Disruption of the productive encounter complex results in dysregulation of DIAPH1 activity

The diaphanous-related formin, Diaphanous 1 (DIAPH1), is required for the assembly of Filamentous (F)-actin structures. DIAPH1 is an intracellular effector of the receptor for advanced glycation end products (RAGE) and contributes to RAGE signaling and effects such as increased cell migration upon RAGE stimulation. Mutations in DIAPH1, including those in the basic "RRKR" motif of its autoregulatory domain, diaphanous autoinhibitory domain (DAD), are implicated in hearing loss, macrothrombocytopenia, and cardiovascular diseases. The solution structure of the complex between the N-terminal inhibitory domain, DID, and the C-terminal DAD, resolved by NMR spectroscopy shows only transient interactions between DID and the basic motif of DAD, resembling those found in encounter complexes. Cross-linking studies placed the RRKR motif into the negatively charged cavity of DID. Neutralizing the cavity resulted in a 5-fold decrease in the binding affinity and 4-fold decrease in the association rate constant of DAD for DID, indicating that the RRKR interactions with DID form a productive encounter complex. A DIAPH1 mutant containing a neutralized RRKR binding cavity shows excessive colocalization with actin and is unresponsive to RAGE stimulation. This is the first demonstration of a specific alteration of the surfaces responsible for productive encounter complexation with implications for human pathology.

An Extended Iranian Family with Autosomal Dominant Non-syndromic Hearing Loss Associated with A Nonsense Mutation in the DIAPH1 Gene

Genetic analysis of non-syndromic hearing loss (NSHL) has been challenged due to marked clinical and genetic heterogeneity. Today, advanced next-generation sequencing (NGS) technologies, such as exome sequencing (ES), have drastically increased the efficacy of gene identification in heterogeneous Mendelian disorders. Here, we present the utility of ES and re-evaluate the phenotypic data for identifying candidate causal variants for previously unexplained progressive moderate to severe NSHL in an extended Iranian family. Using this method, we identified a known heterozygous nonsense variant in exon 26 of the DIAPH1 gene (MIM: 602121), which led to "Deafness, autosomal dominant 1, with or without thrombocytopenia; DFNA1" (MIM: 124900) in this large family in the absence of GJB2 disease-causing variants and also OtoSCOPE-negative results. To the best of our knowledge, this nonsense variant (NM_001079812.3):c.3610C>T (p.Arg1204Ter) is the first report of the DIAPH1 gene variant for autosomal dominant non-syndromic hearing loss (ADNSHL) in Iran.

Formin protein DIAPH1 positively regulates PD-L1 expression and predicts the therapeutic response to anti-PD-1/PD-L1 immunotherapy

Formins are evolutionarily conserved genes and profoundly affect cancer progression. This study aims to explore the expressions, prognostic values, and immunological correlations of Formins in cancer. Specific Formins were dysregulated and immuno-biologically correlated in breast cancer (BRCA). Formins showed different expression patterns, namely some were enriched in immune cells while some were enriched in tumor cells. Among all Formins, DIAPH1 was enriched in tumor cells and associated with an inflamed tumor microenvironment (TME). DIAPH1 functioned as an oncogene in BRCA and mediated TGF-β1-induced epithelial-mesenchymal transformation (EMT) and PD-L1 expression. Moreover, DIAPH1 was overexpressed in most cancers and functioned as a novel pan-cancer immuno-marker, which could predict the response to anti-PD-1/PD-L1 immunotherapy. Overall, DIAPH1 functions as an oncogene and is immunologically correlated, which could be utilized as an alternative biomarker for predicting the immunotherapeutic response.

Diaphanous-related formin subfamily: Novel prognostic biomarkers and tumor microenvironment regulators for pancreatic adenocarcinoma

The diaphanous-related formin subfamily includes diaphanous homolog 1 (DIAPH1), DIAPH2, and DIAPH3. DIAPHs play a role in the regulation of actin nucleation and polymerization and in microtubule stability. DIAPH3 also regulates the assembly and bipolarity of mitotic spindles. Accumulating evidence has shown that DIAPHs are anomalously regulated during malignancy. In this study, we reviewed The Cancer Genome Atlas database and found that DIAPHs are abundantly expressed in pancreatic adenocarcinoma (PAAD). Furthermore, we analyzed the gene alteration profiles, protein expression, prognosis, and immune reactivity of DIAPHs in PAAD using data from several well-established databases. In addition, we conducted gene set enrichment analysis to investigate the potential mechanisms underlying the roles of DIAPHs in the carcinogenesis of PAAD. Finally, we performed the experimental validation of DIAPHs expression in several pancreatic cancer cell lines and tissues of patients. This study demonstrated significant correlations between DIAPHs expression and clinical prognosis, oncogenic signature gene sets, T helper 2 cell infiltration, plasmacytoid dendritic cell infiltration, myeloid-derived suppressor cell infiltration, ImmunoScore, and immune checkpoints in PAAD. These data may provide important information regarding the role and mechanisms of DIAPHs in tumorigenesis and PAAD immunotherapy.

Circ_0044556 Promotes the Progression of Colorectal Cancer via the miR-665-Dependent Expression Regulation of Diaphanous Homolog 1

BACKGROUND

Cancer progression can be regulated by noncoding circular RNAs. A recent study has indicated that circ_0044556 facilitated the progression of colorectal cancer.

AIM

This research was performed to explore the regulatory mechanism of circ_0044556 in CRC.

METHODS

Circ_0044556, miR-665 and Diaphanous Homolog 1 levels were detected by the quantitative real-time polymerase chain reaction. Cell proliferation analysis was performed by cell counting kit-8 assay and Edu assay. Cell cycle progression was assessed using flow cytometry. The protein examination was conducted using western blot. Transwell assay was used to analyze cell migration and invasion. Dual-luciferase reporter assay was performed to validate the interaction between targets. In vivo research was implemented by xenograft tumor assay.

RESULTS

Circ_0044556 was upregulated in colorectal cancer samples and cells. Silencing circ_0044556 inhibited cell proliferation, cell cycle progression, migration, invasion, and epithelial-mesenchymal transition in CRC cells. Circ_0044556 could directly target miR-665 and the function of circ_0044556 was associated with the regulation of miR-665. In addition, Diaphanous Homolog 1 was a target gene for miR-665 and the anti-tumor role of miR-665 in colorectal cancer was dependent on the downregulation of Diaphanous Homolog 1. Diaphanous Homolog 1 level was regulated by circ_0044556 via sponging miR-665 in CRC cells. In vivo assay suggested that circ_0044556 promoted CRC tumor growth by regulating the miR-665 and Diaphanous Homolog 1 levels.

CONCLUSION

Our findings manifested that circ_0044556 functioned as an oncogenic circRNA in colorectal cancer by mediating the miR-665/Diaphanous Homolog 1 axis, elucidating the molecular mechanism of circ_0044556 in CRC progression.

Role of Cytoskeletal Diaphanous-Related Formins in Hearing Loss

Hearing relies on the proper functioning of auditory hair cells and on actin-based cytoskeletal structures. Diaphanous-related formins (DRFs) are evolutionarily conserved cytoskeletal proteins that regulate the nucleation of linear unbranched actin filaments. They play key roles during metazoan development, and they seem particularly pivotal for the correct physiology of the reproductive and auditory systems. Indeed, in Drosophila melanogaster, a single diaphanous (dia) gene is present, and mutants show sterility and impaired response to sound. Vertebrates, instead, have three orthologs of the diaphanous gene: DIAPH1, DIAPH2, and DIAPH3. In humans, defects in DIAPH1 and DIAPH3 have been associated with different types of hearing loss. In particular, heterozygous mutations in DIAPH1 are responsible for autosomal dominant deafness with or without thrombocytopenia (DFNA1, MIM #124900), whereas regulatory mutations inducing the overexpression of DIAPH3 cause autosomal dominant auditory neuropathy 1 (AUNA1, MIM #609129). Here, we provide an overview of the expression and function of DRFs in normal hearing and deafness.

The RAGE/DIAPH1 Signaling Axis & Implications for the Pathogenesis of Diabetic Complications

Increasing evidence links the RAGE (receptor for advanced glycation end products)/DIAPH1 (Diaphanous 1) signaling axis to the pathogenesis of diabetic complications. RAGE is a multi-ligand receptor and through these ligand-receptor interactions, extensive maladaptive effects are exerted on cell types and tissues targeted for dysfunction in hyperglycemia observed in both type 1 and type 2 diabetes. Recent evidence indicates that RAGE ligands, acting as damage-associated molecular patterns molecules, or DAMPs, through RAGE may impact interferon signaling pathways, specifically through upregulation of IRF7 (interferon regulatory factor 7), thereby heralding and evoking pro-inflammatory effects on vulnerable tissues. Although successful targeting of RAGE in the clinical milieu has, to date, not been met with success, recent approaches to target RAGE intracellular signaling may hold promise to fill this critical gap. This review focuses on recent examples of highlights and updates to the pathobiology of RAGE and DIAPH1 in diabetic complications.

Fibrogenic signals persist in DAA-treated HCV patients after sustained virological response

BACKGROUND & AIMS

Patients with HCV who achieve a sustained virological response (SVR) on direct-acting antiviral (DAA) therapy still need to be monitored for signs of liver disease progression. To this end, the identification of both disease biomarkers and therapeutic targets is necessary.

METHODS

Extracellular vesicles (EVs) purified from plasma of 15 healthy donors (HDs), and 16 HCV-infected patients before (T0) and after (T6) DAA treatment were utilized for functional and miRNA cargo analysis. EVs purified from plasma of 17 HDs and 23 HCV-infected patients (T0 and T6) were employed for proteomic and western blot analyses. Functional analysis in LX2 cells measured fibrotic markers (mRNAs and proteins) in response to EVs. Structural analysis was performed by qPCR, label-free liquid chromatography-mass spectrometry and western blot.

RESULTS

On the basis of observations indicating functional differences (i.e. modulation of FN-1, ACTA2, Smad2/3 phosphorylation, collagen deposition) of plasma-derived EVs from HDs, T0 and T6, we performed structural analysis of EVs. We found consistent differences in terms of both miRNA and protein cargos: (i) antifibrogenic miR204-5p, miR181a-5p, miR143-3p, miR93-5p and miR122-5p were statistically underrepresented in T0 EVs compared to HD EVs, while miR204-5p and miR143-3p were statistically underrepresented in T6 EVs compared to HD EVs (p <0.05); (ii) proteomic analysis highlighted, in both T0 and T6, the modulation of several proteins with respect to HDs; among them, the fibrogenic protein DIAPH1 was upregulated (Log₂ fold change of 4.4).

CONCLUSIONS

Taken together, these results highlight structural EV modifications that are conceivably causal for long-term liver disease progression in patients with HCV despite DAA-mediated SVR.

LAY SUMMARY

Direct-acting antivirals lead to virological cure in the majority of patients with chronic hepatitis C virus infection. However, the risk of liver disease progression or complications in patients with fibrosis and cirrhosis remains in some patients even after virological cure. Herein, we show that extracellular vesicle modifications could be linked to long-term liver disease progression in patients who have achieved virological cure; these modifications could potentially be used as biomarkers or treatment targets in such patients.

DIAPH1 Promotes Laryngeal Squamous Cell Carcinoma Progression Through Cell Cycle Regulation

The diaphanous related formin 1 (DIAPH1) protein is involved in the regulation of dynamic cytoskeleton reorganization, which is closely related to mitosis and the cell cycle. Cell cycle disorders are generally regarded as important underlying causes of many cancers. In the current study, we have revealed that DIAPH1 expression is an independent prognostic factor for overall survival in patients with laryngeal squamous cell carcinoma (LSCC) and that DIAPH1 promotes colony formation, cell proliferation, and G1/S progression in LSCC cells. Additionally, DIAPH1 promotes growth of AMC-HN-8 LSCC-derived tumors in vivo. In this study, RNA-sequencing analysis revealed that DIAPH1 knockdown led to changes in the expression of genes associated with signaling during the cell cycle. Using western blot analyses, we further demonstrated that DIAPH1 knockdown resulted in upregulation of p21^Waf1/Cip1, p19^Ink4d, p27^Kip1, and p16^Ink4a and downregulation of cyclinA2, cyclinD1, CDK2, CDK4, and CDK6. These results suggest that DIAPH1 influences the expression of genes in several signaling pathways and promotes LSCC progression by regulating the cell cycle.

The cross-talk between RAGE and DIAPH1 in neurological complications of diabetes: A review

Neuropathy, or dysfunction of peripheral nerve, is one of the most common neurological manifestation in patients with diabetes mellitus (DM). DM is typically associated with a hyperglycaemic milieu, which promotes non-enzymatic glycation of proteins. Proteins with advanced glycation are known to engage a cell-surface receptor called the receptor for advanced glycation end products (RAGE). Thus, it is reasonable to assume that RAGE and its associated molecule-mediated cellular signalling may contribute to DM-induced symmetrical axonal (length-dependent) neuropathy. Of particular interest is diaphanous related formin 1 (DIAPH1), a cytoskeletal organizing molecule, which interacts with the cytosolic domain of RAGE and whose dysfunction may precipitate axonopathy/neuropathy. Indeed, it has been demonstrated that both RAGE and DIAPH1 are expressed in the motor and sensory fibres of nerve harvested from DM animal models. Although the detailed molecular role of RAGE and DIAPH1 in diabetic neurological complications remains unclear, here we will discuss available evidence of their involvement in peripheral diabetic neuropathy. Specifically, we will discuss how a hyperglycaemic environment is not only likely to elevate advanced glycation end products (ligands of RAGE) and induce a pro-inflammatory environment but also alter signalling via RAGE and DIAPH1. Further, hyperglycaemia may regulate epigenetic mechanisms that interacts with RAGE signalling. We suggest the cumulative effect of hyperglycaemia on RAGE-DIAPH1-mediated signalling may be disruptive to axonal cytoskeletal organization and transport and is therefore likely to play a key role in pathogenesis of diabetic symmetrical axonal neuropathy.

Building platelet phenotypes: diaphanous-related formin 1 (DIAPH1)-related disorder

Variants of the Diaphanous-Related Formin 1 (DIAPH-1) gene have recently been reported causing inherited macrothrombocytopenia. The essential/"diagnostic" characteristics associated with the disorder are emerging; however, robust and complete criteria are not established. Here, we report the first cases of DIAPH1-related disorder in Australia caused by the autosomal dominant gain-of-function DIAPH1 R1213X variant formed by truncation of the protein within the diaphanous auto-regulatory domain (DAD) with loss of regulatory motifs responsible for autoinhibitory interactions within the DIAPH1 protein. We affirm phenotypic changes induced by the DIAPH1 R1213X variant to include macrothrombocytopenia, early-onset progressive sensorineural hearing loss, and mild asymptomatic neutropenia. High-resolution microscopy confirms perturbations of cytoskeletal dynamics caused by the DIAPH1 variant and we extend the repertoire of changes generated by this variant to include alteration of procoagulant platelet formation and possible dental anomalies.

Loss of DIAPH1 causes SCBMS, combined immunodeficiency, and mitochondrial dysfunction

BACKGROUND

Homozygous loss of DIAPH1 results in seizures, cortical blindness, and microcephaly syndrome (SCBMS). We studied 5 Finnish and 2 Omani patients with loss of DIAPH1 presenting with SCBMS, mitochondrial dysfunction, and immunodeficiency.

OBJECTIVE

We sought to further characterize phenotypes and disease mechanisms associated with loss of DIAPH1.

METHODS

Exome sequencing, genotyping and haplotype analysis, B- and T-cell phenotyping, in vitro lymphocyte stimulation assays, analyses of mitochondrial function, immunofluorescence staining for cytoskeletal proteins and mitochondria, and CRISPR-Cas9 DIAPH1 knockout in heathy donor PBMCs were used.

RESULTS

Genetic analyses found all Finnish patients homozygous for a rare DIAPH1 splice-variant (NM_005219:c.684+1G>A) enriched in the Finnish population, and Omani patients homozygous for a previously described pathogenic DIAPH1 frameshift-variant (NM_005219:c.2769delT;p.F923fs). In addition to microcephaly, epilepsy, and cortical blindness characteristic to SCBMS, the patients presented with infection susceptibility due to defective lymphocyte maturation and 3 patients developed B-cell lymphoma. Patients' immunophenotype was characterized by poor lymphocyte activation and proliferation, defective B-cell maturation, and lack of naive T cells. CRISPR-Cas9 knockout of DIAPH1 in PBMCs from healthy donors replicated the T-cell activation defect. Patient-derived peripheral blood T cells exhibited impaired adhesion and inefficient microtubule-organizing center repositioning to the immunologic synapse. The clinical symptoms and laboratory tests also suggested mitochondrial dysfunction. Experiments with immortalized, patient-derived fibroblasts indicated that DIAPH1 affects the amount of complex IV of the mitochondrial respiratory chain.

CONCLUSIONS

Our data demonstrate that individuals with SCBMS can have combined immune deficiency and implicate defective cytoskeletal organization and mitochondrial dysfunction in SCBMS pathogenesis.

DIAPH1 Mutation as a Novel Cause of Autosomal Dominant Macrothrombocytopenia and Hearing Loss

Macrothrombocytopenia (MTP) is a group of rare disorders characterized by giant platelets, thrombocytopenia, and variable association with abnormal bleeding. Inherited MTP are frequently misdiagnosed as immune thrombocytopenia. Associated second-organ manifestation can help narrow down syndromic MTPs. We describe a case of autosomal dominant sensorineural hearing loss and MTP caused by a gain of function mutation in DIAPH1. This mutation causes altered megarkaryopoiesis and platelet cytoskeletal deregulation. Although hearing loss and MTP were likely progressive, clinically significant bleeding was not observed. DIAPH1-related MTP can be distinguished clinically from MYH9 mutation by the absence of cataracts and glomerular disease.

A novel variant in diaphanous homolog 1 (DIAPH1) as the cause of auditory neuropathy in a Chinese family

OBJECTIVES

To determine the genetic cause of non-syndromic autosomal dominant deafness segregating in a Chinese Auditory neuropathy (AN) family.

INTRODUCTION

AN is a genetically related rare disease characterized by sensorineural hearing loss and retention of hair cell function. Diaphanous Homolog 1 (DIAPH1) is the causative gene of DFNA1. To date, no evidence has been detected to reveal the connection between gene DIAPH1 and AN.

MATERIAL AND METHODS

Audiological and imageological examinations, genome-wide linkage analysis, and whole exome sequencing (WES) were carried out on the family members.

RESULTS

In the 13-member branch of the family, 4 patients with preserved otoacoustic emission or cochlear microphonic and abnormal auditory brainstem responses were diagnosed with AN. Linkage analysis detected an interval with a LOD (log odds) score >4 on chr5:138.845-149.509 cM. Using WES we identified a novel frameshift variant c.3551_3552del (p.Glu1184AlafsTer11) in exon 26 of DIAPH1 located in the linkage region. The variant was co-segregated with hearing impairment phenotype in the family except 4 members below the average age of onset. We have found sufficient evidence conforming with the American College of Medical Genetics and Genomics Guideline to consider c.3551_3552del as the genetic cause of the family patients.

CONCLUSION

It is the first report to expand DIAPH1-related phenotypic spectrum to include AN. Our findings could facilitate the clinical diagnosis and genetic counselling for AN, especially for those with DIAPH1 variants.

CREB1-induced lncRNA LEF1-AS1 contributes to colorectal cancer progression via the miR-489/DIAPH1 axis

Long non-coding RNAs (lncRNAs) have been identified as new regulatory factors in tumor progression. Lymphoid enhancer-binding factor 1 antisense RNA 1 (LEF1-AS1) was a recently identified lncRNA. This research aimed to investigate the roles and mechanisms of LEF1-AS1 in colorectal cancer (CRC). We firstly showed that LEF1-AS1 expression was upregulated in human CRC tissues and cell lines. LEF1-AS1 upregulation was demonstrated to be induced by CREB1. Clinical study revealed that high LEF1-AS1 expression was positively associated with histological grade, lymph nodes metastasis, and decreased survivals of CRC patients. Functionally, down-regulation of LEF1-AS1 using si-LEF1-AS1 decreased cell growth, migration and invasion, as well as increased apoptosis in CRC cells. Mechanically, LEF1-AS1 functioned as competing endogenous RNA (ceRNA) for miR-489 to positively recover DIAPH1, thus playing an oncogenic role in CRC pathogenesis. Overall, our observations identified a novel CRC-related lncRNA LEF1-AS1 and discovered a critical role for this lncRNA as a ceRNA in CRC pathogenesis, suggesting that it may serve as a novel biomarker for prognosis and act as a therapeutic target for CRC treatment.

Receptor for Advanced Glycation End Products (RAGE) and Mechanisms and Therapeutic Opportunities in Diabetes and Cardiovascular Disease: Insights From Human Subjects and Animal Models

Obesity and diabetes are leading causes of cardiovascular morbidity and mortality. Although extensive strides have been made in the treatments for non-diabetic atherosclerosis and its complications, for patients with diabetes, these therapies provide less benefit for protection from cardiovascular disease (CVD). These considerations spur the concept that diabetes-specific, disease-modifying therapies are essential to identify, especially as the epidemics of obesity and diabetes continue to expand. Hence, as hyperglycemia is a defining feature of diabetes, it is logical to probe the impact of the specific consequences of hyperglycemia on the vessel wall, immune cell perturbation, and endothelial dysfunction-all harbingers to the development of CVD. In this context, high levels of blood glucose stimulate the formation of the irreversible advanced glycation end products, the products of non-enzymatic glycation and oxidation of proteins and lipids. AGEs accumulate in diabetic circulation and tissues and the interaction of AGEs with their chief cellular receptor, receptor for AGE or RAGE, contributes to vascular and immune cell perturbation. The cytoplasmic domain of RAGE lacks endogenous kinase activity; the discovery that this intracellular domain of RAGE binds to the formin, DIAPH1, and that DIAPH1 is essential for RAGE ligand-mediated signal transduction, identifies the specific cellular means by which RAGE functions and highlights a new target for therapeutic interruption of RAGE signaling. In human subjects, prominent signals for RAGE activity include the presence and levels of two forms of soluble RAGE, sRAGE, and endogenous secretory (es) RAGE. Further, genetic studies have revealed single nucleotide polymorphisms (SNPs) of the AGER gene (AGER is the gene encoding RAGE) and DIAPH1, which display associations with CVD. This Review presents current knowledge regarding the roles for RAGE and DIAPH1 in the causes and consequences of diabetes, from obesity to CVD. Studies both from human subjects and animal models are presented to highlight the breadth of evidence linking RAGE and DIAPH1 to the cardiovascular consequences of these metabolic disorders.

Association of DIAPH1 gene polymorphisms with ischemic stroke

DIAPH1 is a formin protein involved in actin polymerization with important roles in vascular remodeling and thrombosis. To investigate potential associations of DIAPH1 single-nucleotide polymorphisms (SNPs) with hypertension and stroke, 2,012 patients with hypertension and 2,210 controls, 2,966 stroke cases [2,212 ischemic stroke (IS), 754 hemorrhagic stroke (HS)] and 2,590 controls were enrolled respectively in the case-control study. A total of 4,098 individual were included in the cohort study. DIAPH1 mRNA expression was compared between 66 IS [43 small artery occlusion (SAO) and 23 large-artery atherosclerosis (LAA)] and 58 controls. Odds ratio (OR), hazard ratio (HR) and 95% confidence interval (CI) were calculated by logistic and cox regression analysis. Rs7703688 T>C variation was significantly associated with an increased risk of IS [OR (95% CI) was 1.721 (1.486-1.993), P=4.139×10^-12]. Association of rs7703688 with stroke risk was further validated in the cohort study [adjusted HRs (95% CIs) for additive and recessive models were 1.385 (1.001-1.918), P=0.049, and 2.882 (1.038-8.004), P=0.042, respectively)]. DIAPH1 mRNA expression was significantly downregulated in IS. In SAO stroke subtype, DIAPH1 expression has an increased trend among rs251019 genotypes (P_trend=0.048). These novel findings suggest that DIAPH1 variation contributes to genetic susceptibility to stroke risk, especially the SAO subtype of IS.

Formin-like 1 (FMNL1) Is Associated with Glioblastoma Multiforme Mesenchymal Subtype and Independently Predicts Poor Prognosis

Glioblastoma multiforme (GBM), the most common primary malignant brain tumor in adults, is characterized by rapid proliferation, aggressive migration, and invasion into normal brain tissue. Formin proteins have been implicated in these processes. However, the role of formin-like 1 (FMNL1) in cancer remains unclear. We studied FMNL1 expression in glioblastoma samples using immunohistochemistry. We sought to analyze the correlation between FMNL1 expression, clinicopathologic variables, and patient survival. Migration and invasion assays were used to verify the effect of FMNL1 on glioblastoma cell lines. Microarray data were downloaded from The Cancer Genome Atlas and analyzed using gene set enrichment analysis (GSEA). FMNL1 was an independent predictor of poor prognosis in a cohort of 217 glioblastoma multiforme cases (p < 0.001). FMNL1 expression was significantly higher in the mesenchymal subtype. FMNL1 upregulation and downregulation were associated with mesenchymal and proneural markers in the GSEA, respectively. These data highlight the important role of FMNL1 in the neural-to-mesenchymal transition. Conversely, FMNL1 downregulation suppressed glioblastoma multiforme cell migration and invasion via DIAPH1 and GOLGA2, respectively. FMNL1 downregulation also suppressed actin fiber assembly, induced morphological changes, and diminished filamentous actin. FMNL1 is a promising therapeutic target and a useful biomarker for GBM progression.

Diaphanous 1 (DIAPH1) is Highly Expressed in the Aged Human Medial Temporal Cortex and Upregulated in Myeloid Cells During Alzheimer's Disease

BACKGROUND

The receptor for advanced glycation end products (RAGE) is linked to cellular stress and inflammation during Alzheimer's disease (AD). RAGE signals through Diaphanous-1 (DIAPH1); however, the expression of DIAPH1 in the healthy and AD human brain has yet to be methodically addressed.

OBJECTIVE

To delineate the cell- and disease-state specific expression of DIAPH1 in the human medial temporal cortex during healthy aging and AD.

METHODS

We used semi-quantitative immunohistochemistry in the human medial temporal cortex paired with widefield and confocal microscopy and automated analyses to determine colocalization and relative expression of DIAPH1 with key cell markers and molecules in the brains of subjects with AD versus age-matched controls.

RESULTS

We report robust colocalization of DIAPH1 with myeloid cells and increased expression during AD, which strongly correlated to increased neutral lipids and morphology of inflamed myeloid cells. DIAPH1 moderately colocalized with markers of endothelial cells, astrocytes, neurons, and oligodendrocytes.

DISCUSSION

Our findings localize DIAPH1 particularly to myeloid cells in the CNS, especially in AD in the locations of lipid droplet accumulation, thereby implicating RAGE-DIAPH1 signaling in dysregulated lipid metabolism and morphological changes of inflamed myeloid cells in this disorder.

Deletion of the formin Diaph1 protects from structural and functional abnormalities in the murine diabetic kidney

Diaphanous 1 (DIAPH1), a member of the formin family, binds to the cytoplasmic domain of the receptor for advanced glycation end products (RAGE) and is required for RAGE signal transduction. Experiments employing genetic overexpression or deletion of Ager (the gene encoding RAGE) or its pharmacological antagonism implicate RAGE in the pathogenesis of diabetes-associated nephropathy. We hypothesized that DIAPH1 contributes to pathological and functional derangements in the kidneys of diabetic mice. We show that DIAPH1 is expressed in the human and murine diabetic kidney, at least in part in the tubulointerstitium and glomerular epithelial cells or podocytes. To test the premise that DIAPH1 is linked to diabetes-associated derangements in the kidney, we rendered male mice globally devoid of Diaph1 ( Diaph1^-/-) or wild-type controls (C57BL/6 background) diabetic with streptozotocin. Control mice received equal volumes of citrate buffer. After 6 mo of hyperglycemia, diabetic Diaph1^-/- mice displayed significantly reduced mesangial sclerosis, podocyte effacement, glomerular basement thickening, and urinary albumin-to-creatinine ratio compared with diabetic mice expressing Diaph1. Analysis of whole kidney cortex revealed that deletion of Diaph1 in diabetic mice significantly reduced expression of genes linked to fibrosis and inflammation. In glomerular isolates, expression of two genes linked to podocyte stress, growth arrest-specific 1 ( Gas1) and cluster of differentiation 36 ( Cd36), was significantly attenuated in diabetic Diaph1^-/- mice compared with controls, in parallel with significantly higher levels of nestin (Nes) mRNA, a podocyte marker. Collectively, these data implicate DIAPH1 in the pathogenesis of diabetes-associated nephropathy and suggest that the RAGE-DIAPH1 axis is a logical target for therapeutic intervention in this disorder.

The Formin, DIAPH1, is a Key Modulator of Myocardial Ischemia/Reperfusion Injury

The biochemical, ionic, and signaling changes that occur within cardiomyocytes subjected to ischemia are exacerbated by reperfusion; however, the precise mechanisms mediating myocardial ischemia/reperfusion (I/R) injury have not been fully elucidated. The receptor for advanced glycation end-products (RAGE) regulates the cellular response to cardiac tissue damage in I/R, an effect potentially mediated by the binding of the RAGE cytoplasmic domain to the diaphanous-related formin, DIAPH1. The aim of this study was to investigate the role of DIAPH1 in the physiological response to experimental myocardial I/R in mice. After subjecting wild-type mice to experimental I/R, myocardial DIAPH1 expression was increased, an effect that was echoed following hypoxia/reoxygenation (H/R) in H9C2 and AC16 cells. Further, compared to wild-type mice, genetic deletion of Diaph1 reduced infarct size and improved contractile function after I/R. Silencing Diaph1 in H9C2 cells subjected to H/R downregulated actin polymerization and serum response factor-regulated gene expression. Importantly, these changes led to increased expression of sarcoplasmic reticulum Ca2+ ATPase and reduced expression of the sodium calcium exchanger. This work demonstrates that DIAPH1 is required for the myocardial response to I/R, and that targeting DIAPH1 may represent an adjunctive approach for myocardial salvage after acute infarction.

Glycation & the RAGE axis: targeting signal transduction through DIAPH1

INTRODUCTION

The consequences of chronic disease are vast and unremitting; hence, understanding the pathogenic mechanisms mediating such disorders holds promise to identify therapeutics and diminish the consequences. The ligands of the receptor for advanced glycation end products (RAGE) accumulate in chronic diseases, particularly those characterized by inflammation and metabolic dysfunction. Although first discovered and reported as a receptor for advanced glycation end products (AGEs), the expansion of the repertoire of RAGE ligands implicates the receptor in diverse milieus, such as autoimmunity, chronic inflammation, obesity, diabetes, and neurodegeneration. Areas covered: This review summarizes current knowledge regarding the ligand families of RAGE and data from human subjects and animal models on the role of the RAGE axis in chronic diseases. The recent discovery that the cytoplasmic domain of RAGE binds to the formin homology 1 (FH1) domain, DIAPH1, and that this interaction is essential for RAGE ligand-stimulated signal transduction, is discussed. Finally, we review therapeutic opportunities targeting the RAGE axis as a means to mitigate chronic diseases. Expert commentary: With the aging of the population and the epidemic of cardiometabolic disease, therapeutic strategies to target molecular pathways that contribute to the sequelae of these chronic diseases are urgently needed. In this review, we propose that the ligand/RAGE axis and its signaling nexus is a key factor in the pathogenesis of chronic disease and that therapeutic interruption of this pathway may improve quality and duration of life.

Constitutive activation of DIA1 (DIAPH1) via C-terminal truncation causes human sensorineural hearing loss

DIAPH1 encodes human DIA1, a formin protein that elongates unbranched actin. The c.3634+1G>T DIAPH1 mutation causes autosomal dominant nonsyndromic sensorineural hearing loss, DFNA1, characterized by progressive deafness starting in childhood. The mutation occurs near the C‐terminus of the diaphanous autoregulatory domain (DAD) of DIA1, which interacts with its N‐terminal diaphanous inhibitory domain (DID), and may engender constitutive activation of DIA1. However, the underlying pathogenesis that causes DFNA1 is unclear. We describe a novel patient‐derived DIAPH1 mutation (c.3610C>T) in two unrelated families, which results in early termination prior to a basic amino acid motif (RRKR^1204–1207) at the DAD C‐terminus. The mutant DIA1(R1204X) disrupted the autoinhibitory DID‐DAD interaction and was constitutively active. This unscheduled activity caused increased rates of directional actin polymerization movement and induced formation of elongated microvilli. Mice expressing FLAG‐tagged DIA1(R1204X) experienced progressive deafness and hair cell loss at the basal turn and had various morphological abnormalities in stereocilia (short, fused, elongated, sparse). Thus, the basic region of the DAD mediates DIA1 autoinhibition; disruption of the DID‐DAD interaction and consequent activation of DIA1(R1204X) causes DFNA1.

Novel loss-of-function variants in DIAPH1 associated with syndromic microcephaly, blindness, and early onset seizures

Exome sequencing identified homozygous loss-of-function variants in DIAPH1 (c.2769delT; p.F923fs and c.3145C>T; p.R1049X) in four affected individuals from two unrelated consanguineous families. The affected individuals in our report were diagnosed with postnatal microcephaly, early-onset epilepsy, severe vision impairment, and pulmonary symptoms including bronchiectasis and recurrent respiratory infections. A heterozygous DIAPH1 mutation was originally reported in one family with autosomal dominant deafness. Recently, however, a homozygous nonsense DIAPH1 mutation (c.2332C4T; p.Q778X) was reported in five siblings in a single family affected by microcephaly, blindness, early onset seizures, developmental delay, and bronchiectasis. The role of DIAPH1 was supported using parametric linkage analysis, RNA and protein studies in their patients' cell lines and further studies in human neural progenitors cells and a diap1 knockout mouse. In this report, the proband was initially brought to medical attention for profound metopic synostosis. Additional concerns arose when his head circumference did not increase after surgical release at 5 months of age and he was diagnosed with microcephaly and epilepsy at 6 months of age. Clinical exome analysis identified a homozygous DIAPH1 mutation. Another homozygous DIAPH1 mutation was identified in the research exome analysis of a second family with three siblings presenting with a similar phenotype. Importantly, no hearing impairment is reported in the homozygous affected individuals or in the heterozygous carrier parents in any of the families demonstrating the autosomal recessive microcephaly phenotype. These additional families provide further evidence of the likely causal relationship between DIAPH1 mutations and a neurodevelopmental disorder.