in a few case reports and series only. An Italian adult woman ARCL2A with a phenotype restricted to skin and the two novel c.3G>C and c.1101dup ATP6V0A2 variants has been reported. A systematic literature review allowed us to identify 69 additional individuals from 64 families. Available data were scrutinized in order to describe the clinical and molecular variability of ARCL2A. About 78.3% of known variants were predicted null alleles, while 11 were missense and 2 affected noncanonical splice sites. Age at ascertainment appeared as the unique phenotypic discriminator with earlier age more commonly associated with facial dysmorphism (p .02), high/cleft palate (p .005), intellectual disability/global developmental delay (p .013), and seizures (p .024). No specific genotype-phenotype correlations were identified. This work confirmed the existence of an attenuated phenotype associated with ATP6V0A2 biallelic variants and offers an updated critique to the clinical and molecular variability of ARCL2A.

Novel TONSL variants cause SPONASTRIME dysplasia and associate with spontaneous chromosome breaks, defective cell proliferation and apoptosis

SPONASTRIME dysplasia is an ultrarare spondyloepimetaphyseal dysplasia featuring short stature and short limbs, platyspondyly, depressed nasal bridge with midface hypoplasia and striated metaphyses. In 2019, an autosomal recessive inheritance was demonstrated by the identification of bi-allelic hypomorphic alleles in TONSL. The encoded protein has a critical role in maintaining genome integrity by promoting the homologous recombination required for repairing spontaneous replication-associated DNA lesions at collapsed replication forks. We report a 9-year-old girl with typical SPONASTRIME dysplasia and resulted in carrier of the novel missense p.(Gln430Arg) and p.(Leu1090Arg) variants in TONSL at whole-exome sequencing. In silico analysis predicted that these variants induced thermodynamic changes with a pathogenic impact on protein function. To support the pathogenicity of the identified variants, cytogenetic analysis and microscopy assays showed that patient-derived fibroblasts exhibited spontaneous chromosomal breaks and flow cytometry demonstrated defects in cell proliferation and enhanced apoptosis. These findings contribute to our understanding of the molecular pathogenesis of SPONASTRIME dysplasia and might open the way to novel therapeutic approaches.

Insights into the molecular pathogenesis of cardiospondylocarpofacial syndrome: MAP3K7 c.737-7A > G variant alters the TGFβ-mediated α-SMA cytoskeleton assembly and autophagy

Transforming growth factor beta-activated kinase 1 (TAK1) is a highly conserved kinase protein encoded by MAP3K7, and activated by multiple extracellular stimuli, growth factors and cytokines. Heterozygous variants in MAP3K7 cause the cardiospondylocarpofacial syndrome (CSCFS) which is characterized by short stature, dysmorphic facial features, cardiac septal defects with valve dysplasia, and skeletal anomalies. CSCFS has been described in seven patients to date and its molecular pathogenesis is only partially understood. Here, the functional effects of the MAP3K7 c.737-7A > G variant, previously identified in a girl with CSCFS and additional soft connective tissue features, were explored. This splice variant generates an in-frame insertion of 2 amino acid residues in the kinase domain of TAK1. Computational analysis revealed that this in-frame insertion alters protein dynamics in the kinase activation loop responsible for TAK1 autophosphorylation after binding with its interactor TAB1. Co-immunoprecipitation studies demonstrate that the ectopic expression of TAK1-mutated protein impairs its ability to physically bind TAB1. In patient's fibroblasts, MAP3K7 c.737-7A > G variant results in reduced TAK1 autophosphorylation and dysregulation of the downstream TAK1-dependent signaling pathway. TAK1 loss-of-function is associated with an impaired TGFβ-mediated α-SMA cytoskeleton assembly and cell migration, and defective autophagy process. These findings contribute to our understanding of the molecular pathogenesis of CSCFS and might offer the rationale for the design of novel therapeutic targets.

Propranolol for familial cerebral cavernous malformation (Treat_CCM): study protocol for a randomized controlled pilot trial

Background

Cerebral cavernous malformations (CCMs) are vascular malformations characterized by clusters of enlarged leaky capillaries in the central nervous system. They may result in intracranial haemorrhage, epileptic seizure(s), or focal neurological deficits, and potentially lead to severe disability. Globally, CCMs represent the second most common intracranial vascular malformation in humans, and their familial form (FCCMs) accounts for one-fifth of cases. Neurosurgical excision, and perhaps stereotactic radiosurgery, is the only available therapeutic option. Case reports suggest that propranolol might modify disease progression.

Methods

Treat_CCM is a prospective, randomized, open-label, blinded endpoint (PROBE), parallel-group trial involving six Italian clinical centres with central reading of brain magnetic resonance imaging (MRI) and adverse events. Patients with symptomatic FCCMs are randomized (2:1 ratio) either to propranolol (40–80 mg twice daily) in addition to standard care or to standard care alone (i.e. anti-epileptic drugs or headache treatments). The primary outcome is intracranial haemorrhage or focal neurological deficit attributable to CCMs. The secondary outcomes are MRI changes over time (i.e. de novo CCM lesions, CCM size and signal characteristics, iron deposition, and vascular leakage as assessed by quantitative susceptibility mapping and dynamic contrast enhanced permeability), disability, health-related quality of life, depression severity, and anxiety (SF-36, BDI-II, State-Trait Anxiety Inventory).

Discussion

Treat_CCM will evaluate the safety and efficacy of propranolol for CCMs following promising case reports in a randomized controlled trial. The direction of effect on the primary outcome and the consistency of effects on the secondary outcomes (even if none of them yield statistically significant differences) of this external pilot study may lead to a larger sample size in a definitive phase 2 trial.

Trial registration

ClinicalTrails.gov, NCT03589014. Retrospectively registered on 17 July 2018.

Mutational spectrum and clinical signatures in 114 families with hereditary multiple osteochondromas: insights into molecular properties of selected exostosin variants

Hereditary multiple osteochondromas (HMO) is a rare autosomal dominant skeletal disorder, caused by heterozygous variants in either EXT1 or EXT2, which encode proteins involved in the biogenesis of heparan sulphate. Pathogenesis and genotype-phenotype correlations remain poorly understood. We studied 114 HMO families (158 affected individuals) with causative EXT1 or EXT2 variants identified by Sanger sequencing, or multiplex ligation-dependent probe amplification and qPCR. Eighty-seven disease-causative variants (55 novel and 32 known) were identified including frameshift (42%), nonsense (32%), missense (11%), splicing (10%) variants and genomic rearrangements (5%). Informative clinical features were available for 42 EXT1 and 27 EXT2 subjects. Osteochondromas were more frequent in EXT1 as compared to EXT2 patients. Anatomical distribution of lesions showed significant differences based on causative gene. Microscopy analysis for selected EXT1 and EXT2 variants verified that EXT1 and EXT2 mutants failed to co-localize each other and loss Golgi localization by surrounding the nucleus and/or assuming a diffuse intracellular distribution. In a cell viability study, cells expressing EXT1 and EXT2 mutants proliferated more slowly than cells expressing wild-type proteins. This confirms the physiological relevance of EXT1 and EXT2 Golgi co-localization and the key role of these proteins in the cell cycle. Taken together, our data expand genotype-phenotype correlations, offer further insights in the pathogenesis of HMO and open the path to future therapies.

TAB2 c.1398dup variant leads to haploinsufficiency and impairs extracellular matrix homeostasis

Transforming growth factor β-activated kinase 1 (TAK1) mediates multiple biological processes through the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) and the mitogen-activated protein kinase (MAPK) signaling pathways. TAK1 activation is tightly regulated by its binding partners (TABs). In particular, binding with TAB2 is crucial for cardiovascular development and extracellular matrix (ECM) homeostasis. In our previous work, we reported a novel multisystem disorder associated with the heterozygous TAB2 c.1398dup variant. Here, we dissect the functional effects of this variant in order to understand its molecular pathogenesis. We demonstrate that TAB2 c.1398dup considerably undergoes to nonsense-mediated messenger RNA decay and encodes a truncated protein that loses its ability to bind TAK1. We also show an alteration of the TAK1 autophosphorylation status and of selected downstream signaling pathways in patients' fibroblasts. Immunofluorescence analyses and ECM-related polymerase chain reaction-array panels highlight that patient fibroblasts display ECM disorganization and altered expression of selected ECM components and collagen-related pathways. In conclusion, we deeply dissect the molecular pathogenesis of the TAB2 c.1398dup variant and show that the resulting phenotype is well explained by TAB2 loss-of-function. Our data also offer initial insights on the ECM homeostasis impairment as a molecular mechanism probably underlying a multisystem disorder linked to TAB2.

Autophagy induction in atrophic muscle cells requires ULK1 activation by TRIM32 through unanchored K63-linked polyubiquitin chains

Optimal autophagic activity is crucial to maintain muscle integrity, with either reduced or excessive levels leading to specific myopathies. LGMD2H is a muscle dystrophy caused by mutations in the ubiquitin ligase TRIM32, whose function in muscles remains not fully understood. Here, we show that TRIM32 is required for the induction of muscle autophagy in atrophic conditions using both in vitro and in vivo mouse models. Trim32 inhibition results in a defective autophagy response to muscle atrophy, associated with increased ROS and MuRF1 levels. The proautophagic function of TRIM32 relies on its ability to bind the autophagy proteins AMBRA1 and ULK1 and stimulate ULK1 activity via unanchored K63-linked polyubiquitin. LGMD2H-causative mutations impair TRIM32's ability to bind ULK1 and induce autophagy. Collectively, our study revealed a role for TRIM32 in the regulation of muscle autophagy in response to atrophic stimuli, uncovering a previously unidentified mechanism by which ubiquitin ligases activate autophagy regulators.