Expression of the nidogen-binding site of the laminin gamma1 chain disturbs basement membrane formation and maintenance in F9 embryoid bodies

The novel protein complex FAPα/ITGA5 is involved in the bone destruction of apical periodontitis

The bacteria that invade the periapical tissue of teeth can directly damage tissue cells such as periapical fibroblasts, leading to an inflammatory response in the periapical tissue and ultimately resulting in bone destruction. We investigated the role of fibroblast activation protein α (FAPα) and integrin α5 (ITGA5) in periapical bone destruction. This study found that FAPα and ITGA5 were highly expressed in human tissues from patients with chronic apical periodontitis. Osteoclast differentiation decreased when FAPα or ITGA5 was silenced and inhibited. The results of protein molecular docking showed that FAPα had good binding affinity to ITGA5, and its free energy was -14.5 kcal/mol. Immunofluorescence staining and co-immunoprecipitation showed that FAPα and ITGA5 formed protein complexes in the inflammatory microenvironment. In conclusion, this study proved that FAPα and ITGA5 participate in the regulation of osteoclast differentiation by forming protein complexes in the inflammatory microenvironment, which then regulates the occurrence and development of chronic apical periodontitis.

Respiratory chain inactivation links cartilage-mediated growth retardation to mitochondrial diseases

Children with mitochondrial diseases often present with slow growth and short stature, but the underlying mechanism remains unclear. In this study, Holzer et al. provide in vivo evidence that mitochondrial respiratory chain dysfunction induces cartilage degeneration coincident with altered metabolism, impaired extracellular matrix formation, and cell death at the cartilage–bone junction.

In childhood, skeletal growth is driven by transient expansion of cartilage in the growth plate. The common belief is that energy production in this hypoxic tissue mainly relies on anaerobic glycolysis and not on mitochondrial respiratory chain (RC) activity. However, children with mitochondrial diseases causing RC dysfunction often present with short stature, which indicates that RC activity may be essential for cartilage-mediated skeletal growth. To elucidate the role of the mitochondrial RC in cartilage growth and pathology, we generated mice with impaired RC function in cartilage. These mice develop normally until birth, but their later growth is retarded. A detailed molecular analysis revealed that metabolic signaling and extracellular matrix formation is disturbed and induces cell death at the cartilage–bone junction to cause a chondrodysplasia-like phenotype. Hence, the results demonstrate the overall importance of the metabolic switch from fetal glycolysis to postnatal RC activation in growth plate cartilage and explain why RC dysfunction can cause short stature in children with mitochondrial diseases.

Identification of Nidogen 1 as a lung metastasis protein through secretome analysis

Secreted proteins play crucial roles in mediating tumor-stroma interactions during metastasis of cancer to different target organs. To comprehensively profile secreted proteins involved in lung metastasis, we applied quantitative mass spectrometry-based proteomics and identified 392 breast cancer-derived and 302 melanoma-derived proteins secreted from highly lung metastatic cells. The cancer-specific lung metastasis secretome signatures (LMSSs) displayed significant prognostic value in multiple cancer clinical data sets. Moreover, we observed a significant overlap of enriched pathways between the LMSSs of breast cancer and melanoma despite an overall small overlap of specific proteins, suggesting that common biological processes are executed by different proteins to enable the two cancer types to metastasize to the lung. Among the novel candidate lung metastasis proteins, Nidogen 1 (NID1) was confirmed to promote lung metastasis of breast cancer and melanoma, and its expression is correlated with poor clinical outcomes. In vitro functional analysis further revealed multiple prometastatic functions of NID1, including enhancing cancer cell migration and invasion, promoting adhesion to the endothelium and disrupting its integrity, and improving vascular tube formation capacity. As a secreted prometastatic protein, NID1 may be developed as a new biomarker for disease progression and therapeutic target in breast cancer and melanoma.

Nidogen-1 Degraded by Cathepsin S can be Quantified in Serum and is Associated with Non-Small Cell Lung Cancer

Loss of basement membrane (BM) integrity is typically associated with cancer. Nidogen-1 is an essential component of the BM. Nidogen-1 is a substrate for cathepsin-S (CatS) which is released into the tumor microenvironment. Measuring nidogen-1 degraded by CatS may therefore have biomarker potential in cancer. The aim of this study was to investigate if CatS-degraded nidogen-1 was detectable in serum and a possible biomarker for cancer, a pathology associated with disruption of the BM. A competitive enzyme-linked immunosorbent assay (NIC) was developed with a monoclonal mouse antibody specific for a CatS cleavage site on human nidogen-1. Dilution and spiking recovery, inter- and intravariation, as well as accuracy were evaluated. Serum levels were evaluated in patients with breast cancer, small cell lung cancer (SCLC), and non-SCLC (NSCLC) and in healthy controls. The results indicated that the NIC assay was specific for nidogen-1 cleaved by CatS. Inter- and intraassay variations were 9% and 14%, respectively. NIC was elevated in NSCLC as compared to healthy controls (P<.001), breast cancer (P<.01), and SCLC (P<.5). The diagnostic power (area under the receiver operating characteristics) of NIC for NSCLC as compared to all other samples combined was 0.83 (95% confidence interval: 0.71-0.95), P<.0001. In conclusion, nidogen-1 degraded by CatS can be quantified in serum by the NIC assay. The current data strongly suggest that cathepsin-S degradation of nidogen-1 is strongly associated with NSCLC, which needs validation in larger clinical cohorts.

Laminin: loss-of-function studies

Laminin, one of the most widely expressed extracellular matrix proteins, exerts many important functions in multiple organs/systems and at various developmental stages. Although its critical roles in embryonic development have been demonstrated, laminin's functions at later stages remain largely unknown, mainly due to its intrinsic complexity and lack of research tools (most laminin mutants are embryonic lethal). With the advance of genetic and molecular techniques, many new laminin mutants have been generated recently. These new mutants usually have a longer lifespan and show previously unidentified phenotypes. Not only do these studies suggest novel functions of laminin, but also they provide invaluable animal models that allow investigation of laminin's functions at late stages. Here, I first briefly introduce the nomenclature, structure, and biochemistry of laminin in general. Next, all the loss-of-function mutants/models for each laminin chain are discussed and their phenotypes compared. I hope to provide a comprehensive review on laminin functions and its loss-of-function models, which could serve as a reference for future research in this understudied field.

LAMC1 gene is associated with premature ovarian failure

OBJECTIVES

Common variations with modest effect in complex and polygenic disease such as premature ovarian failure (POF) can be detected by a genome wide association study. We performed a genome wide association study to identify predisposing genes associated with an increased risk of POF.

STUDY DESIGN

In stage I, genome wide association study was performed using 24 POF patients and 24 matched controls. A strongly associated region was re-tested to confirm the association with POF in stage II using 98 patients and 218 matched controls.

RESULTS

In the stage I, we found a strongly associated region that was located on chromosome 1q31 and encoded the laminin gamma 1 (LAMC1) gene. All 22 single nucleotide polymorphisms (SNPs) in the LAMC1 formed a linkage disequilibrium block and two haplotypes were significantly associated with POF. In the stage II, 14 SNPs, the majority of which were SNPs located in coding region and tagging SNPs, were genotyped. Distributions of 9 SNPs of them including one nonsynonymous SNP (rs20558) and one haplotype (HT1, C-C-T-G-C-C-A-T-T-C) were significantly higher in POF patients than in control group (86.6% and 74.5%, respectively, OR=2.209, CI: 1.139-4.284, P=0.017).

CONCLUSIONS

We showed for the first time that LAMC1 is significantly associated with POF, and specifically, possession of at least one HT1 was associated with susceptibility to POF. This result means that HT1 may co-exist with causative variant for susceptibility to POF in linkage disequilibrium and that the LAMC1 may be involved in POF pathogenesis.

Basement membrane deposition of nidogen 1 but not nidogen 2 requires the nidogen binding module of the laminin gamma1 chain

The nidogen-laminin interaction is proposed to play a key role in basement membrane (BM) assembly. However, though there are similarities, the phenotypes in mice lacking nidogen 1 and 2 (nidogen double null) differ to those of mice lacking the nidogen binding module (γ1III4) of the laminin γ1 chain. This indicates different cell- and tissue-specific functions for nidogens and their interaction with laminin and poses the question of whether the phenotypes in nidogen double null mice are caused by the loss of the laminin-nidogen interaction or rather by other unknown nidogen functions. To investigate this, we analyzed BMs, in particular those in the skin of mice lacking the nidogen binding module. In contrast to nidogen double null mice, all skin BMs in γ1III4-deficient mice appeared normal. Furthermore, although nidogen 1 deposition was strongly reduced, nidogen 2 appeared unchanged. Mice with additional deletion of the laminin γ3 chain, which contains a γ1-like nidogen binding module, showed a further reduction of nidogen 1 in the dermoepidermal BM; however, this again did not affect nidogen 2. This demonstrates that in vivo only nidogen 1 deposition is critically dependent on the nidogen binding modules of the laminin γ1 and γ3 chains, whereas nidogen 2 is independently recruited either by binding to an alternative site on laminin or to other BM proteins.

Fluorescent proteins and their applications in imaging living cells and tissues

Green fluorescent protein (GFP) from the jellyfish Aequorea victoria and its homologs from diverse marine animals are widely used as universal genetically encoded fluorescent labels. Many laboratories have focused their efforts on identification and development of fluorescent proteins with novel characteristics and enhanced properties, resulting in a powerful toolkit for visualization of structural organization and dynamic processes in living cells and organisms. The diversity of currently available fluorescent proteins covers nearly the entire visible spectrum, providing numerous alternative possibilities for multicolor labeling and studies of protein interactions. Photoactivatable fluorescent proteins enable tracking of photolabeled molecules and cells in space and time and can also be used for super-resolution imaging. Genetically encoded sensors make it possible to monitor the activity of enzymes and the concentrations of various analytes. Fast-maturing fluorescent proteins, cell clocks, and timers further expand the options for real time studies in living tissues. Here we focus on the structure, evolution, and function of GFP-like proteins and their numerous applications for in vivo imaging, with particular attention to recent techniques.

Laminin deposition in the extracellular matrix: a complex picture emerges

Laminins are structural components of basement membranes. In addition, they are key extracellular-matrix regulators of cell adhesion, migration, differentiation and proliferation. This Commentary focuses on a relatively understudied aspect of laminin biology: how is laminin deposited into the extracellular matrix? This topic has fascinated researchers for some time, particularly considering the diversity of patterns of laminin that can be visualized in the matrix of cultured cells. We discuss current ideas of how laminin matrices are assembled, the role of matrix receptors in this process and how laminin-associated proteins modulate matrix deposition. We speculate on the role of signaling pathways that are involved in laminin-matrix deposition and on how laminin patterns might play an important role in specifying cell behaviors, especially directed migration. We conclude with a description of new developments in the way that laminin deposition is being studied, including the use of tagged laminin subunits that should allow the visualization of laminin-matrix deposition and assembly by living cells.

Seizure-related gene 6 (Sez-6) in amacrine cells of the rodent retina and the consequence of gene deletion

Background

Seizure-related gene 6 (Sez-6) is expressed in neurons of the mouse brain, retina and spinal cord. In the cortex, Sez-6 plays a role in specifying dendritic branching patterns and excitatory synapse numbers during development.

Methodology/Principal Findings

The distribution pattern of Sez-6 in the retina was studied using a polyclonal antibody that detects the multiple isoforms of Sez-6. Prominent immunostaining was detected in GABAergic, but not in AII glycinergic, amacrine cell subpopulations of the rat and mouse retina. Amacrine cell somata displayed a distinct staining pattern with the Sez-6 antibody: a discrete, often roughly triangular-shaped bright spot positioned between the nucleus and the apical dendrite superimposed over weaker general cytoplasmic staining. Displaced amacrines in the ganglion cell layer were also positive for Sez-6 and weaker staining was occasionally observed in neurons with the morphology of alpha ganglion cells. Two distinct Sez-6 positive strata were present in the inner plexiform layer in addition to generalized punctate staining. Certain inner nuclear layer cells, including bipolar cells, stained more weakly and diffusely than amacrine cells, although some bipolar cells exhibited a perinuclear “bright spot” similar to amacrine cells. In order to assess the role of Sez-6 in the retina, we analyzed the morphology of the Sez-6 knockout mouse retina with immunohistochemical markers and compared ganglion cell dendritic arbor patterning in Sez-6 null retinae with controls. The functional importance of Sez-6 was assessed by dark-adapted paired-flash electroretinography (ERG).

Conclusions

In summary, we have reported the detailed expression pattern of a novel retinal marker with broad cell specificity, useful for retinal characterization in rodent experimental models. Retinal morphology, ganglion cell dendritic branching and ERG waveforms appeared normal in the Sez-6 knockout mouse suggesting that, in spite of widespread expression of Sez-6, retinal function in the absence of Sez-6 is not affected.

Nidogens-Extracellular matrix linker molecules

Nidogens/entactins are a family of highly conserved, sulfated glycoproteins. Biochemical studies have implicated them as having a major structural role in the basement membrane. However despite being ubiquitous components of this specialized extracellular matrix and having a wide spectrum of binding partners, genetic analysis has shown that they are not required for the overall architecture of the basement membrane. Rather in development they play an important role in its stabilization especially in tissues undergoing rapid growth or turnover. Nidogen breakdown has been implicated as a key event in the basement membrane degradation occurring in mammary gland involution. A number of studies, most compellingly those in C. elegans, demonstrated that nidogens may have other nonstructural roles and be involved in axonal pathfinding and synaptic transmission.

Basement membranes in skin are differently affected by lack of nidogen 1 and 2

Nidogens have been proposed to play a key role in basement membrane (BM) formation. However, recent findings using genetic approaches and organotypic coculture models demonstrated distinct tissue requirements thus changing the classical view of BM assembly. Toward this end, we have analyzed the dermo-epidermal junction and the microvasculature in skin of nidogen-deficient mice for their BM composition and structural assembly. Histology of nidogen double-null embryos at embryonic day (E)18.5 revealed overall normal skin morphology with a regularly differentiated epidermis. However, in the dermis, numerous erythrocytes had extravasated out of the microvasculature. Residual composition and ultrastructure of the dermo-epidermal BM are not altered in the absence of nidogens, demonstrating that the deposition of laminin, collagen IV, and perlecan occurs and allows cutaneous BM formation. In contrast, in capillaries, BM formation is severely impaired in the absence of nidogens, showing an irregular, patchy distribution and a dramatically reduced deposition of collagen IV, perlecan, and particularly laminin-411. Ultrastructure revealed thin fragile walls in the small blood vessels next to the epidermis, completely lacking a distinct endothelial BM. In summary, our results indicate that in skin the laminin composition of the various BMs determines whether nidogens are required for their assembly and stabilization.

Directed Differentiation of Human Embryonic Stem Cells into the Pancreatic Endocrine Lineage

Human embryonic stem (hES) cells represent a potentially unlimited source of transplantable beta-cells for the treatment of diabetes. Here we describe a differentiation strategy that reproducibly directs HES3, an National Institutes of Health (NIH)-registered hES cell line, into cells of the pancreatic endocrine lineage. HES3 cells are removed from their feeder layer and cultured as embryoid bodies in a three-dimensional matrix in the presence of Activin A and Bmp4 to induce definitive endoderm. Next, growth factors known to promote the proliferation and differentiation of pancreatic ductal epithelial cells to glucose-sensing, insulin-secreting beta-cells are added. Pdx1 expression, which identifies pancreatic progenitors, is detected as early as day 12 of differentiation. By day 34, Pdx1+ cells comprise between 5% and 20% of the total cell population and Insulin gene expression is up-regulated, with release of C-peptide into the culture medium. Unlike another recent report of the induction of insulin+ cells in differentiated hES cell populations, we are unable to detect the expression of other pancreatic hormones in insulin+ cells. When transplanted into severe combined immunodeficiency (SCID) mice, differentiated cell populations retain their endocrine identity and synthesize insulin.

Three-dimensional extracellular matrix stimulates gastrulation-like events in human embryoid bodies

Human embryonic stem (hES) cells cultured in suspension form aggregates called embryoid bodies (EBs), which structurally resemble the pregastrulation-stage embryo. We show that these EBs express genes characteristic of the visceral endoderm (VE) and form an outer boundary of VE-like cells, but only a minority expresses markers of the primitive streak and the definitive endoderm in patterns suggestive of gastrulation-like events. EBs embedded in a Matrigel matrix, however, lack the presumptive VE but up-regulate expression of gastrulation-related genes, which is correlated with the expression of these genes in a greater proportion of individual EBs. Over time, Matrigelembedded EBs form internally organized structures and exhibit higher expression of markers of the definitive endoderm and mesoderm. We hypothesize that a three-dimensional adhesive support provides an organizing influence analogous to the early basal lamina surrounding the epiblast of the pregastrulation embryo. Furthermore, we identify a synthetic three-dimensional scaffold capable of supporting EB formation that partially mimics the effects of Matrigel.

Lack of Nidogen-1 and -2 Prevents Basement Membrane Assembly in Skin-Organotypic Coculture

Nidogens are considered as classical linkers joining laminin and collagen IV networks in basement membranes (BMs); however, recent genetic approaches have suggested that nidogens function in a tissue-specific and developmental context. Thus, in mice lacking both nidogen-1 and -2 heart and lung were severely affected, causing neonatal death. Furthermore, in various locations, extravasation of erythrocytes was observed implying microvascular defects. Mice expressing solely either isoform, had a functional BM, although nidogen-2 binds with lower affinity to the laminin gamma1 chain. Having previously blocked BM formation by interfering with nidogen-1 binding to laminin in skin-organotypic cocultures, here we investigated the roles of nidogen-1 and -2 in this model. For that purpose, human HaCaT cells were grown in three-dimensional cocultures on collagen matrices containing murine fibroblasts of varying nidogen deficiency. As with our experiments blocking laminin-nidogen interaction, lack of both nidogens completely prevented BM deposition and ultrastructural assembly of BM and hemidesmosomes, although other BM proteins remained detectable at comparable levels with no signs of degradation. Supplementation by recombinant nidogen-1 or -2 restored these structures, as shown by immunofluorescence and electron microscopy, confirming that in this system nidogen-2 is equivalent to nidogen-1, and both can promote the development of a functional BM zone.

Loss of Nidogen-1 and -2 Results in Syndactyly and Changes in Limb Development

Nidogens are two ubiquitous basement membrane proteins produced mainly by mesenchymal cells. Nidogen-mediated interactions, in particular with laminin, collagen IV, and perlecan have been considered important in the formation and maintenance of the basement membrane. However, whereas mice lacking both nidogen isoforms or carrying mutations in the high affinity nidogen-binding site upon the laminin gamma1 chain have specific basement membrane defects in certain organs, particularly in the lung, characterization of these mice has also shown that basement membrane formation per se does not need nidogens or the laminin-nidogen interaction. Limb development requires the complex interplay of numerous growth factors whose expression is dependent upon the apical ectodermal ridge. Here, we show that lack of nidogen-1 and -2 results in a specific and time-limited failure in the ectodermal basement membrane of the limb bud. The absence of this basement membrane leads to aberrant apical ectodermal ridge formation. It also causes altered distribution of growth factors, such as fibroblast growth factors and leads to a fully penetrant soft tissue syndactyly caused by the dysregulation of interdigital apoptosis. Further, in certain animals more severe changes in bone formation occur, providing evidence for the interplay between growth factors and the extracellular matrix.

Compound genetic ablation of nidogen 1 and 2 causes basement membrane defects and perinatal lethality in mice

Nidogen 1 and 2 are basement membrane glycoproteins, and previous biochemical and functional studies indicate that they may play a crucial role in basement membrane assembly. While they show a divergent expression pattern in certain adult tissues, both have a similar distribution during development. Gene knockout studies in mice demonstrated that the loss of either isoform has no effect on basement membrane formation and organ development, suggesting complementary functions. Here, we show that this is indeed the case. Deficiency of both nidogens in mice resulted in perinatal lethality. Nidogen 1 and 2 do not appear to be crucial in establishing tissue architecture during organ development; instead, they are essential for late stages of lung development and for maintenance and/or integrity of cardiac tissue. These organ defects are not compatible with postnatal survival. Ultrastructural analysis suggests that the phenotypes directly result from basement membrane changes. However, despite the ubiquitous presence of nidogens in basement membranes, defects do not occur in all tissues or in all basement membranes, suggesting a varying spectrum of roles for nidogens in the basement membrane.

Inhibition of basement membrane formation by a nidogen-binding laminin gamma1-chain fragment in human skin-organotypic cocultures

Basement membranes generally determine different tissue compartments in complex organs, such as skin, playing not only an important structural but also a regulatory role. We have previously demonstrated the formation of a regular basement membrane in organotypic three-dimensional (3D)-cocultures of human skin keratinocytes and fibroblasts by indirect immunofluorescence and transmission electron microscopy. In this assembly process, cross-linking of type IV collagen and the laminin gamma1 chain by nidogen is considered a crucial step. For a functional proof, we have now competitively inhibited nidogen binding to laminin in 3D-cocultures with a recombinant laminin gamma1 fragment (gamma1III3-5 module) spanning this binding site. Repeated treatment abolished the deposition of nidogen at the epithelial-matrix interface but also greatly perturbed the presence of other matrix constituents such as laminin and perlecan. This effect persisted over the entire observation period of 10 to 21 days. In contrast, some components of the basement membrane zone were only moderately affected, with the laminin-5 isoform (gamma2 chain), type IV collagen and integrin alpha6ss4 still showing a distinct staining at their regular position, when seen by light microscopy. Furthermore, epidermal morphology and differentiation remained largely normal as indicated by the regular location of keratins K1/K10 and also of late differentiation markers. Ultrastructural examination demonstrated that the gamma1 fragment completely suppressed any formation of basement membrane structures (lamina densa) and also of hemidesmosomal adhesion complexes. As a consequence of hemidesmosome deficiency, keratin filament bundles were not attached to the ventral basal cell aspect. These findings were further substantiated by immuno-electron microscopy, revealing either loss or drastic reduction and dislocation of basement membrane and hemidesmosomal components. Taken together, in this simplified human skin model (representing a 'closed system') a functional link has been demonstrated between compound structures of the extra- and intracellular space at the junctional zone providing a basis to interfere at distinct points and in a controlled fashion.

GFP-like proteins as ubiquitous metazoan superfamily: evolution of functional features and structural complexity

Homologs of the green fluorescent protein (GFP), including the recently described GFP-like domains of certain extracellular matrix proteins in Bilaterian organisms, are remarkably similar at the protein structure level, yet they often perform totally unrelated functions, thereby warranting recognition as a superfamily. Here we describe diverse GFP-like proteins from previously undersampled and completely new sources, including hydromedusae and planktonic Copepoda. In hydromedusae, yellow and nonfluorescent purple proteins were found in addition to greens. Notably, the new yellow protein seems to follow exactly the same structural solution to achieving the yellow color of fluorescence as YFP, an engineered yellow-emitting mutant variant of GFP. The addition of these new sequences made it possible to resolve deep-level phylogenetic relationships within the superfamily. Fluorescence (most likely green) must have already existed in the common ancestor of Cnidaria and Bilateria, and therefore GFP-like proteins may be responsible for fluorescence and/or coloration in virtually any animal. At least 15 color diversification events can be inferred following the maximum parsimony principle in Cnidaria. Origination of red fluorescence and nonfluorescent purple-blue colors on several independent occasions provides a remarkable example of convergent evolution of complex features at the molecular level.