Elucidation of subfamily segregation and intramolecular coevolution of the olfactomedin-like proteins by comprehensive phylogenetic analysis and gene expression pattern assessment

Identification of OPTN p.(Asn51Thr): A novel pathogenic variant in primary open-angle glaucoma

Purpose

Pathogenic variants in TBK1, MYOC, and OPTN are associated with primary open-angle glaucoma (POAG) with severe visual field defects. This study aims to understand further POAG-related pathogenic variant(s) based on a cohort of East Asian populations that have not been well-characterized.

Methods

We conducted a comprehensive screening of TBK1, MYOC, and OPTN variants in 174 POAG Japanese patients, followed by 8380 population-specific genome sequencing data references, segregation analysis, and functional protein assays to determine pathogenic variants.

Results

Despite the small sample size, 4 variants were novel, 2 of which p.(Cys5Trp) and p.(Thr293Met) were in the MYOC gene, and 2 p.(Asn51Thr), and p.(Gln142His) were in the OPTN. Notably, the OPTN p.(Asn51Thr) missense variant adjacent to the p.(Glu50Lys) variant, a well-known POAG pathogenic variant, was segregated from all proband's family members with POAG. Moreover, in silico and in vitro analyses revealed that the OPTN p.(Asn51Thr) protein increased binding instability, interactions of the OPTN-TBK1 complex, and enhanced protein insolubility, likewise the p.(Glu50Lys) protein.

Conclusion

Our findings may provide further genetic insights into rare variants of POAG and support the clear conclusion that OPTN p.(Asn51Thr) is a novel likely pathogenic variant.

Myocilin misfolding and glaucoma: A 20-year update

Mutations in the gene MYOC account for approximately 5% of cases of primary open angle glaucoma (POAG). MYOC encodes for the protein myocilin, a multimeric secreted glycoprotein composed of N-terminal coiled-coil (CC) and leucine zipper (LZ) domains that are connected via a disordered linker to a 30 kDa olfactomedin (OLF) domain. More than 90% of glaucoma-causing mutations are localized to the OLF domain. While myocilin is expressed in numerous tissues, mutant myocilin is only associated with disease in the anterior segment of the eye, in the trabecular meshwork. The prevailing pathogenic mechanism involves a gain of toxic function whereby mutant myocilin aggregates intracellularly instead of being secreted, which causes cell stress and an early timeline for TM cell death, elevated intraocular pressure, and subsequent glaucoma-associated retinal degeneration. In this review, we focus on the work our lab has conducted over the past ∼15 years to enhance our molecular understanding of myocilin-associated glaucoma, which includes details of the molecular structure and the nature of the aggregates formed by mutant myocilin. We conclude by discussing open questions, such as predicting phenotype from genotype alone, the elusive native function of myocilin, and translational directions enabled by our work.

Obesity wars: may the smell be with you

Classically, the regulation of energy balance has been based on central and peripheral mechanisms sensing energy, nutrients, metabolites, and hormonal cues. Several cellular mechanisms at central level, such as hypothalamic AMP-activated protein kinase (AMPK), integrate this information to elicit counterregulatory responses that control feeding, energy expenditure, and glucose homeostasis, among other processes. Recent data have added more complexity to the homeostatic regulation of metabolism by introducing, for example, the key role of "traditional" senses and sensorial information in this complicated network. In this regard, current evidence is showing that olfaction plays a key and bidirectional role in energy homeostasis. Although nutritional status dynamically and profoundly impacts olfactory sensitivity, the sense of smell is involved in food appreciation and selection, as well as in brown adipose tissue (BAT) thermogenesis and substrate utilization, with some newly described actors, such as olfactomedin 2 (OLFM2), likely playing a major role. Thus, olfactory inputs are contributing to the regulation of both sides of the energy balance equation, namely, feeding and energy expenditure (EE), as well as whole body metabolism. Here, we will review the current knowledge and advances about the role of olfaction in the regulation of energy homeostasis.

Brain compartmentalization based on transcriptome analyses and its gene expression in Octopus minor

Coleoid cephalopods have a high intelligence, complex structures, and large brain. The cephalopod brain is divided into supraesophageal mass, subesophageal mass and optic lobe. Although much is known about the structural organization and connections of various lobes of octopus brain, there are few studies on the brain of cephalopod at the molecular level. In this study, we demonstrated the structure of an adult Octopus minor brain by histomorphological analyses. Through visualization of neuronal and proliferation markers, we found that adult neurogenesis occurred in the vL and posterior svL. We also obtained specific 1015 genes by transcriptome of O. minor brain and selected OLFM3, NPY, GnRH, and GDF8 genes. The expression of genes in the central brain showed the possibility of using NPY and GDF8 as molecular marker of compartmentation in the central brain. This study will provide useful information for establishing a molecular atlas of cephalopod brain.

Matricellular proteins in cutaneous wound healing

Cutaneous wound healing is a complex process that encompasses alterations in all aspects of the skin including the extracellular matrix (ECM). ECM consist of large structural proteins such as collagens and elastin as well as smaller proteins with mainly regulative properties called matricellular proteins. Matricellular proteins bind to structural proteins and their functions include but are not limited to interaction with cell surface receptors, cytokines, or protease and evoking a cellular response. The signaling initiated by matricellular proteins modulates differentiation and proliferation of cells having an impact on the tissue regeneration. In this review we give an overview of the matricellular proteins that have been found to be involved in cutaneous wound healing and summarize the information known to date about their functions in this process.

Calcium dysregulation potentiates wild-type myocilin misfolding: implications for glaucoma pathogenesis

Myocilin is secreted from trabecular meshwork cells to an eponymous extracellular matrix that is critical for maintaining intraocular pressure. Missense mutations found in the myocilin olfactomedin domain (OLF) lead to intracellular myocilin misfolding and are causative for the heritable form of early-onset glaucoma. The OLF domain contains a unique internal, hetero-dinuclear calcium site. Here, we tested the hypothesis that calcium dysregulation causes wild-type (WT) myocilin misfolding reminiscent of that observed for disease variants. Using two cellular models expressing WT myocilin, we show that the Ca2+ ATPase channel blocker thapsigargin inhibits WT myocilin secretion. Intracellular WT myocilin is at least partly insoluble and aggregated in the endoplasmic reticulum (ER), and stains positively with an amyloid dye. By comparing the effect of thapsigargin on WT myocilin to that on a de novo secretion-competent Ca2+-free variant D478S, we discern that non-secretion of WT myocilin is due initially to calcium dysregulation, and is potentiated further by resultant ER stress. In E. coli, depletion of calcium leads to recombinant expression of misfolded isolated WT OLF but the D478S variant is still produced as a folded monomer. Treatment of cells expressing a double mutant composed of D478S and either disease variants P370L or Y437H with thapsigargin promotes its misfolding and aggregation, demonstrating the limits of D478S to correct secretion defects. Taken together, the heterodinuclear calcium site is a liability for proper folding of myocilin. Our study suggests a molecular mechanism by which WT myocilin misfolding may contribute broadly to glaucoma-associated ER stress. This study explores the effect of calcium depletion on myocilin olfactomedin domain folding.

Transcriptomic Analysis of Breast Cancer Patients Sensitive and Resistant to Chemotherapy: Looking for Overall Survival and Drug Resistance Biomarkers

Worldwide breast cancer ranks first in mortality and incidence rates in women over 20 years old. Rather than one disease, breast cancer is a heterogeneous group of diseases that express distinct molecular profiles. Neoadjuvant chemotherapy is an important therapeutic strategy for breast cancer patients independently of their molecular subtype, with the drawback of resistance development. In addition, chemotherapy has adverse effects that combined with resistance could contribute to lower overall survival. Although great efforts have been made to find diagnostic and prognostic biomarkers for breast cancer and for response to targeted and immune therapy for this pathology, little has been explored regarding biomarkers of response to anthracyclines and taxanes based neoadjuvant chemotherapy. This work aimed to evaluate the molecular profile of patients who received neoadjuvant chemotherapy to identify differentially expressed genes (DEGs) that could be used as biomarkers of chemotherapy response and overall survival. Breast cancer patients who were candidates for neoadjuvant chemotherapy were enrolled in this study. After treatment and according to their pathological response, they were assigned as sensitive or resistant. To evaluate DEGs, Gene Ontology, Kyoto Encyclopedia Gene and Genome (KEGG), and protein–protein interactions, RNA-seq information from all patients was obtained by next-generation sequencing. A total of 1985 DEGs were found, and KEGG analysis indicated a great number of DEGs in metabolic pathways, pathways in cancer, cytokine–cytokine receptor interactions, and neuroactive ligand-receptor interactions. A selection of 73 DEGs was used further for an analysis of overall survival using the METABRIC study and the ductal carcinoma dataset of The Cancer Genome Atlas (TCGA) database. Nine DEGs correlated with overall survival, of which the subexpression of C1QTNF3, CTF1, OLFML3, PLA2R1, PODN, KRT15, HLA-A, and the overexpression of TUBB and TCP1 were found in resistant patients and related to patients with lower overall survival.

OLFML2B Is a Robust Prognostic Biomarker in Bladder Cancer Through Genome-Wide Screening: A Study Based on Seven Cohorts

Background

Bladder cancer lacks useful and robust prognostic markers to stratify patients at risk. Our study is to identify a robust prognostic marker for bladder cancer.

Methods

The transcriptome and clinical data of bladder cancer were downloaded from multiple databases. We searched for genes with robust prognosis by Kaplan-Meier analysis of the whole genome. CIBERSORT and TIMER algorithm was used to calculate the degree of immune cell infiltration.

Results

We identified OLFML2B as a robust prognostic marker for bladder cancer in five cohorts. Kaplan-Meier analysis showed that patients with a high level of OLFML2B expression had a poor prognosis. The expression of OLFML2B increased with the increase of stage and grade. We found that patients with high expression of OLFML2B still had a poor prognosis in two small bladder cancer cohorts. OLFML2B also has the prognostic ability in ten other tumors, and the prognosis is poor in high expression. The correlation analysis between OLFML2B and immune cells showed that it was positively correlated with the degree of macrophage infiltration and highly co-expressed with tumor-associated macrophage markers. Finally, the Wound-healing assay and Colony formation assay results showed that the migration and proliferation ability of bladder cancer cell lines decreased after the knockdown of OLFML2B.

Conclusions

In summary, OLFML2B is a robust risk prognostic marker, and it can help patients with bladder cancer improve individualized treatment.

OLFML2A Downregulation Inhibits Glioma Proliferation Through Suppression of Wnt/β-Catenin Signaling

Glioma is a highly heterogeneous and lethal tumor with an extremely poor prognosis. Through analysis of TCGA data, we identified that OLFML2A is a key promotor of gliomagenesis. However, the molecular function of OLFML2A and its underlying mechanism of action in glioma remain unclear. In this study, we found that OLFML2A expression was significantly upregulated in glioma specimens and positively correlated with pathological grades in glioma patients. Moreover, Kaplan–Meier survival analysis of TCGA data revealed that glioma patients with higher OLFML2A expression had shorter overall survival. Importantly, OLFML2A knockdown in glioma cells inhibited cell proliferation and promoted apoptosis. Mechanistically, OLFML2A downregulation inhibits Wnt/β-catenin signaling by upregulating amyloid precursor protein (APP) expression and reducing stabilized β-catenin levels, leading to the repression of MYC, CD44, and CSKN2A2 expression. Furthermore, OLFML2A downregulation suppressed the growth of transplanted glioma subcutaneously and intracranially by inhibiting Wnt/β-catenin pathway-dependent cell proliferation. By uncovering the oncogenic effects in human and rodent gliomas, our data support OLFML2A as a potential therapeutic target for glioma.

OLFML2A is necessary for anti-triple negative breast cancer effect of selective activator protein-1 inhibitor T-5224

Previous studies have shown that expression of activator protein-1 (AP-1) family is significantly elevated in triple-negative breast cancer (TNBC), compared with that in other breast cancer subtypes. Here we investigated the anti-tumor effect and mechanism of T-5224, an inhibitor of c-Fos/AP-1, on TNBC. We identified that T-5224 inhibited the proliferation, migration, and invasion of TNBC cells and resulted in an increase in apoptosis. Furthermore, we found that OLFML2A is a key regulatory protein acting downstream of AP-1 and is involved in T-5224-targeted AP-1 action. Multiple clinical databases online have identified that high OLFML2A level is associated with poor prognosis in TNBC patients. In summary, our experimental and bioinformatic studies indicated that OLFML2A is necessary for AP-1-overexpressing TNBC. These findings demonstrate that AP-1-overexpressing TNBC dependent on OLFML2A, and targeting both AP-1 and OLFML2A through T-5224 may be a synergistic therapeutic strategy for this clinically challenging subset of breast cancer.

Olfactomedin-like 2 A and B (OLFML2A and OLFML2B) profile expression in the retina of spotted gar (Lepisosteus oculatus) and bioinformatics mining

Olfactomedin-like (OLFML) proteins are members of the olfactomedin domain-containing secreted glycoprotein (OLF) family. OLFML2A and OLFML2B are representative molecules of these glycoproteins. Olfactomedins are critical for the development and functional organization of the nervous system and retina, which is a highly conserved structure in vertebrates, having almost identical anatomical and physiological characteristics in multiple taxa. Spotted gar, a member of the Lepisosteidae family, is a freshwater fish that inhabits rivers, bayous, swamps, and brackish waters. Recently, the complete genome has been sequenced, providing a unique bridge between fish medical models to human biology, making it an excellent animal model. This study was aimed to understanding the evolution OLFML2A and OLFML2B in the retina of spotted gar through looking for the expression of these genes. Spotted gar retina was analyzed with hematoxylin-eosin staining assays to provide an overall view of the retina structure and an immunofluorescence assay to identify OLFML2A and OLFML2B protein expression. A phylogenetic tree was created using the neighbor-joining method. Forces that direct the evolution of the fish genes were tested. Spotted gar retina, as in other vertebrates, is made of several layers. OLFML2A and OLFML2B proteins were detected in the rod and cone photoreceptor layer (PRL), outer nuclear layer (ONL), and inner nuclear layer (INL). Phylogenetic tree analysis confirms the orthology within the OLFML2A gene. Purifying selection is the evolutionary force that directs the OLFML2A genes. OLFML2A genes have a well-conserved function over time and species.

Calcium-ligand variants of the myocilin olfactomedin propeller selected from invertebrate phyla reveal cross-talk with N-terminal blade and surface helices

Olfactomedins are a family of modular proteins found in multicellular organisms that all contain five-bladed β-propeller olfactomedin (OLF) domains. In support of differential functions for the OLF propeller, the available crystal structures reveal that only some OLF domains harbor an internal calcium-binding site with ligands derived from a triad of residues. For the myocilin OLF domain (myoc-OLF), ablation of the ion-binding site (triad Asp, Asn, Asp) by altering the coordinating residues affects the stability and overall structure, in one case leading to misfolding and glaucoma. Bioinformatics analysis reveals a variety of triads with possible ion-binding characteristics lurking in OLF domains in invertebrate chordates such as Arthropoda (Asp-Glu-Ser), Nematoda (Asp-Asp-His) and Echinodermata (Asp-Glu-Lys). To test ion binding and to extend the observed connection between ion binding and distal structural rearrangements, consensus triads from these phyla were installed in the myoc-OLF. All three protein variants exhibit wild-type-like or better stability, but their calcium-binding properties differ, concomitant with new structural deviations from wild-type myoc-OLF. Taken together, the results indicate that calcium binding is not intrinsically destabilizing to myoc-OLF or required to observe a well ordered side helix, and that ion binding is a differential feature that may underlie the largely elusive biological function of OLF propellers.

Stable calcium-free myocilin olfactomedin domain variants reveal challenges in differentiating between benign and glaucoma-causing mutations

Nonsynonymous gene mutations can be beneficial, neutral, or detrimental to the stability, structure, and biological function of the encoded protein, but the effects of these mutations are often not readily predictable. For example, the β-propeller olfactomedin domain of myocilin (mOLF) exhibits a complex interrelationship among structure(s), stability, and aggregation. Numerous mutations within mOLF are linked to glaucoma; the resulting variants are less stable, aggregation-prone, and sequestered intracellularly, causing cytotoxicity. Here, we report the first stable mOLF variants carrying substitutions in the calcium-binding site that exhibit solution characteristics indistinguishable from those of glaucoma variants. Crystal structures of these stable variants at 1.8-2.0-Å resolution revealed features that we could not predict by molecular dynamics simulations, including loss of loop structure, helix unwinding, and a blade shift. Double mutants that combined a stabilizing substitution and a selected glaucoma-causing single-point mutant rescued in vitro folding and stability defects. In the context of full-length myocilin, secretion of stable single variants was indistinguishable from that of the WT protein, and the double mutants were secreted to varying extents. In summary, our finding that mOLF can tolerate particular substitutions that render the protein stable despite a conformational switch emphasizes the complexities in differentiating between benign and glaucoma-causing variants and provides new insight into the possible biological function of myocilin.

Olfactomedin-like 3: possible functions in embryonic development and tumorigenesis

Objective:

Modern medical research has proven that human diseases are directly or indirectly related to genes. At the same time, genetic research has also brought updates to diagnostic techniques. Olfactomedin-like 3 (OLFML3) gene is a novel and clinically valuable gene. In order to better understand the role of OLFML3 in human diseases, we discuss and analyze the characteristics, function, and regulation mechanism of the OLFML3 gene in this review.

Data sources:

A comprehensive search in PubMed and ScienceDirect database for English up to March 2019, with the keywords of “Olfactomedin-like 3,” “Olfactomedin,” “extracellular matrix,” “Transforming Growth Factor β1,” “anoikis-resistance,” and “microRNA-155.”

Study selection:

Careful review of all relevant literature, the references of the retrieved articles were also screened to search for potentially relevant papers.

Results:

OLFML3 is a secreted glycoprotein with 406 amino acid residues, belonging to the Olfactomedin (OLF) family. Due to the particularity of its structure and differential expression, OLFML3 has unique biological functions that could be distinct from other members in the OLF family. The currently known functions include embryonic development function and tumorigenesis. The regulation mechanism is still under investigation. It is directly related to many human diseases.

Conclusions:

OLFML3 is a multifunctional glycoprotein that is closely involved in embryonic development, tumor invasion, and metastasis. Unfortunately, current research on this important molecule is still very limited. Further investigations on the possible mechanism of OLFML3 biological functions and modulation will help us develop better diagnostics and treatments.

Olfactomedin domain-containing proteins: evolution, functional divergence, expression patterns and damaging SNPs

Olfactomedin domain-containing proteins appear to facilitate neurodevelopment, cell adhesion, intercellular interactions, and protein-protein interactions, and the disruption of their expression will lead to dramatic developmental perturbations and lethality. The aim of the present work was to study how these genes evolved in metazoans and diverged after their duplication as well as to characterize their expression profiles and detrimental mutations. We conducted an exhaustive survey of olfactomedin domain-containing genes in genomic databases, identifying 235 olfactomedin-like (OLF) proteins in 29 representative species covering all the main metazoan lineages. Phylogenetic analyses allowed us to define nine different subfamilies of OLF genes, and subfamily IX, which specifically includes two immunoglobulin domains, was identified for the first time in arthropods. Functional divergence analysis suggested that the function of this arthropod-specific OLF subfamily might have diverged from that of other subfamilies. Expression pattern analysis of OLF genes in humans and rats showed that human OLF genes tended to be highly expressed in the brain, while rat OLF genes were inclined to be expressed in the ovary and brain. We used the SIFT and PolyPhen servers in dbNSFP to distinguish deleterious mutations from neutral mutations for each member of the OLF gene family. The results showed that OLFML2B contains the most destructive SNPs (up to 61), while none of the mutations in OLFM2, OLFM4 and LPHN2 were predicted to be harmful. Taken together, these findings may not only enhance understanding of the phylogenetic relationships of the OLF family but also aid future studies on OLF protein regulation of nervous system development and immune function.

Bioinformatic exploration of OLFML2B overexpression in gastric cancer base on multiple analyzing tools

Background

Gastric cancer (GC) is one of the most commonly occuring gastrointestinal tumor types, and early diagnosis and operation have a notable effect on the prognosis of patients. Although certain markers, including HER2, VEGER-2, ERCC1 and Bcl-2, have been utilized in clinical practise to screen out new patients with GC, the results of using these markers remains poor. The role of olfactomedin-like 2B (OLFML2B) in GC, as a member of the olfactomedin domain-containing proteins family, is remain unclear.

Methods

In the present study, we assessed the expression of OLFML2B, including mRNA and protein level, by using The Cancer Genome Atlas (TCGA) database and 13 pairs of clinical samples between GC and NG tissues. The correlation between expression of OLFML2B and prognosis of GC was evaculated by the Kaplan-Meier plotter and OncoLnc online tools. In addition, mechanism analysis of OLFML2B in GC was explored thought bioinformatic tools, including cBioPortal and FunRich software.

Results

In our study, the mRNA expression of OLFML2B in GC both TCGA database and clinical samples was consistently revealed to be significantly higher compared with that in NG tissues (P < 0.0001 for TCGA database and P = 0.0034 for clinical samples), and high OLFML2B expression was found in 9 (69.23%) of 13 clinical GC by immunohistochemistry and was positively correlated with the depth of tumor invasion and clinical stage (TNM). In addition, the AUC for a ROC of 0.867 indicated a moderate diagnostic ability of OLFML2B for GC. Survival analysis from the Kaplan-Meier plotter (P = 2.6 × 10^− 6) and OncoLnc (P = 0.00276) revealed that the high expression of OLFML2B was associated with a short overall survival. Futhermore, 5% (24/478) alterations of OLFML2B were identified from cBioPortal, and among them, missense mutation (14/478) was the primary type. The results from FunRich revealed that OLFML2B participated in mediating multiple biological processes including cell growth and maintenance, regulation of the cell cycle, apoptosis and cell communication through multiple signaling pathways including the M/G1 transition pathway, post-translational protein modification and DNA replication pre-initiation.

Conclusions

Taken together, it could be deduced that OLFML2B may act as an oncogene in the development of GC and the overexpression of OLFML2B in GC may be used as a novel diagnostic and prognostic target for GC.

Arginine to Glutamine Variant in Olfactomedin Like 3 (OLFML3) Is a Candidate for Severe Goniodysgenesis and Glaucoma in the Border Collie Dog Breed

Goniodysgenesis is a developmental abnormality of the anterior chamber of the eye. It is generally considered to be congenital in dogs (Canis lupus familiaris), and has been associated with glaucoma and blindness. Goniodysgenesis and early-onset glaucoma initially emerged in Border Collies in Australia in the late 1990s and have subsequently been found in this breed in Europe and the USA. The objective of the present study was to determine the genetic basis of goniodysgenesis in Border Collies. Clinical diagnosis was based on results of examinations by veterinary ophthalmologists of affected and unaffected dogs from eleven different countries. Genotyping using the Illumina high density canine single nucleotide variant genotyping chip was used to identify a candidate genetic region. There was a highly significant peak of association over chromosome 17, with a p-value of 2 × 10-13 Expression profiles and evolutionary conservation of candidate genes were assessed using public databases. Whole genome sequences of three dogs with glaucoma, three severely affected by goniodysgenesis and three unaffected dogs identified a missense variant in the olfactomedin like 3 (OLFML3) gene in all six affected animals. This was homozygous for the risk allele in all nine cases with glaucoma and 12 of 14 other severely affected animals. Of 67 reportedly unaffected animals, only one was homozygous for this variant (offspring of parents both with goniodysgenesis who were also homozygous for the variant). Analysis of pedigree information was consistent with an autosomal recessive mode of inheritance for severe goniodysgenesis (potentially leading to glaucoma) in this breed. The identification of a candidate genetic region and putative causative variant will aid breeders to reduce the frequency of goniodysgenesis and the risk of glaucoma in the Border Collie population.

Microglia-Specific Expression of Olfml3 Is Directly Regulated by Transforming Growth Factor β1-Induced Smad2 Signaling

Microglia maturation takes place during the postnatal weeks and is characterized by the establishment of a unique microglia-specific gene expression pattern. Tmem119, Fcrls, Hexb, and Olfml3 have been identified among these microglia-specific genes. Transforming growth factor β1 (TGFβ1) has been reported as a critical factor for microglia maturation and maintenance and active TGFβ signaling precedes the inductions of microglial gene expression. In this study, we demonstrate Olfml3 expression in adult microglia and further provide evidence that TGFβ1 induces upregulation of Olfml3 expression in postnatal microglia. Using chromatin immunoprecipitation and microglia-specific silencing of TGFβ signaling in vitro and in vivo, we in clearly show that Olfml3 is a direct TGFβ1/Smad2 target gene. Together, our data underline the importance of TGFβ1 as a critical regulator of microglia functions and microglia maturation and further broaden our understanding of TGFβ1-mediated effects on the resident immune cells of the central nervous system.

Structure and Misfolding of the Flexible Tripartite Coiled-Coil Domain of Glaucoma-Associated Myocilin

Glaucoma-associated myocilin is a member of the olfactomedins, a protein family involved in neuronal development and human diseases. Molecular studies of the myocilin N-terminal coiled coil demonstrate a unique tripartite architecture: a Y-shaped parallel dimer-of-dimers with distinct tetramer and dimer regions. The structure of the dimeric C-terminal 7-heptad repeats elucidates an unexpected repeat pattern involving inter-strand stabilization by oppositely charged residues. Molecular dynamics simulations reveal an alternate accessible conformation in which the terminal inter-strand disulfide limits the extent of unfolding and results in a kinked configuration. By inference, full-length myocilin is also branched, with two pairs of C-terminal olfactomedin domains. Selected variants within the N-terminal region alter the apparent quaternary structure of myocilin but do so without compromising stability or causing aggregation. In addition to increasing our structural knowledge of naturally occurring extracellular coiled coils and biomedically important olfactomedins, this work broadens the scope of protein misfolding in the pathogenesis of myocilin-associated glaucoma.

Impaired AMPA receptor trafficking by a double knockout of zebrafish olfactomedin1a/b

The olfm1a and olfm1b genes in zebrafish encode conserved secreted glycoproteins. These genes are preferentially expressed in the brain and retina starting from 16 h post-fertilization until adulthood. Functions of the Olfm1 gene is still unclear. Here, we produced and analyzed a null zebrafish mutant of both olfm1a and olfm1b genes (olfm1 null). olfm1 null fish were born at a normal Mendelian ratio and showed normal body shape and fertility as well as no visible defects from larval stages to adult. Olfm1 proteins were preferentially localized in the synaptosomes of the adult brain. Olfm1 co-immunoprecipitated with GluR2 and soluble NSF attachment protein receptor complexes indicating participation of Olfm1 in both pre- and post-synaptic events. Phosphorylation of GluR2 was not changed while palmitoylation of GluR2 was decreased in the brain synaptosomal membrane fraction of olfm1 null compared with wt fish. The levels of GluR2, SNAP25, flotillin1, and VAMP2 were markedly reduced in the synaptic microdomain of olfm1 null brain compared with wt. The internalization of GluR2 in retinal cells and the localization of VAMP2 in brain synaptosome were modified by olfm1 null mutation. This indicates that Olfm1 may regulate receptor trafficking from the intracellular compartments to the synaptic membrane microdomain, partly through the alteration of post-translational GluR2 modifications such as palmitoylation. Olfm1 may be considered a novel regulator of the composition and function of the α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor complex.

Comparative proteome and peptidome analysis of the cephalic fluid secreted by Arapaima gigas (Teleostei: Osteoglossidae) during and outside parental care

Parental investment in Arapaima gigas includes nest building and guarding, followed by a care provision when a cephalic fluid is released from the parents’ head to the offspring. This fluid has presumably important functions for the offspring but so far its composition has not been characterised. In this study the proteome and peptidome of the cephalic secretion was studied in parental and non-parental fish using capillary electrophoresis coupled to mass spectrometry (CE-MS) and GeLC-MS/MS analyses. Multiple comparisons revealed 28 peptides were significantly different between males and parental males (PC-males), 126 between females and parental females (PC-females), 51 between males and females and 9 between PC-males and PC-females. Identification revealed peptides were produced in the inner ear (pcdh15b), eyes (tetraspanin and ppp2r3a), central nervous system (otud4, ribeye a, tjp1b and syn1) among others. A total of 422 proteins were also identified and gene ontology analysis revealed 28 secreted extracellular proteins. From these, 2 hormones (prolactin and stanniocalcin) and 12 proteins associated to immunological processes (serotransferrin, α-1-antitrypsin homolog, apolipoprotein A-I, and others) were identified. This study provides novel biochemical data on the lateral line fluid which will enable future hypotheses-driven experiments to better understand the physiological roles of the lateral line in chemical communication.

Olfactomedin 4 expression and functions in innate immunity, inflammation, and cancer

Olfactomedin 4 (OLFM4) is an olfactomedin domain-containing glycoprotein. Multiple signaling pathways and factors, including NF-κB, Wnt, Notch, PU.1, retinoic acids, estrogen receptor, and miR-486, regulate its expression. OLFM4 interacts with several other proteins, such as gene associated with retinoic-interferon-induced mortality 19 (GRIM-19), cadherins, lectins, nucleotide oligomerization domain-1 (NOD1) and nucleotide oligomerization domain-2 (NOD2), and cathepsins C and D, known to regulate important cellular functions. Recent investigations using Olfm4-deficient mouse models have provided important clues about its in vivo biological functions. Olfm4 inhibited Helicobacter pylori-induced NF-κB pathway activity and inflammation and facilitated H. pylori colonization in the mouse stomach. Olfm4-deficient mice exhibited enhanced immunity against Escherichia coli and Staphylococcus aureus infection. Olfm4 deletion in a chronic granulomatous disease mouse model rescued them from S. aureus infection. Olfm4 deletion in mice treated with azoxymethane/dextran sodium sulfate led to robust intestinal inflammation and intestinal crypt hyperplasia. Olfm4 deletion in Apc (Min/+) mice promoted intestinal polyp formation as well as adenocarcinoma development in the distal colon. Further, Olfm4-deficient mice spontaneously developed prostatic epithelial lesions as they age. OLFM4 expression is correlated with cancer differentiation, stage, metastasis, and prognosis in a variety of cancers, suggesting its potential clinical value as an early-stage cancer marker or a therapeutic target. Collectively, these data suggest that OLFM4 plays important roles in innate immunity against bacterial infection, gastrointestinal inflammation, and cancer. In this review, we have summarized OLFM4's initial characterization, expression, regulation, protein interactions, and biological functions.

Olfactomedin 2 Regulates Smooth Muscle Phenotypic Modulation and Vascular Remodeling Through Mediating Runt-Related Transcription Factor 2 Binding to Serum Response Factor

OBJECTIVE

The objective of this study is to investigate the role and underlying mechanism of Olfactomedin 2 (Olfm2) in smooth muscle cell (SMC) phenotypic modulation and vascular remodeling.

APPROACH AND RESULTS

Platelet-derived growth factor-BB induces Olfm2 expression in primary SMCs while modulating SMC phenotype as shown by the downregulation of SMC marker proteins. Knockdown of Olfm2 blocks platelet-derived growth factor-BB-induced SMC phenotypic modulation, proliferation, and migration. Conversely, Olfm2 overexpression inhibits SMC marker expression. Mechanistically, Olfm2 promotes the interaction of serum response factor with the runt-related transcription factor 2 that is induced by platelet-derived growth factor-BB, leading to a decreased interaction between serum response factor and myocardin, causing a repression of SMC marker gene transcription and consequently SMC phenotypic modulation. Animal studies show that Olfm2 is upregulated in balloon-injured rat carotid arteries. Knockdown of Olfm2 effectively inhibits balloon injury-induced neointima formation. Importantly, knockout of Olfm2 in mice profoundly suppresses wire injury-induced neointimal hyperplasia while restoring SMC contractile protein expression, suggesting that Olfm2 plays a critical role in SMC phenotypic modulation in vivo.

CONCLUSIONS

Olfm2 is a novel factor mediating SMC phenotypic modulation. Thus, Olfm2 may be a potential target for treating injury-induced proliferative vascular diseases.

Olfactomedin-like 2 A and B (OLFML2A and OLFML2B) expression profile in primates (human and baboon)

Background

The olfactomedin-like domain (OLFML) is present in at least four families of proteins, including OLFML2A and OLFML2B, which are expressed in adult rat retina cells. However, no expression of their orthologous has ever been reported in human and baboon.

Objective

The aim of this study was to investigate the expression of OLFML2A and OLFML2B in ocular tissues of baboons (Papio hamadryas) and humans, as a key to elucidate OLFML function in eye physiology.

Methods

OLFML2A and OLFML2B cDNA detection in ocular tissues of these species was performed by RT-PCR. The amplicons were cloned and sequenced, phylogenetically analyzed and their proteins products were confirmed by immunofluorescence assays.

Results

OLFML2A and OLFML2B transcripts were found in human cornea, lens and retina and in baboon cornea, lens, iris and retina. The baboon OLFML2A and OLFML2B ORF sequences have 96% similarity with their human’s orthologous. OLFML2A and OLFML2B evolution fits the hypothesis of purifying selection. Phylogenetic analysis shows clear orthology in OLFML2A genes, while OLFML2B orthology is not clear.

Conclusions

Expression of OLFML2A and OLFML2B in human and baboon ocular tissues, including their high similarity, make the baboon a powerful model to deduce the physiological and/or metabolic function of these proteins in the eye.

Mutated olfactomedin 1 in the interphotoreceptor matrix of the mouse retina causes functional deficits and vulnerability to light damage

Olfactomedin 1 (OLFM1) is a secreted glycoprotein and member of the olfactomedin protein family, which is preferentially expressed in various areas throughout the central nervous system. To learn about the functional properties of OLFM1 in the eye, we investigated its localization in the mouse and pig eye. In addition, we analyzed the ocular phenotype of Olfm1 mutant mice in which 52 amino acids were deleted in the central part (M2 region) of OLFM1. OLFM1 was detected in cornea, sclera, retina, and optic nerve of both wild-type and Olfm1 mutant littermates. By immunohistochemistry and double labeling with the lectin peanut agglutinin, OLFM1 was found in the interphotoreceptor matrix (IPM) of mouse and pig retina where it was directly localized to the inner segments of photoreceptors. Western blotting confirmed the presence of the OLFM1 isoforms pancortin 1 (BMY) and pancortin 2 (BMZ) in the IPM. The retinal phenotype of Olfm1 mutant mice did not obviously differ from that of wild-type littermates. In addition, outer nuclear layer (ONL) and total retinal thickness were not different, and the same was true for the area of the optic nerve in cross sections. Functional changes were observed though by electroretinography, which showed significantly lower a- and b-wave amplitudes in Olfm1 mutant mice when compared to age-matched wild-type mice. When light damage experiments were performed as an experimental paradigm of photoreceptor apoptosis, significantly more TUNEL-positive cells were observed in Olfm1 mutant mice 30 h after light exposure. One week after light exposure, the ONL was significantly thinner in Olfm1 mutant mice than in wild-type littermates indicating increased photoreceptor loss. No differences were observed when rhodopsin turnover or ERK1/2 signaling was investigated. We conclude that OLFM1 is a newly identified IPM molecule that serves an important role for photoreceptor homeostasis, which is significantly compromised in the eyes of Olfm1 mutant mice.

A quantitative proteomics study on olfactomedin 4 in the development of gastric cancer

Gastric cancer (GC) is now one of the most common malignancies with a relatively high incidence and high mortality rate. The prognosis is closely related to the degree of tumor metastasis. The mechanism of metastasis is still unclear. Proteomics analysis is a powerful tool to study and evaluate protein expression in tumor tissues. In the present study, we collected 15 gastric cancer and adjacent normal gastric tissues and used the isobaric tags for relative and absolute quantitation (iTRAQ) method to identify differentially expressed proteins. A total of 134 proteins were differentially expressed between the cancerous and non-cancerous samples. Azurocidin 1 (AZU1), CPVL, olfactomedin 4 (OLFM4) and Villin 1 (VIL1) were upregulated and confirmed by western blot analysis, real-time quantitative PCR and immunohistochemical analyses. These results were in accordance with iTRAQ. Furthermore, silencing the OLFM4 expression suppressed the migration, invasion and proliferation of the GC cells in vitro. The present study represents a successful application of the iTRAQ method in analyzing the expression levels of thousands of proteins. Overexpression of OLFM4 in gastric cancer may induce the development of gastric cancer. Overall, suppression of OLFM4 expression may be a promising strategy in the development of novel cancer therapeutic drugs.

Olfactomedin 1 Deficiency Leads to Defective Olfaction and Impaired Female Fertility

Olfactomedin 1 (OLFM1) is a glycoprotein highly expressed in the brain. Olfm1(-/-) female mice were previously reported to have reduced fertility. Previous microarray analysis revealed Olfm1 among the most highly upregulated genes in the uterine luminal epithelium upon embryo implantation, which was confirmed by in situ hybridization. We hypothesized that Olfm1 deficiency led to defective embryo implantation and thus impaired fertility. Indeed, Olfm1(-/-) females had defective embryo implantation. However, Olfm1(-/-) females rarely mated and those that mated rarely became pregnant. Ovarian histology indicated the absence of corpora lutea in Olfm1(-/-) females, indicating defective ovulation. Superovulation using equine chorionic gonadotropin-human chorionic gonadotropin rescued mating, ovulation, and pregnancy, and equine chorionic gonadotropin alone rescued ovulation in Olfm1(-/-) females. Olfm1(-/-) females had a 13% reduction of hypothalamic GnRH neurons but comparable basal serum LH levels and GnRH-induced LH levels compared with wild-type controls. These results indicated no obvious local defects in the female reproductive system and a functional hypothalamic-pituitary-gonadal axis. Olfm1(-/-) females were unresponsive to the effects of male bedding stimulation on pubertal development and estrous cycle. There were 41% fewer cFos-positive cells in the mitral cell layer of accessory olfactory bulb upon male urine stimulation for 90 minutes. OLFM1 was expressed in the main and accessory olfactory systems including main olfactory epithelium, vomeronasal organ, main olfactory bulb, and accessory olfactory bulb, with the highest expression detected in the axon bundles of olfactory sensory neurons. These data demonstrate that defective fertility in Olfm1(-/-) females is most likely a secondary effect of defective olfaction.

Molecular Details of Olfactomedin Domains Provide Pathway to Structure-Function Studies

Olfactomedin (OLF) domains are found within extracellular, multidomain proteins in numerous tissues of multicellular organisms. Even though these proteins have been implicated in human disorders ranging from cancers to attention deficit disorder to glaucoma, little is known about their structure(s) and function(s). Here we biophysically, biochemically, and structurally characterize OLF domains from H. sapiens olfactomedin-1 (npoh-OLF, also called noelin, pancortin, OLFM1, and hOlfA), and M. musculus gliomedin (glio-OLF, also called collomin, collmin, and CRG-L2), and compare them with available structures of myocilin (myoc-OLF) recently reported by us and R. norvegicus glio-OLF and M. musculus latrophilin-3 (lat3-OLF) by others. Although the five-bladed β-propeller architecture remains unchanged, numerous physicochemical characteristics differ among these OLF domains. First, npoh-OLF and glio-OLF exhibit prominent, yet distinct, positive surface charges and copurify with polynucleotides. Second, whereas npoh-OLF and myoc-OLF exhibit thermal stabilities typical of human proteins near 55°C, and most myoc-OLF variants are destabilized and highly prone to aggregation, glio-OLF is nearly 20°C more stable and significantly more resistant to chemical denaturation. Phylogenetically, glio-OLF is most similar to primitive OLFs, and structurally, glio-OLF is missing distinguishing features seen in OLFs such as the disulfide bond formed by N- and C- terminal cysteines, the sequestered Ca²⁺ ion within the propeller central hydrophilic cavity, and a key loop-stabilizing cation-π interaction on the top face of npoh-OLF and myoc-OLF. While deciphering the explicit biological functions, ligands, and binding partners for OLF domains will likely continue to be a challenging long-term experimental pursuit, we used structural insights gained here to generate a new antibody selective for myoc-OLF over npoh-OLF and glio-OLF as a first step in overcoming the impasse in detailed functional characterization of these biomedically important protein domains.

Structural basis for misfolding in myocilin-associated glaucoma

Olfactomedin (OLF) domain-containing proteins play roles in fundamental cellular processes and have been implicated in disorders ranging from glaucoma, cancers and inflammatory bowel disorder, to attention deficit disorder and childhood obesity. We solved crystal structures of the OLF domain of myocilin (myoc-OLF), the best studied such domain to date. Mutations in myoc-OLF are causative in the autosomal dominant inherited form of the prevalent ocular disorder glaucoma. The structures reveal a new addition to the small family of five-bladed β-propellers. Propellers are most well known for their ability to act as hubs for protein-protein interactions, a function that seems most likely for myoc-OLF, but they can also act as enzymes. A calcium ion, sodium ion and glycerol molecule were identified within a central hydrophilic cavity that is accessible via movements of surface loop residues. By mapping familial glaucoma-associated lesions onto the myoc-OLF structure, three regions sensitive to aggregation have been identified, with direct applicability to differentiating between neutral and disease-causing non-synonymous mutations documented in the human population worldwide. Evolutionary analysis mapped onto the myoc-OLF structure reveals conserved and divergent regions for possible overlapping and distinctive functional protein-protein or protein-ligand interactions across the broader OLF domain family. While deciphering the specific normal biological functions, ligands and binding partners for OLF domains will likely continue to be a challenging long-term experimental pursuit, atomic detail structural knowledge of myoc-OLF is a valuable guide for understanding the implications of glaucoma-associated mutations and will help focus future studies of this biomedically important domain family.

Deletion of olfactomedin 2 induces changes in the AMPA receptor complex and impairs visual, olfactory, and motor functions in mice

Olfactomedin 2 (Olfm2) is a secretory glycoprotein belonging to the family of olfactomedin domain-containing proteins. A previous study has shown that a mutation in OLFM2 is associated with primary open angle glaucoma in Japanese patients. In the present study, we generated Olfm2 deficient mice by replacing the Olfm2 gene with the LacZ gene. The loss of Olfm2 resulted in no gross abnormalities. However, Olfm2 null mice showed reduced exploration, locomotion, olfactory sensitivity, abnormal motor coordination, and anxiety related behavior. The pattern of the Olfm2 gene expression was studied in the brain and eye using β-galactosidase staining. In the brain, Olfm2 was mainly expressed in the olfactory bulb, cortex, piriform cortex, olfactory trabeculae, and inferior and superior colliculus. In the eye expression was detected mainly in retinal ganglion cells. In Olfm2 null mice, the amplitude of the first negative wave in the visual evoked potential test was significantly reduced as compared with wild-type littermates. Olfm2, similar to Olfm1, interacted with the GluR2 subunit of the AMPAR complexes and Olfm2 co-segregated with the AMPA receptor subunit GluR2 and other synaptic proteins in the synaptosomal membrane fraction upon biochemical fractionation of the adult mice cortex and retina. Immunoprecipitation from the synaptosomal membrane fraction of the Olfm2 null mouse brain cortex using the GluR2 antibody showed reduced levels of several components of the AMPAR complex in the immunoprecipitates including Olfm1, PSD95 and CNIH2. These results suggest that heterodimers of Olfm1 and Olfm2 interact with AMPAR more efficiently than Olfm2 homodimers and that Olfm2 plays a role in the organization of the AMPA receptor complexes.

Olfactomedin proteins: central players in development and disease

Olfactomedin proteins are characterized by a conserved domain of \texorpdfstring~\textasciitilde250 amino acids corresponding to the olfactomedin archetype first discovered in olfactory neuroepithelium. They arose early in evolution and occur throughout the animal kingdom. In mice and humans olfactomedin proteins comprise a diverse array of glycoproteins, many of which are critical for early development and functional organization of the nervous system as well as hematopoiesis. Olfactomedin domains appear to facilitate protein-protein interactions, intercellular interactions, and cell adhesion. Several members of the family have been implicated in various common diseases, notably myocilin in glaucoma and OLFM4 in cancer. This review highlights this important, hitherto understudied family of proteins.

In-depth proteomic analysis of mouse cochlear sensory epithelium by mass spectrometry

Proteomic analysis of sensory organs such as the cochlea is challenging due to its small size and difficulties with membrane protein isolation. Mass spectrometry in conjunction with separation methods can provide a more comprehensive proteome, because of the ability to enrich protein samples, detect hydrophobic proteins, and identify low abundant proteins by reducing the proteome dynamic range. GELFrEE as well as different separation and digestion techniques were combined with FASP and nanoLC-MS/MS to obtain an in-depth proteome analysis of cochlear sensory epithelium from 30-day-old mice. Digestion with LysC/trypsin followed by SCX fractionation and multiple nanoLC-MS/MS analyses identified 3773 proteins with a 1% FDR. Of these, 694 protein IDs were in the plasmalemma. Protein IDs obtained by combining outcomes from GELFrEE/LysC/trypsin with GELFrEE/trypsin/trypsin generated 2779 proteins, of which 606 additional proteins were identified using the GELFrEE/LysC/trypsin approach. Combining results from the different techniques resulted in a total of 4620 IDs, including a number of previously unreported proteins. GO analyses showed high expression of binding and catalytic proteins as well as proteins associated with metabolism. The results show that the application of multiple techniques is needed to provide an exhaustive proteome of the cochlear sensory epithelium that includes many membrane proteins. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium with the data set identifier PXD000231.

Olfactomedin-like 3 (OLFML3) gene expression in baboon and human ocular tissues: cornea, lens, uvea, and retina

BACKGROUND

Olfactomedin-like is a family of polyfunctional polymeric glycoproteins. This family has at least four members. One member of this family is OLFML3, which is preferentially expressed in placenta but is also detected in other adult tissues including the liver and heart. However, its orthologous rat gene is expressed in the iris, sclera, trabecular meshwork, retina, and optic nerve.

METHODS

OLFML3 messenger amplification was performed by RT-PCR from human and baboon ocular tissues. The products were cloned and sequenced.

RESULTS

We report OLFML3 expression in human and baboon eye. The full coding DNA sequence has 1221 bp, from which an open reading frame of 406 amino acid was obtained. The baboon OLFML3 gene nucleotidic sequence has 98% and amino acidic 99% similarity with humans.

CONCLUSIONS

OLFML3 gene expression in human and baboon ocular tissues and its high similarity make the baboon a powerful model to deduce the physiological and/or metabolic function of this protein in the eye.

OLFML3 expression is decreased during prenatal muscle development and regulated by microRNA-155 in pigs

The Olfactomedin-like 3 (OLFML3) gene has matrix-related function involved in embryonic development. MicroRNA-155 (miR-155), 21- to 23-nucleotides (nt) noncoding RNA, regulated myogenesis by target mRNA. Our LongSAGE analysis suggested that OLFML3 gene was differently expressed during muscle development in pig. In this study, we cloned the porcine OLFML3 gene and detected its tissues distribution in adult Tongcheng pigs and dynamical expression in developmental skeletal muscle (12 prenatal and 10 postnatal stages) from Landrace (lean-type) and Tongcheng (obese-type) pigs. Subsequently, we analyzed the interaction between OLFML3 and miR-155. The OLFML3 was abundantly expressed in liver and pancreas, moderately in lung, small intestine and placenta, and weakly in other tissues and postnatal muscle. There were different dynamical expression patterns between Landrace and Tongcheng pigs during prenatal skeletal muscle development. The OLFML3 was down-regulated (33-50 days post coitus, dpc), subsequently up-regulated (50-70 dpc), and then down-regulated (70-100 dpc) in Landrace pigs, while in Tongcheng pigs, it was down-regulated (33-50 dpc), subsequently up-regulated (50-55 dpc) and then down-regulated (55-100 dpc). There was higher expression in Tongcheng than Landrace in prenatal muscle from 33 to 60 dpc, and opposite situation from 65 to 100 dpc. Dual luciferase assay and real time PCR documented that OLFML3 expression was regulated by miR-155 at mRNA level. Our research indicated that OLFML3 gene may affect prenatal skeletal muscle development and was regulated by miR-155. These finding will help understanding biological function and expression regulation of OLFML3 gene in mammal animals.

OLFM4 is associated with lymph node metastasis and poor prognosis in patients with gastric cancer

PURPOSE

The present study investigated the clinical significance of the relationship between olfactomedin 4 (OLFM4) expression and the clinicopathological features of patients with gastric cancer.

METHODS

Tumor tissue and adjacent normal tissue, lymph nodes, and peritoneal metastases were analyzed by the Affymetrix GeneChip(®) HG-U133A2.0 array. The expression of OLFM4 was detected by real-time quantitative RT-PCR in gastric tumor tissue and adjacent normal tissue. OLFM4 expression was analyzed by immunohistochemistry in 436 clinicopathologically characterized gastric cancer cases and in corresponding distant metastases from 61 patients.

RESULTS

A total of 434 genes and 169 expressed sequence tags were upregulated, including OLFM4. The expression of OLFM4 mRNA or protein differed significantly among gastric tumor tissue, matched normal gastric mucosa, and lymph node metastases. Further multivariate analysis suggested that lymph node metastases and distant metastases, TNM stage, and expression of OLFM4 were independent prognostic indicators for gastric cancer.

CONCLUSION

Gene expression profiles were useful for simultaneously analyzing the expression levels of thousands of genes. Reduced expression of OLFM4 in gastric cancer is associated significantly with lymph node and distant metastases and with poor prognosis. OLFM4 may prove to be an important molecular marker for predicting the carcinogenesis, development, progression, and metastasis of gastric cancer.

Keeping an eye on myocilin: a complex molecule associated with primary open-angle glaucoma susceptibility

MYOC encodes a secretary glycoprotein of 504 amino acids named myocilin. MYOC is the first gene to be linked to juvenile open-angle glaucoma (JOAG) and some forms of adult-onset primary open-angle glaucoma (POAG). The gene was identified as an up-regulated molecule in cultured trabecular meshwork (TM) cells after treatment with dexamethasone and was originally referred to as trabecular meshwork-inducible glucocorticoid response (TIGR). Elevated intraocular pressure (IOP), due to decreased aqueous outflow, is the strongest known risk factor for POAG. Increasing evidence showed that the modulation of the wild-type (wt) myocilin protein expression is not causative of glaucoma while some misfolded and self-assembly aggregates of mutated myocilin may be associated with POAG in related or unrelated populations. The etiology of the disease remains unclear. Consequently, a better understanding of the molecular mechanisms underlyingPOAG is required to obtain early diagnosis, avoid potential disease progression, and develop new therapeutic strategies. In the present study, we review and discuss the most relevant studies regarding structural characterizations, expressions, molecular interactions, putative functions of MYOC gene and/or its corresponding protein in POAG etiology.

Olfactomedin 2: expression in the eye and interaction with other olfactomedin domain-containing proteins

PURPOSE

Olfactomedin 2 (OLFM2) belongs to the family of olfactomedin domain-containing proteins. Genetic data suggest its association with glaucoma in Japanese patients. However, its functions are still elusive. In this study, the properties of mammalian OLFM2 were investigated.

METHODS

Expression of the rat and mouse Olfm2 gene was studied by using real-time PCR and in situ hybridization. Substitutions were introduced into OLFM2 by mutagenesis in vitro. Intracellular localization of OLFM2 was studied by confocal microscopy after transient transfection in HEK293 cells. Interaction of OLFM2 with olfactomedin 1 (Olfm1), olfactomedin 3 (Olfm3), myocilin, and gliomedin was studied by using co-immunoprecipitation.

RESULTS

Two major human OLFM2 mRNAs encode secreted proteins with a length of 454 and 478 amino acids. OLFM2 is more closely related to OLFM1 and -3 than to any other family members. Olfm2 showed the most dynamic expression pattern compared with Olfm1 and -3 during mouse eye development and was expressed preferentially in the developing retinal ganglion cell layer. Among three OLFM2 substitutions tested (T86M, R144Q, and L420S), only L420S completely blocked secretion of the protein. OLFM2 interacted with Olfm1 and -3, but not with myocilin and gliomedin. Co-transfection of the L420S mutant with wild-type Olfm1 and -3 significantly inhibited secretion of Olfm1 and -3.

CONCLUSIONS

Highly conserved OLFM2 protein may play an important role in the course of retinal and eye development. Severe mutations in one of the closely related olfactomedin domain-containing proteins (Olfm1-3) may block the secretion and probably the activity of all three family members, leading to more pronounced diseases of the retina than the knockout of individual genes.

Stem cell marker olfactomedin 4: critical appraisal of its characteristics and role in tumorigenesis

Olfactomedin 4 (OLFM4), a member of the olfactomedin domain-containing proteins, is a glycoprotein with molecular weight of approximately 64 kDa. The protein is a "robust marker" of Lgr5+ stem cells and has been localised to mitochondria, nuclei and cell membranes. The bulk of OLFM4 exists in a polymeric form which is held together by disulfide bonds and carbohydrate interactions. Earlier studies revealed that the protein binds to lectins and cadherins, and facilitates cell-cell adhesion. Recent data demonstrated that the protein possesses several hallmarks of carcinogenesis. OLFM4 has also been purported to be an inducible resistance factor to apoptotic stimuli such as radiation and anticancer drugs. Here, we review its synonyms and classification, gene structure, protein structure, intracellular and tissue distribution, adhesive and antiapoptotic; mitotic; migratory and cell cycle regulatory characteristics. We also critically evaluate recent advances in understanding of the transcriptional regulation of OLFM4 and its upstream signalling pathways with special emphasis on carcinogenesis and outline future perspectives in the field.

Olfactomedin 4 is a marker for progression of cervical neoplasia

INTRODUCTION

Olfactomedin 4 (OLFM4) is expressed in gastrointestinal cancers and related to progression and differentiation of these malignancies. However, whether OLFM4 contributes to tumorigenesis of other tissues has not been thoroughly investigated. The purpose of the study was to investigate OLFM4 expression in cervical epithelium and its association with progression of cervical neoplasia and differentiation of cervical carcinomas.

METHODS

Immunohistochemistry and real-time reverse transcription-polymerase chain reaction were used to evaluate the expression and distribution of OLFM4 in cervical intraepithelial neoplasia (CIN) and invasive squamous cell carcinomas (ISCCs).

RESULTS

The overall positive OLFM4 staining levels in normal cervical epithelia, CIN I, CIN II, CIN III, and ISCCs are 22.0%, 94.2%, 93.7%, 94.6%, and 96.7%, respectively. The intensity of OLFM4 staining was enhanced according to increased pathologic grade of cervical squamous intraepithelial lesion. The immunoreactivity to OLFM4 was stronger in well-differentiated ISCCs than in poorly differentiated ISCCs.

CONCLUSIONS

Olfactomedin 4 expression has been associated with progression of CIN and differentiation of cervical cancer. The results provide new evidence that OLFM4 plays an important role in tumorigenesis in the female reproductive tract.

The extracellular regulation of bone morphogenetic protein signaling

In many cases, the level, positioning and timing of signaling through the bone morphogenetic protein (BMP) pathway are regulated by molecules that bind BMP ligands in the extracellular space. Whereas many BMP-binding proteins inhibit signaling by sequestering BMPs from their receptors, other BMP-binding proteins cause remarkably context-specific gains or losses in signaling. Here, we review recent findings and hypotheses on the complex mechanisms that lead to these effects, with data from developing systems, biochemical analyses and mathematical modeling.

Systems biology of the self-regulating morphogenetic gradient of the Xenopus gastrula

The morphogenetic field concept was proposed by experimental embryologists to account for the self-regulative behavior of embryos. Such fields have remained an abstract concept until the recent identification of their molecular components using a combination of genetics, biochemistry, and theoretical modeling. One of the best studied models of a morphogenetic field is the Dorsal-Ventral (D-V) patterning of the early frog embryo. This patterning system is regulated by the bone morphogenetic protein (BMP) signaling pathway and an intricate network of secreted protein antagonists. This biochemical pathway of interacting proteins functions in the extracellular space to generate a D-V gradient of BMP signaling, which is maintained during extensive morphogenetic movements of cell layers during gastrulation. The D-V field is divided into a dorsal and a ventral center, in regions of low and high BMP signaling respectively, under opposite transcriptional control by BMPs. The robustness of the patterning is assured at two different levels. First, in the extracellular space by secreted BMP antagonists that generate a directional flow of BMP ligands to the ventral side. The flow is driven by the regulated proteolysis of the Chordin inhibitor and by the presence of a molecular sink on the ventral side that concentrates BMP signals. The tolloid metalloproteinases and the Chordin-binding protein Crossveinless-2 (CV2) are key components of this ventral sink. Second, by transcriptional feedback at the cellular level: The dorsal and ventral signaling centers adjust their size and level of BMP signaling by transcriptional feedback. This allows cells on one side of a gastrula containing about 10,000 cells to communicate with cells in the opposite pole of the embryo.

Glaucoma-associated myocilin: a better understanding but much more to learn

Over a decade has passed since myocilin was identified as the first gene linked to early and late-onset primary open-angle glaucoma. During this time, considerable effort has been put forth to understand the functional role myocilin has in normal and glaucomatous eyes. Myocilin is expressed in many ocular and non-ocular tissues, is found in both intracellular and extracellular spaces, and has been linked to elevations in intraocular pressure. Mutations in the myocilin gene that have been associated with glaucoma appear to confer a gain-of-functional activity rather than loss of function. Unfortunately, what the normal function of myocilin is and how alterations in the function can confer a glaucoma phenotype have yet to be elucidated. We will review the current understanding of myocilin with special emphasis on the structural makeup of the myocilin gene and protein, its possible physiological roles internal and external to ocular cells, the regulation of intraocular pressure as evidenced through the use of perfusion culture systems and animal models, and as a causative agent in some forms of glaucoma.

Myocilin is a modulator of Wnt signaling

It is well documented that mutations in the MYOCILIN gene may lead to juvenile- and adult-onset primary open-angle glaucoma. However, the functions of wild-type myocilin are still not well understood. To study the functions of human myocilin and its two proteolytic fragments, these proteins were expressed in HEK293 cells. Conditioned medium from myocilin-expressing cells, as well as purified myocilin, induced the formation of stress fibers in primary cultures of human trabecular meshwork or NIH 3T3 cells. Stress fiber-inducing activity of myocilin was blocked by antibodies against myocilin, as well as secreted inhibitors of Wnt signaling, secreted Frizzled-related protein 1 (sFRP1) or sFRP3, and beta-catenin small interfering RNA. Interaction of myocilin with sFRP1, sFRP3, and several Frizzled receptors was confirmed by immunoprecipitation experiments and by binding of myocilin to the surface of cells expressing cysteine-rich domains of different Frizzled and sFRPs. Treatment of NIH 3T3 cells with myocilin and its fragments induced intracellular redistribution of beta-catenin and its accumulation on the cellular membrane but did not induce nuclear accumulation of beta-catenin. Overexpression of myocilin in the eye angle tissues of transgenic mice stimulated accumulation of beta-catenin in these tissues. Myocilin and Wnt proteins may perform redundant functions in the mammalian eye, since myocilin modulates Wnt signaling by interacting with components of this signaling pathway.

Raf kinase inhibitory protein (RKIP): a physiological regulator and future therapeutic target

BACKGROUND

Raf kinase inhibitory protein (RKIP) belongs to the phosphatidylethanolamine binding protein (PEBP) family that is expressed in both prokaryotic and euakaryotic organisms.

OBJECTIVE

In this review, we discuss the role of RKIP as a modulator of signal transduction, the relationship of RKIP to other members of the PEBP family, and the role of RKIP in human health and disease.

RESULTS/CONCLUSION

In mammals, RKIP regulates activation of MAPK, NF-kappaB and G protein coupled receptors (GPCRs). As a modulator of key signaling pathways, RKIP affects various cellular processes including cell differentiation, the cell cycle, apoptosis and cell migration. Emerging evidence suggests that RKIP is implicated in several human diseases or disorders, among them metastatic tumorigenesis and Alzheimer's disease.

Zebrafish olfactomedin 1 regulates retinal axon elongation in vivo and is a modulator of Wnt signaling pathway

Olfactomedin 1 (Olfm1) is a secreted glycoprotein belonging to a family of olfactomedin domain-containing proteins. It is involved in the regulation of neural crest production in chicken and promotes neuronal differentiation in Xenopus. Here, we investigate the functions of Olfm1 in zebrafish eye development. Overexpression of full-length Olfm1, and especially its BMY form lacking the olfactomedin domain, increased the thickness of the optic nerve and produced a more extended projection field in the optic tectum compared with control embryos. In contrast, injection of olfm1-morpholino oligonucleotide (Olfm1-MO) reduced the eye size, inhibited optic nerve extension, and increased the number of apoptotic cells in the retinal ganglion cell and inner nuclear layers. Overexpression of full-length Olfm1 increased the lateral separation of the expression domains of eye-field markers, rx3 and six3. The Olfm1-MO had the opposite effect. These data suggest that zebrafish Olfm1 may play roles in the early eye determination, differentiation, optic nerve extension, and branching of the retinal ganglion cell axon terminals, with the N-terminal region of Olfm1 being critical for these effects. Injection of RNA encoding WIF-1, a secreted inhibitor of Wnt signaling, caused changes in the expression pattern of rx3 similar to those observed after Olfm1-MO injection. Simultaneous overexpression of WIF-1 and Olfm1 abolished the WIF-1 effect. Physical interaction of WIF-1 and Olfm1 was demonstrated by coimmunoprecipitation experiments. We concluded that Olfm1 serves as a modulator of Wnt signaling.