The requirement of the glutamic acid residue at the third position from the carboxyl termini of the laminin gamma chains in integrin binding by laminins

Heparan Sulfate Chain-Conjugated Laminin-E8 Fragments Advance Paraxial Mesodermal Differentiation Followed by High Myogenic Induction from hiPSCs

Human-induced pluripotent stem cells (hiPSCs) have great therapeutic potential. The cell source differentiated from hiPSCs requires xeno-free and robust methods for lineage-specific differentiation. Here, a system is described for differentiating hiPSCs on new generation laminin fragments (NGLFs), a recombinant form of a laminin E8 fragment conjugated to the heparan sulfate chains (HS) attachment domain of perlecan. Using NGLFs, hiPSCs are highly promoted to direct differentiation into a paraxial mesoderm state with high-efficiency muscle lineage generation. HS conjugation to the C-terminus of Laminin E8 fragments brings fibroblast growth factors (FGFs) bound to the HS close to the cell surface of hiPSCs, thereby facilitating stronger FGF signaling pathways stimulation and initiating HOX gene expression, which triggers the paraxial mesoderm differentiation of hiPSCs. This highly efficient differentiation system can provide a roadmap for paraxial mesoderm development and an infinite source of myocytes and muscle stem cells for disease modeling and regenerative medicine.

Polymerizing laminins in development, health, and disease

Polymerizing laminins are multi-domain basement membrane (BM) glycoproteins that self-assemble into cell-anchored planar lattices to establish the initial BM scaffold. Nidogens, collagen-IV and proteoglycans then bind to the scaffold at different domain loci to create a mature BM. The LN domains of adjacent laminins bind to each other to form a polymer node, while the LG domains attach to cytoskeletal-anchoring integrins and dystroglycan, as well as to sulfatides and heparan sulfates. The polymer node, the repeating unit of the polymer scaffold, is organized into a near-symmetrical triskelion. The structure, recently solved by cryo-electron microscopy in combination with AlphaFold2 modeling and biochemical studies, reveals how the LN surface residues interact with each other and how mutations cause failures of self-assembly in an emerging group of diseases, the LN-lamininopathies, that include LAMA2-related dystrophy and Pierson syndrome.

Recombinant Laminin-511 Fragment (iMatrix-511) Coating Supports Maintenance of Human Nucleus Pulposus Progenitor Cells In Vitro

The angiopoietin-1 receptor (Tie2) marks specific nucleus pulposus (NP) progenitor cells, shows a rapid decline during aging and intervertebral disc degeneration, and has thus sparked interest in its utilization as a regenerative agent against disc degeneration. However, the challenge of maintaining and expanding these progenitor cells in vitro has been a significant hurdle. In this study, we investigated the potential of laminin-511 to sustain Tie2+ NP progenitor cells in vitro. We isolated cells from human NP tissue (n = 5) and cultured them for 6 days on either standard (Non-coat) or iMatrix-511 (laminin-511 product)-coated (Lami-coat) dishes. We assessed these cells for their proliferative capacity, activation of Erk1/2 and Akt pathways, as well as the expression of cell surface markers such as Tie2, GD2, and CD24. To gauge their regenerative potential, we examined their extracellular matrix (ECM) production capacity (intracellular type II collagen (Col2) and proteoglycans (PG)) and their ability to form spherical colonies within methylcellulose hydrogels. Lami-coat significantly enhanced cell proliferation rates and increased Tie2 expression, resulting in a 7.9-fold increase in Tie2-expressing cell yields. Moreover, the overall proportion of cells positive for Tie2 also increased 2.7-fold. Notably, the Col2 positivity rate was significantly higher on laminin-coated plates (Non-coat: 10.24% (±1.7%) versus Lami-coat: 26.2% (±7.5%), p = 0.010), and the ability to form spherical colonies also showed a significant improvement (Non-coat: 40.7 (±8.8)/1000 cells versus Lami-coat: 70.53 (±18.0)/1000 cells, p = 0.016). These findings demonstrate that Lami-coat enhances the potential of NP cells, as indicated by improved colony formation and proliferative characteristics. This highlights the potential of laminin-coating in maintaining the NP progenitor cell phenotype in culture, thereby supporting their translation into prospective clinical cell-transplantation products.

Laminin fragments conjugated with perlecan's growth factor-binding domain differentiate human induced pluripotent stem cells into skin-derived precursor cells

Deriving stem cells to regenerate full-thickness human skin is important for treating skin disorders without invasive surgical procedures. Our previous protocol to differentiate human induced pluripotent stem cells (iPSCs) into skin-derived precursor cells (SKPs) as a source of dermal stem cells employs mouse fibroblasts as feeder cells and is therefore unsuitable for clinical use. Herein, we report a feeder-free method for differentiating iPSCs into SKPs by customising culture substrates. We immunohistochemically screened for laminins expressed in dermal papillae (DP) and explored the conditions for inducing the differentiation of iPSCs into SKPs on recombinant laminin E8 (LM-E8) fragments with or without conjugation to domain I of perlecan (PDI), which binds to growth factors through heparan sulphate chains. Several LM-E8 fragments, including those of LM111, 121, 332, 421, 511, and 521, supported iPSC differentiation into SKPs without PDI conjugation. However, the SKP yield was significantly enhanced on PDI-conjugated LM-E8 fragments. SKPs induced on PDI-conjugated LM111-E8 fragments retained the gene expression patterns characteristic of SKPs, as well as the ability to differentiate into adipocytes, osteocytes, and Schwann cells. Thus, PDI-conjugated LM-E8 fragments are promising agents for inducing iPSC differentiation into SKPs in clinical settings.

Exogenous laminin exhibits a unique vascular pattern in the brain via binding to dystroglycan and integrins

BACKGROUND

Unlike other proteins that exhibit a diffusion pattern after intracerebral injection, laminin displays a vascular pattern. It remains unclear if this unique vascular pattern is caused by laminin-receptor interaction or laminin self-assembly.

METHODS

We compared the distribution of various wild-type laminin isoforms in the brain after intracerebral injection. To determine what causes the unique vascular pattern of laminin in the brain, laminin mutants with impaired receptor-binding and/or self-assembly activities and function-blocking antibodies to laminin receptors were used. In addition, the dynamics of laminin distribution and elimination were examined at multiple time points after intracerebral injection.

RESULTS

We found that β2-containing laminins had higher affinity for the vessels compared to β1-containing laminins. In addition, laminin mutants lacking receptor-binding domains but not that lacking self-assembly capability showed substantially reduced vascular pattern. Consistent with this finding, dystroglycan (DAG1) function-blocking antibody significantly reduced the vascular pattern of wild-type laminin-111. Although failed to affect the vascular pattern when used alone, integrin-β1 function-blocking antibody further decreased the vascular pattern when combined with DAG1 antibody. EDTA, which impaired laminini-DAG1 interaction by chelating Ca²⁺, also attenuated the vascular pattern. Immunohistochemistry revealed that laminins were predominantly located in the perivascular space in capillaries and venules/veins but not arterioles/arteries. The time-course study showed that laminin mutants with impaired receptor-engaging activity were more efficiently eliminated from the brain compared to their wild-type counterparts. Concordantly, significantly higher levels of mutant laminins were detected in the cerebral-spinal fluid (CSF).

CONCLUSIONS

These findings suggest that intracerebrally injected laminins are enriched in the perivascular space in a receptor (DAG1/integrin)-dependent rather than self-assembly-dependent manner and eliminated from the brain mainly via the perivascular clearance system.

Junctional epidermolysis bullosa: genotype-phenotype correlations

Junctional epidermolysis bullosa most commonly results from mutations in theLAMA3, LAMB3, LAMC2, COL17A1, ITGA6 and ITGB4genes. Junctional epidermolysis bullosa is characterized by clinical heterogeneity. To date, scientific findings allow to evaluate correlations between the severity of clinical manifestations and genetic defects underlying in the development of the disease. A systematic literature search was performed using PubMed and RSCI, and keywords including junctional epidermolysis bullosa, laminin 332, collagen XVII, 64 integrin. The review includes description of clinical findings of junctional epidermolysis bullosa, mutation location and types, its impact on protein production and functions. To evaluate the impact of gene mutation on protein functions, this review explores the structure and functions of lamina lucida components, including laminin 332, collagen XVII and 64 integrin, which are frequently associated with the development of junctional epidermolysis bullosa. The correlation between severe types of junctional epidermolysis bullosa and mutations resulting in premature stop codon generation and complete absence of protein expression has been described. Although, genotype-phenotype correlations should be analyzed carefully due to mechanisms which enable to improve protein expression.

Cell-specific expression and function of laminin at the neurovascular unit

Laminin, a major component of the basal lamina (BL), is a heterotrimeric protein with many isoforms. In the CNS, laminin is expressed by almost all cell types, yet different cells synthesize distinct laminin isoforms. By binding to its receptors, laminin exerts a wide variety of important functions. However, due to the reciprocal and cell-specific expression of laminin in different cells at the neurovascular unit, its functions in blood-brain barrier (BBB) maintenance and BBB repair after injury are not fully understood. In this review, we focus on the expression and functions of laminin and its receptors in the neurovascular unit under both physiological and pathological conditions. We first briefly introduce the structures of laminin and its receptors. Next, the expression and functions of laminin and its receptors in the CNS are summarized in a cell-specific manner. Finally, we identify the knowledge gap in the field and discuss key questions that need to be answered in the future. Our goal is to provide a comprehensive overview on cell-specific expression of laminin and its receptors in the CNS and their functions on BBB integrity.

Defective perlecan-associated basement membrane regeneration and altered modulation of transforming growth factor beta in corneal fibrosis

In the cornea, the epithelial basement membrane (EBM) and corneal endothelial Descemet's basement membrane (DBM) critically regulate the localization, availability and, therefore, the functions of transforming growth factor (TGF)β1, TGFβ2, and platelet-derived growth factors (PDGF) that modulate myofibroblast development. Defective regeneration of the EBM, and notably diminished perlecan incorporation, occurs via several mechanisms and results in excessive and prolonged penetration of pro-fibrotic growth factors into the stroma. These growth factors drive mature myofibroblast development from both corneal fibroblasts and bone marrow-derived fibrocytes, and then the persistence of these myofibroblasts and the disordered collagens and other matrix materials they produce to generate stromal scarring fibrosis. Corneal stromal fibrosis often resolves completely if the inciting factor is removed and the BM regenerates. Similar defects in BM regeneration are likely associated with the development of fibrosis in other organs where perlecan has a critical role in the modulation of signaling by TGFβ1 and TGFβ2. Other BM components, such as collagen type IV and collagen type XIII, are also critical regulators of TGF beta (and other growth factors) in the cornea and other organs. After injury, BM components are dynamically secreted and assembled through the cooperation of neighboring cells-for example, the epithelial cells and keratocytes for the corneal EBM and corneal endothelial cells and keratocytes for the corneal DBM. One of the most critical functions of these reassembled BMs in all organs is to modulate the pro-fibrotic effects of TGFβs, PDGFs and other growth factors between tissues that comprise the organ.

Laminin-511-derived recombinant fragment and Rho kinase inhibitor Y-27632 facilitate serial cultivation of keratinocytes differentiated from human embryonic stem cells

INTRODUCTION

Keratinocytes derived from pluripotent stem cells have a short proliferative lifespan under conventional culture conditions that are optimized for keratinocytes. Recently, a Rho kinase inhibitor, Y-27632, had been used as a standard supplement for culture medium in which the proliferative lifespan of postnatal keratinocytes was markedly expanded. In addition, recombinant human laminin-511 was demonstrated to be an adhesive ligand for promoting proliferation of cultured epidermal keratinocytes. Based on this knowledge, efficacies of Y-27632 and a laminin511-derived recombinant fragment, known as laminin-511 E8 fragment (LN-511-E8), were evaluated for establishing cultivation methods of keratinocyte differentiated from human embryonic stem cells (hESC).

METHODS

Differentiated cells from hESCs, which were established with clinical grade in previous study, were seeded onto culture dishes coated with LN-511-E8 and co-cultured with a mouse feeder layer in serum-free medium supplemented with Y-27632. Before serial cultivation, hESC-derived keratinocytes were separated from other differentiated cells by trypsinization. The isolated hESC-derived keratinocytes were used for evaluating clonogenicity, gene expression analysis for keratinocyte markers, potency of terminal differentiation by air-lifting culture, and long-term proliferation activity by serial cultivation. Moreover, efficacies of Y-27632, LN-511-E8, and mouse feeder layer were evaluated on proliferation of hESC-derived keratinocytes.

RESULTS

hESC-derived keratinocytes with activity of clonal growth were successfully isolated by trypsinization and exhibited potency of differentiation to form stratified epidermal equivalents with expressions of progenitor and differentiation markers of epidermal keratinocyte. Y-27632 and LN-511-E8 were required for maintaining the proliferative activity of the hESC-derived keratinocytes in serially cultivation using mouse feeder layer with stable doubling time during logarithmic growth phase.

CONCLUSIONS

These results indicate the utility of Y-27632 and LN-511-E8 for serial cultivation of hESC-derived keratinocytes, which have a potential for fabricating allogeneic cellular products in clinical situations for regeneration of stratified epithelial tissues.

Canine junctional epidermolysis bullosa due to a novel mutation in LAMA3 with severe upper respiratory involvement

BACKGROUND

Junctional epidermolysis bullosa (JEB) is a group of congenital blistering skin diseases characterized by clefting through the lamina lucida of the basement membrane zone.

OBJECTIVES

To characterize the clinical and morphological features of a congenital mechanobullous disease in a litter of puppies with severe upper respiratory involvement, and to identify an associated genetic variant.

ANIMALS

Five of eight puppies in an Australian cattle dog cross-bred litter showed signs of skin fragility. Three were stillborn and one died at one month of age. The two surviving puppies were presented with blistering skin disease and severe respiratory distress. Additionally, one unaffected sibling was examined and blood was obtained for genetic testing.

METHODS AND MATERIALS

Post-mortem examination, histopathological evaluation and electron microscopy were performed. Whole genome sequencing (WGS) of one affected puppy was compared to a database of 522 dogs of 55 different breeds for variant analysis. Sanger sequencing of one additional affected and one unaffected sibling confirmed the variant.

RESULTS

Clinically, severe mucocutaneous ulcers occurred in frictional areas with claw sloughing. Histopathological results revealed subepidermal clefts and electron microscopy confirmed the split in the lamina lucida. Post-mortem examination documented extensive pharyngeal and laryngeal lesions with granulation tissue and fibrinous exudate obscuring the airway. Moderate tracheal hypoplasia contributed. The WGS revealed a novel missense variant in the laminin α3-chain XP_537297.2p(Asp2867Val), with an autosomal recessive mode of inheritance.

CONCLUSIONS AND CLINICAL RELEVANCE

A novel variant in LAMA3 caused a generalized and severe phenotype of JEB with an unique clinical presentation of upper airway obstruction.

Structural mechanism of laminin recognition by integrin

Recognition of laminin by integrin receptors is central to the epithelial cell adhesion to basement membrane, but the structural background of this molecular interaction remained elusive. Here, we report the structures of the prototypic laminin receptor α6β1 integrin alone and in complex with three-chain laminin-511 fragment determined via crystallography and cryo-electron microscopy, respectively. The laminin-integrin interface is made up of several binding sites located on all five subunits, with the laminin γ1 chain C-terminal portion providing focal interaction using two carboxylate anchor points to bridge metal-ion dependent adhesion site of integrin β1 subunit and Asn189 of integrin α6 subunit. Laminin α5 chain also contributes to the affinity and specificity by making electrostatic interactions with large surface on the β-propeller domain of α6, part of which comprises an alternatively spliced X1 region. The propeller sheet corresponding to this region shows unusually high mobility, suggesting its unique role in ligand capture.

Laminins and interaction partners in the architecture of the basement membrane at the dermal-epidermal junction

The basement membrane at the dermal-epidermal junction keeps the epidermis attached to the dermis. This anatomical barrier is made up of four categories of extracellular matrix proteins: collagen IV, laminin, nidogen and perlecan. These proteins are precisely arranged in a well-defined architecture through specific interactions between the structural domains of the individual components. Some of the molecular constituents are provided by both fibroblasts and keratinocytes, while others are synthesized exclusively by fibroblasts or keratinocytes. It remains to be determined how the components from the fibroblasts are targeted to the dermal-epidermal junction and correctly organized and integrated with the proteins from the adjacent keratinocytes to form the basement membrane.

Chemically defined human vascular laminins for biologically relevant culture of hiPSC-derived brain microvascular endothelial cells

BACKGROUND

In recent years, differentiation of human induced pluripotent stem cells (hiPSCs) into brain-specific microvascular endothelial cells (iBMECs) has frequently been used to model the blood-brain barrier (BBB). However, there are limitations in the use of iBMECs for in vitro studies, such as transendothelial electrical resistance (TEER) instability, weak junctional expression of VE-cadherin, and lack of proper fluid shear stress response. In vivo, the basement membrane (BM) composition of the BBB evolves throughout development, and laminins become the dominant component of the mature vascular BM. However, laminin isoforms of the endothelial BM have not been used for culture of differentiated iBMECs. The main goal of this study is to investigate the effect of different laminin isoforms of the endothelial BM on iBMEC functionality and to determine whether better recapitulation of the physiological BM in vitro can address the aforementioned limitations of iBMECs.

METHODS

Using a previously reported method, hiPSCs were differentiated into iBMECs. The influence of main laminins of the endothelial BM, LN 411 and LN 511, on iBMEC functionality was studied and compared to a collagen IV and fibronectin mixture (CN IV-FN). Quantitative RT-PCR, immunocytochemistry, and TEER measurement were utilized to assess gene and protein expression and barrier properties of iBMECs on different extracellular matrices. Single-channel microfluidic devices were used to study the effect of shear stress on iBMECs.

RESULTS

LN 511, but not LN 411, improved iBMEC barrier properties and resulted in more sustained TEER stability. Immunocytochemistry showed improved junctional protein expression compared to iBMECs cultured on CN IV-FN. iBMECs cultured on LN 511 showed a reduction of stress fibers, indicating resting endothelial phenotype, whereas gene expression analysis revealed upregulation of multiple genes involved in endothelial activation in iBMECs on CN IV-FN. Finally, culturing iBMECs on LN 511 enhanced physiological responses to shear stress, including morphological changes and enhanced junctional protein association.

CONCLUSION

LN 511 improves the functionality and long-term barrier stability of iBMECs. Our findings suggest that incorporation of physiologically relevant LN 511 in iBMEC culture would be beneficial for disease modeling applications and BBB-on-a-chip platforms that accommodate fluid flow.

Potential mechanisms of action of celastrol against rheumatoid arthritis: Transcriptomic and proteomic analysis

The clinical efficacy for treating of celastrol rheumatoid arthritis (RA) has been well-documented, but its mechanism of action remains unclear. Here we explored through what proteins and processes celastrol may act in activated fibroblast-like synoviocytes (FLS) from RA patients. Differential expression of genes and proteins after celastrol treatment of FLS was examined using RNA sequencing, label-free relatively quantitative proteomics and molecular docking. In this paper, expression of 26,565 genes and 3,372 proteins was analyzed. Celastrol was associated with significant changes in genes that respond to oxidative stress and oxygen levels, as well as genes that stabilize or synthesize components of the extracellular matrix. These results identify several potential mechanisms through which celastrol may inhibit inflammation in RA.

Enhanced osteogenesis of human mesenchymal stem cells by self-assembled peptide hydrogel functionalized with glutamic acid templated peptides

Self-assembling peptide (SAP) hydrogel has been shown to be an excellent biological material for three-dimensional cell culture and stimulatie cell migration and differentiation into the scaffold, as well as for repairing bone tissue defects. Herein, we designed one of the SAP scaffolds KLD (KLDLKLDLKLDL) through direct coupling to short bioactive motif O1 (EEGGC) and O2 (EEEEE) of which bioactivity on osteogenic differentiation was previously demonstrated and self-assembled in different concentrations (0.5%, 1%, and 2%). Our aim was to enhance osteogenesis and biomineralization of injectable SAP hydrogels with controlled mechanical properties so that the peptide hydrogel also becomes capable of being injected to bone defects. The molecular integration of the nanofibrous peptide scaffolds was observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The rheological properties and degradation profile of SAP hydrogels were evaluated to ensure stability of SAPs. Compared with pure KLD scaffold, we found that these designed bioactive peptide scaffolds significantly promoted hMSCs proliferation depicted by biochemical analysis of alkaline phosphatase (ALP) activity, total calcium deposition. Moreover, key osteogenic markers of ALP activity, collagen type I (COL-1), osteopontin (OP), and osteocalcin (OCN) expression levels determined by real-time polymerase chain reaction (PCR) and immunofluorescence analysis were also significantly increased with the addition of glutamic acid residues to KLD. We demonstrated that the designed SAP scaffolds promoted the proliferation and osteogenic differentiation of hMSCs. Our results suggest that these designed bioactive peptide scaffolds may be useful for promoting bone tissue regeneration.

Laminin is the ECM niche for trophoblast stem cells

Laminin functions as an ECM niche factor for trophoblast stem cells and secures trophoblast stem cell expansion through its interactions with integrin.

The niche is a specialized microenvironment for tissue stem cells in vivo. It has long been emphasized that niche ECM molecules act on tissue stem cells to regulate their behavior, but the molecular entities of these interactions remain to be fully elucidated. Here, we report that laminin forms the in vivo ECM niche for trophoblast stem cells (TSCs), the tissue stem cells of the placenta. TSCs expressed fibronectin-binding, vitronectin-binding, and laminin-binding integrins, whereas the integrin ligands present in the TSC niche were collagen and laminin. Therefore, the only niche integrin ligand available for TSCs in vivo was laminin. Laminin promoted TSC adhesion and proliferation in vitro in an integrin binding–dependent manner. Importantly, when the integrin-binding ability of laminin was genetically ablated in mice, the size of the TSC population was significantly reduced compared with that in control mice. The present findings underscore an ECM niche function of laminin to support tissue stem cell maintenance in vivo.

Bipartite mechanism for laminin-integrin interactions: Identification of the integrin-binding site in LG domains of the laminin α chain

Laminins are major cell-adhesive proteins consisting of α, β, and γ chains, in which the three C-terminal globular domains of the α chain (LMα/LG1-3) and the C-terminal tail region of the γ1 chain (LMγ1-tail) are required for binding to integrin. Despite the recent progress on the role of LMγ1-tail in coordinating the metal ion-dependent adhesion site of the integrin β subunit, the mechanism by which LMα/LG1-3 interacts with integrin remains to be elucidated. We found that basic residues on the bottom face of LMα5/LG2 are required for binding laminin-511 to α6β1 integrin. Intermolecular cysteine scanning assays demonstrated that the basic residues in LMα5/LG2 were in contact with the acidic residues within the laminin-binding X1 region of the integrin α subunit in the laminin-integrin complex. These results indicate that LMα5/LG2 interacts directly with the integrin α subunit and comprises a bipartite integrin binding site of laminin-511 with the LMγ1-tail.

Structural biology of laminins

Laminins are large cell-adhesive glycoproteins that are required for the formation and function of basement membranes in all animals. Structural studies by electron microscopy in the early 1980s revealed a cross-shaped molecule, which subsequently was shown to consist of three distinct polypeptide chains. Crystallographic studies since the mid-1990s have added atomic detail to all parts of the laminin heterotrimer. The three short arms of the cross are made up of continuous arrays of disulphide-rich domains. The globular domains at the tips of the short arms mediate laminin polymerization; the surface regions involved in this process have been identified by structure-based mutagenesis. The long arm of the cross is an α-helical coiled coil of all three chains, terminating in a cell-adhesive globular region. The molecular basis of cell adhesion to laminins has been revealed by recent structures of heterotrimeric integrin-binding fragments and of a laminin fragment bound to the carbohydrate modification of dystroglycan. The structural characterization of the laminin molecule is essentially complete, but we still have to find ways of imaging native laminin polymers at molecular resolution.

Characterization of dystroglycan binding in adhesion of human induced pluripotent stem cells to laminin-511 E8 fragment

Human induced pluripotent stem cells (hiPSCs) grow indefinitely in culture and have the potential to regenerate various tissues. In the development of cell culture systems, a fragment of laminin-511 (LM511-E8) was found to improve the proliferation of stem cells. The adhesion of undifferentiated cells to LM511-E8 is mainly mediated through integrin α6β1. However, the involvement of non-integrin receptors remains unknown in stem cell culture using LM511-E8. Here, we show that dystroglycan (DG) is strongly expressed in hiPSCs. The fully glycosylated DG is functionally active for laminin binding, and although it has been suggested that LM511-E8 lacks DG binding sites, the fragment does weakly bind to DG. We further identified the DG binding sequence in LM511-E8, using synthetic peptides, of which, hE8A5-20 (human laminin α5 2688–2699: KTLPQLLAKLSI) derived from the laminin coiled-coil domain, exhibited DG binding affinity and cell adhesion activity. Deletion and mutation studies show that LLAKLSI is the active core sequence of hE8A5-20, and that, K2696 is a critical amino acid for DG binding. We further demonstrated that hiPSCs adhere to hE8A5-20-conjugated chitosan matrices. The amino acid sequence of DG binding peptides would be useful to design substrata for culture system of undifferentiated and differentiated stem cells.

Identification and quantification of sites of nitration and oxidation in the key matrix protein laminin and the structural consequences of these modifications

Laminin is a major protein of the basement membrane (BM), a specialized extracellular matrix (ECM) of the artery wall. The potent oxidizing and nitrating agent peroxynitrous acid (ONOOH) is formed at sites of inflammation, and data implicate ONOOH in ECM damage and cardiovascular disease. Co-localization of 3-nitrotyrosine, a product of ONOOH-mediated tyrosine (Tyr) modification, and laminin has been reported in human atherosclerotic lesions. The sites and consequences of 3-nitrotyrosine (and related nitrated tryptophan) formation on laminin, it's self-assembly and cell interactions are poorly understood. In this study murine laminin-111 was exposed to ONOOH (1–500-fold molar excess). Nitration sites were mapped and quantified using LC-MS/MS. Mono-nitration was detected at 148 sites (126 Tyr, 22 Trp), and di-nitration at 14 sites. Label-free quantification showed enhanced nitration with increasing oxidant doses. Tyr nitration was ∼10-fold greater than at Trp. CO₂ modulated damage in a site-specific manner, with most sites less extensively nitrated. 119 mono-nitration sites were identified with CO₂ present, and no unique sites were detected. 23 di-nitration sites were detected, with 15 unique to the presence of CO₂. Extensive modification was detected at sites involved in cell adhesion, protein-protein interactions and self-polymerization. Tyr-145 on the γ1 chain was extensively nitrated, and endothelial cells exhibited decreased adhesion to a nitrated peptide modelling this site. Modification of residues involved in self-polymerization interfered with the formation of ordered polymers as detected by scanning electron microscopy. These laminin modifications may contribute to endothelial cell dysfunction and modulate ECM structure and assembly, and thereby contribute to atherogenesis.

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Laminin is a major extracellular matrix protein of the artery wall.

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Peroxynitrous acid exposure gives nitration of tyrosine and tryptophan residues.

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CO₂ both increases and decreases damage depending of the reaction site.

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LC-MS/MS used to map modifications to protein structure and functional domains.

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Sites for cell adhesion, protein interactions and self-polymerization are modified.

Dynamic assembly of protein disulfide isomerase in catalysis of oxidative folding

Time-resolved direct observations of proteins in action provide essential mechanistic insights into biological processes. Here, we present mechanisms of action of protein disulfide isomerase (PDI)-the most versatile disulfide-introducing enzyme in the endoplasmic reticulum-during the catalysis of oxidative protein folding. Single-molecule analysis by high-speed atomic force microscopy revealed that oxidized PDI is in rapid equilibrium between open and closed conformations, whereas reduced PDI is maintained in the closed state. In the presence of unfolded substrates, oxidized PDI, but not reduced PDI, assembles to form a face-to-face dimer, creating a central hydrophobic cavity with multiple redox-active sites, where substrates are likely accommodated to undergo accelerated oxidative folding. Such PDI dimers are diverse in shape and have different lifetimes depending on substrates. To effectively guide proper oxidative protein folding, PDI regulates conformational dynamics and oligomeric states in accordance with its own redox state and the configurations or folding states of substrates.

Ventricular-subventricular zone fractones are speckled basement membranes that function as a neural stem cell niche

Neural stem cells (NSCs) are retained in the adult ventricular–subventricular zone (V-SVZ), a specialized neurogenic niche with a unique cellular architecture. It currently remains unclear whether or how NSCs utilize basement membranes (BMs) in this niche. Here, we examine the molecular compositions and functions of BMs in the adult mouse V-SVZ. Whole-mount V-SVZ immunostaining revealed that fractones, which are fingerlike processes of extravascular BMs, are speckled BMs unconnected to the vasculature, and differ in their molecular composition from vascular BMs. Glial fibrillary acidic protein (GFAP)-positive astrocytes and NSCs produce and adhere to speckled BMs. Furthermore, Gfap-Cre-mediated Lamc1^flox(E1605Q) knockin mice, in which integrin-binding activities of laminins are specifically nullified in GFAP-positive cells, exhibit a decreased number and size of speckled BMs and reduced in vitro neurosphere-forming activity. Our results reveal niche activities of fractones/speckled BMs for NSCs and provide molecular insights into how laminin–integrin interactions regulate NSCs in vivo.

Epidermolysis bullosa: Molecular pathology of connective tissue components in the cutaneous basement membrane zone

Epidermolysis bullosa (EB), a group of heritable skin fragility disorders, is characterized by blistering, erosions and chronic ulcers in the skin and mucous membranes. In some forms, the blistering phenotype is associated with extensive mutilating scarring and development of aggressive squamous cell carcinomas. The skin findings can be associated with extracutaneous manifestations in the ocular as well as gastrointestinal and vesico-urinary tracts. The phenotypic heterogeneity reflects the presence of mutations in as many as 20 different genes expressed in the cutaneous basement membrane zone, and the types and combinations of the mutations and their consequences at the mRNA and protein levels contribute to the spectrum of severity encountered in different subtypes of EB. This overview highlights the molecular genetics of EB based on mutations in the genes encoding type VII and XVII collagens as well as laminin-332. The mutations identified in these protein components of the extracellular matrix attest to their critical importance in providing stability to the cutaneous basement membrane zone, with implications for heritable and acquired diseases.

Laminin γ1 C-terminal Glu to Gln mutation induces early postimplantation lethality

Mouse embryos with an ablated ability of integrins to bind laminins are still able to form basement membranes, but die just after implantation because of deficient extraembryonic development.

Laminin–integrin interactions regulate various adhesion-dependent cellular processes. γ1C-Glu, the Glu residue in the laminin γ1 chain C-terminal tail, is crucial for the binding of γ1-laminins to several integrin isoforms. Here, we investigated the impact of γ1C Glu to Gln mutation on γ1-laminin binding to all possible integrin partners in vitro, and found that the mutation specifically ablated binding to α3, α6, and α7 integrins. To examine the physiological significance of γ1C-Glu, we generated a knock-in allele, Lamc1^EQ, in which the γ1C Glu to Gln mutation was introduced. Although Lamc1^EQ/EQ homozygotes developed into blastocysts and deposited laminins in their basement membranes, they died just after implantation because of disordered extraembryonic development. Given the impact of the Lamc1^EQ allele on embryonic development, we developed a knock-in mouse strain enabling on-demand introduction of the γ1C Glu to Gln mutation by the Cre-loxP system. The present study has revealed a crucial role of γ1C-Glu–mediated integrin binding in postimplantation development and provides useful animal models for investigating the physiological roles of laminin–integrin interactions in vivo.

Human CAP10-Like Protein 46 kDa Gene Promotes Malignancy in Colorectal Cancer

Colon cancer patients have major unmet needs in terms of robust diagnostics and molecular biomarkers for personalized therapeutics. We have previously reported that human CAP10-like protein 46 kDa (hCLP46) is overexpressed in human acute myelogenous leukemia, T acute lymphoblastic leukemia, and leukemia cell lines. We extend this line of biomarker and diagnostic discovery research by investigating hCLP46 expression in colorectal cancer (CRC) tissues and examine the possibility of hCLP46 as a candidate biomarker for diagnosis and prognosis of CRC. Using a tissue microarray analysis approach, we found that hCLP46 is (1) overexpressed in 90 CRC tissues compared with 90 matched noncancerous tissues and (2) positively correlated with higher tumor-node-metastasis (TNM) stage, lymph node metastasis, and shorter survival time. Moreover, in vitro experiments demonstrated that downregulation of hCLP46 in CRC cells results in proliferation arrest and adhesion enhancement, while apoptosis is unchanged. Further transcriptome profile analysis corroborated that the adhesion pathway is related to hCLP46 downregulation. This report for the first time, to the best of our knowledge, demonstrates that hCLP46 promotes tumor malignancy in CRC cells. We suggest that hCLP46 is warranted for further research as a candidate biomarker for clinical phenotypes related to colon cancer.

Laminin-deficient muscular dystrophy: Molecular pathogenesis and structural repair strategies

Laminins are large heterotrimers composed of the α, β and γ subunits with distinct tissue-specific and developmentally regulated expression patterns. The laminin-α2 subunit, encoded by the LAMA2 gene, is expressed in skeletal muscle, Schwann cells of the peripheral nerve and astrocytes and pericytes of the capillaries in the brain. Mutations in LAMA2 cause the most common type of congenital muscular dystrophies, called LAMA2 MD or MDC1A. The disorder manifests mostly as a muscular dystrophy but slowing of nerve conduction contributes to the disease. There are severe, non-ambulatory or milder, ambulatory variants, the latter resulting from reduced laminin-α2 expression and/or deficient laminin-α2 function. Lm-211 (α2β1γ1) is responsible for initiating basement membrane assembly. This is primarily accomplished by anchorage of Lm-211 to dystroglycan and α7β1 integrin receptors, polymerization, and binding to nidogen and other structural components. In LAMA2 MD, Lm-411 replaces Lm-211; however, Lm-411 lacks the ability to polymerize and bind to receptors. This results in a weakened basement membrane leading to the disease. The possibility of introducing structural repair proteins that correct the underlying abnormality is an attractive therapeutic goal. Recent studies in mouse models for LAMA2 MD reveal that introduction of laminin-binding linker proteins that restore lost functional activities can substantially ameliorate the disease. This review discusses the underlying mechanism of this repair and compares this approach to other developing therapies employing pharmacological treatments.

Mechanistic basis for the recognition of laminin-511 by α6β1 integrin

Laminins regulate diverse cellular functions through interaction with integrins. Two regions of laminins-three laminin globular domains of the α chain (LG1-3) and the carboxyl-terminal tail of the γ chain (γ-tail)-are required for integrin binding, but it remains unclear how the γ-tail contributes to the binding. We determined the crystal structure of the integrin binding fragment of laminin-511, showing that the γ-tail extends to the bottom face of LG1-3. Electron microscopic imaging combined with biochemical analyses showed that integrin binds to the bottom face of LG1-3 with the γ1-tail apposed to the metal ion-dependent adhesion site (MIDAS) of integrin β1. These findings are consistent with a model in which the γ-tail coordinates the metal ion in the MIDAS through its Glu residue.

Fibrin functionalization with synthetic adhesive ligands interacting with α6β1 integrin receptor enhance neurite outgrowth of embryonic stem cell-derived neural stem/progenitors

To enhance fibrin hydrogel affinity towards pluripotent stem cell-derived neural stem/progenitor cells (NSPCs) and its capacity to support NSPC migration and neurite extension, we explored the tethering of synthetic peptides engaging integrin α6β1, a cell receptor enriched in NSPCs. Six α6β1 integrin ligands were tested for their ability to support integrin α6β1-mediated adhesion of embryonic stem cell-derived NSPCs (ES-NSPs) and sustain ES-NSPC viability, migration, and neuronal differentiation. Due to their better performance, peptides T1, HYD1, and A5G81 were immobilized into fibrin and functionalized gels characterized in terms of peptide binding efficiency, structure and viscoelastic properties. Tethering of T1 or HYD1 successfully enhanced cell outgrowth from ES-NSPC neurospheres (up to 2.4-fold increase), which exhibited a biphasic response to peptide concentration. Inhibition assays evidenced the involvement of α6β1 and α3β1 integrins in mediating radial outgrowth on T1-/HYD1-functionalized gels. Fibrin functionalization also promoted neurite extension of single ES-NSPCs in fibrin, without affecting cell proliferation and neuronal differentiation. Finally, HYD1-functionalized gels were found to provide a permissive environment for axonal regeneration, leading up to a 2.0-fold increase in neurite extension from rat dorsal root ganglia explants as compared to unmodified fibrin, and to significant improved locomotor function after spinal cord injury (complete transection), along with a trend toward a higher area positive for growth associated protein 43 (marker for axonal growth cone formation). Our results suggest that conjugation of α6β1 integrin-binding motifs is of interest to increase the biofunctionality of hydrogels used in 3D platforms for ES-NSPC culture and potentially, in matrix-assisted ES-NSPC transplantation.

STATEMENT OF SIGNIFICANCE

Impact statement: The transplantation of NSPCs derived from pluripotent stem cells holds much promise for the treatment of central nervous system disorders. Moreover, the combinatorial use of biodegradable hydrogels with NSPCs was shown to contribute to the establishment of a more permissive environment for survival and integration of transplanted cells. In this study, fibrin hydrogels functionalized with a synthetic peptide engaging integrin α6β1 (HYD1) were shown to promote neurite extension of ES-NSPCs, which is fundamental for the formation of functional neuronal relay circuits after NSPC transplantation. Notably, HYD1-functionalized fibrin per se led to enhanced axonal growth ex vivo and to an improvement in locomotor function after implantation in a rat model of spinal cord injury. Conjugation of α6β1 integrin-binding motifs may therefore be of interest to confer bioactivity to NSPC hydrogel vehicles.

Recombinant laminin fragments endowed with collagen-binding activity: A tool for conferring laminin-like cell-adhesive activity to collagen matrices

Laminins are major components of basement membranes that sustain a wide variety of stem cells. Among 15 laminin isoforms, laminin-511 and its E8 fragment (LM511E8) have been shown to strongly promote the adhesion and proliferation of human pluripotent stem cells. The aim of this study was to endow the cell-adhesive activity of laminin-511 on collagen matrices, thereby fabricating collagen-based culture scaffolds for stem cells with defined composition. To achieve this goal, we utilized the collagen-binding domain (CBD) of fibronectin to immobilize LM511E8 on collagen matrices. CBD was attached to the N-termini of individual laminin chains (α5E8, β1E8, γ1E8), producing LM511E8s having one, two, or three CBDs. While LM511E8 did not bind to collagen, CBD-attached LM511E8s (CBD-LM511E8s) exhibited significant collagen-binding activity, dependent on the number of attached CBDs. Human iPS cells were cultured on collagen-coated plates preloaded with CBD-LM511E8s. Although iPS cells did not attach or grow on collagen, they robustly proliferated on CBD-LM511E8-loaded collagen matrices, similar to the case with LM511E8-coated plates. Importantly, iPS cells proliferated and yielded round-shaped colonies even on collagen gels preloaded with CBD-LM511E8s. These results demonstrate that CBD-attached laminin E8 fragments are promising tools for fabrication of collagen-based matrices having the cell-adhesive activity of laminins.

Probing the acidic residue within the integrin binding site of laminin-511 that interacts with the metal ion-dependent adhesion site of α6β1 integrin

Laminins are major cell-adhesive proteins of basement membranes that interact with integrins in a divalent cation-dependent manner. Laminin-511 consists of α5, β1, and γ1 chains, of which three laminin globular domains of the α5 chain (α5/LG1-3) and a Glu residue in the C-terminal tail of chain γ1 (γ1-Glu1607) are required for binding to integrins. However, it remains unsettled whether the Glu residue in the γ1 tail is involved in integrin binding by coordinating the metal ion in the metal ion-dependent adhesion site of β1 integrin (β1-MIDAS), or by stabilizing the conformation of α5/LG1-3. To address this issue, we examined whether α5/LG1-3 contain an acidic residue required for integrin binding that is as critical as the Glu residue in the γ1 tail; to achieve this, we undertook exhaustive alanine substitutions of the 54 acidic residues present in α5/LG1-3 of the E8 fragment of laminin-511 (LM511E8). Most of the alanine mutants possessed α6β1 integrin binding activities comparable with wild-type LM511E8. Alanine substitution for α5-Asp3198 and Asp3219 caused mild reduction in integrin binding activity, and that for α5-Asp3218 caused severe reduction, possibly resulting from conformational perturbation of α5/LG1-3. When α5-Asp3218 was substituted with asparagine, the resulting mutant possessed significant binding activity to α6β1 integrin, indicating that α5-Asp3218 is not directly involved in integrin binding through coordination with the metal ion in β1-MIDAS. Given that substitution of γ1-Glu1607 with glutamine nullified the binding activity to α6β1 integrin, these results, taken together, support the possibility that the critical acidic residue coordinating the metal ion in β1-MIDAS is Glu1607 in the γ1 tail, but no such residue is present in α5/LG1-3.

Crystal Structure of the Heterotrimeric Integrin-Binding Region of Laminin-111

Laminins are cell-adhesive glycoproteins that are essential for basement membrane assembly and function. Integrins are important laminin receptors, but their binding site on the heterotrimeric laminins is poorly defined structurally. We report the crystal structure at 2.13 Å resolution of a minimal integrin-binding fragment of mouse laminin-111, consisting of ∼50 residues of α1β1γ1 coiled coil and the first three laminin G-like (LG) domains of the α1 chain. The LG domains adopt a triangular arrangement, with the C terminus of the coiled coil situated between LG1 and LG2. The critical integrin-binding glutamic acid residue in the γ1 chain tail is surface exposed and predicted to bind to the metal ion-dependent adhesion site in the integrin β1 subunit. Additional contacts to the integrin are likely to be made by the LG1 and LG2 surfaces adjacent to the γ1 chain tail, which are notably conserved and free of obstructing glycans.

Fundamentals of protein and cell interactions in biomaterials

The extracellular matrix (ECM) is an active and complex microenvironment with outstanding biomechanical, biophysical, and biochemical characteristics, which can indirectly or directly controls cell adhesion, migration, proliferation, and differentiation, as well as partaking in regeneration and homeostasis of organs and tissues. The ECM has captivated a great deal of attention with the rapid progress of tissue engineering (TE) in the field of regenerative medicine (RM). Approaches to TE, RM and cancer therapy center on the necessity to deliver cell signals to direct cell proliferation and differentiation. These "external signals" are induced from cell-cell, and cell-ECM, interactions, as well as from physico-chemical, mechanical stimuli and growth factors. With the advent of new biomaterials such as casein, we gave a general insight into cell-ECM protein interactions in biomaterials and their applications in TE, RM and cancer therapy. An account of the main ECM molecules and cellular receptors with emphasis on integrins and its ligands was given, their effect on the induction of particular signal transduction pathways is also elucidated.

Cross-linking reveals laminin coiled-coil architecture

Laminin, an ∼800-kDa heterotrimeric protein, is a major functional component of the extracellular matrix, contributing to tissue development and maintenance. The unique architecture of laminin is not currently amenable to determination at high resolution, as its flexible and narrow segments complicate both crystallization and single-particle reconstruction by electron microscopy. Therefore, we used cross-linking and MS, evaluated using computational methods, to address key questions regarding laminin quaternary structure. This approach was particularly well suited to the ∼750-Å coiled coil that mediates trimer assembly, and our results support revision of the subunit order typically presented in laminin schematics. Furthermore, information on the subunit register in the coiled coil and cross-links to downstream domains provide insights into the self-assembly required for interaction with other extracellular matrix and cell surface proteins.

Laminin 411 and 511 promote the cholangiocyte differentiation of human induced pluripotent stem cells

The drug discovery research for cholestatic liver diseases has been hampered by the lack of a well-established human cholangiocyte model. Functional cholangiocyte-like cells differentiated from human induced pluripotent stem (iPS) cells are expected to be a promising candidate for such research, but there remains no well-established method for differentiating cholangiocytes from human iPS cells. In this study, we searched for a suitable extracellular matrix to promote cholangiocyte differentiation from human iPS cells, and found that both laminin 411 and laminin 511 were suitable for this purpose. The gene expression levels of the cholangiocyte markers, aquaporin 1 (AQP1), SRY-box 9 (SOX9), cystic fibrosis transmembrane conductance regulator (CFTR), G protein-coupled bile acid receptor 1 (GPBAR1), Jagged 1 (JAG1), secretin receptor (SCTR), and γ-glutamyl transferase (GGT1) were increased by using laminin 411 or laminin 511 as a matrix. In addition, the percentage of AQP1-positive cells was increased from 61.8% to 92.5% by using laminin 411 or laminin 511. Furthermore, the diameter and number of cysts consisted of cholangiocyte-like cells were increased when using either matrix. We believe that the human iPS cell-derived cholangiocyte-like cells, which were generated by using our differentiation technology, would be useful for the drug discovery research of cholestatic liver diseases.

Molecular Basis of the Ligand Binding Specificity of αvβ8 Integrin

αvβ8 is an integrin that recognizes an Arg-Gly-Asp (RGD) motif and interacts with fibronectin, vitronectin, and latent TGF-β1. We comprehensively determined the binding activity of the αvβ8 integrin toward 25 secreted proteins having an RGD motif. The αvβ8 integrin strongly bound to latent TGF-β1 but showed marginal activity for other RGD-containing proteins, including fibronectin and vitronectin. Site-directed mutagenesis of latent TGF-β1 demonstrated that the high affinity binding of αvβ8 integrin to latent TGF-β1 was defined by Leu-218 immediately following the RGD motif within the latency-associated peptide of TGF-β1. Consistent with the critical role of Leu-218 in latent TGF-β1 recognition by αvβ8 integrin, a 9-mer synthetic peptide containing an RGDL sequence strongly inhibited interactions of latent TGF-β1 with αvβ8 integrin, whereas a 9-mer peptide with an RGDA sequence was ∼60-fold less inhibitory. Because αvβ3 integrin did not exhibit strong binding to latent TGF-β1 or distinguish between RGDL- and RGDA-containing peptides, we explored the mechanism by which the integrin β8 subunit defines the high affinity binding of latent TGF-β1 by αvβ8 integrin. Production of a series of swap mutants of integrin β8 and β3 subunits indicated that the high affinity binding of αvβ8 integrin with latent TGF-β1 was ensured by interactions between the Leu-218 residue and the β8 I-like domain, with the former serving as an auxiliary recognition residue defining the restricted ligand specificity of αvβ8 integrin toward latent TGF-β1. In support of this conclusion, high affinity binding toward the αvβ8 integrin was conferred on fibronectin by substitution of its RGDS motif with an RGDL sequence.

A dystonia-like movement disorder with brain and spinal neuronal defects is caused by mutation of the mouse laminin β1 subunit, Lamb1

A new mutant mouse (lamb1t) exhibits intermittent dystonic hindlimb movements and postures when awake, and hyperextension when asleep. Experiments showed co-contraction of opposing muscle groups, and indicated that symptoms depended on the interaction of brain and spinal cord. SNP mapping and exome sequencing identified the dominant causative mutation in the Lamb1 gene. Laminins are extracellular matrix proteins, widely expressed but also known to be important in synapse structure and plasticity. In accordance, awake recording in the cerebellum detected abnormal output from a circuit of two Lamb1-expressing neurons, Purkinje cells and their deep cerebellar nucleus targets, during abnormal postures. We propose that dystonia-like symptoms result from lapses in descending inhibition, exposing excess activity in intrinsic spinal circuits that coordinate muscles. The mouse is a new model for testing how dysfunction in the CNS causes specific abnormal movements and postures.

Molecular Basis of Laminin-Integrin Interactions

Laminins are composed of three polypeptide chains, designated as α, β, and γ. The C-terminal region of laminin heterotrimers, containing coiled-coil regions, short tails, and laminin globular (LG) domains, is necessary and sufficient for binding to integrins, which are the major laminin receptor class. Laminin recognition by integrins critically requires the α chain LG domains and a glutamic acid residue of the γ chain at the third position from the C-terminus. Furthermore, the C-terminal region of the β chain contains a short amino acid sequence that modulates laminin affinity for integrins. Thus, all three of the laminin chains act cooperatively to facilitate integrin binding. Mammals possess 5 α (α1-5), 3 β (β1-3), and 3 γ (γ1-3) chains, combinations of which give rise to 16 distinct laminin isoforms. Each isoform is expressed in a tissue-specific and developmental stage-specific manner, exerting its functions through binding of integrins. In this review, we detail the current knowledge surrounding the molecular basis and physiological relevance of specific interactions between laminins and integrins, and describe the mechanisms underlying laminin action through integrins.

Integrating Activities of Laminins that Drive Basement Membrane Assembly and Function

Studies on extracellular matrix proteins, cells, and genetically modified animals have converged to reveal mechanisms of basement membrane self-assembly as mediated by γ1 subunit-containing laminins, the focus of this chapter. The basic model is as follows: A member of the laminin family adheres to a competent cell surface and typically polymerizes followed by laminin binding to the extracellular adaptor proteins nidogen, perlecan, and agrin. Assembly is completed by the linking of nidogen and heparan sulfates to type IV collagen, allowing it to form a second stabilizing network polymer. The assembled matrix provides structural support, anchoring the extracellular matrix to the cytoskeleton, and acts as a signaling platform. Heterogeneity of function is created in part by the isoforms of laminin that vary in their ability to polymerize and to interact with integrins, dystroglycan, and other receptors. Mutations in laminin subunits, affecting expression or LN domain-specific functions, are a cause of human diseases that include those of muscle, nerve, brain, and kidney.

Novel ENAM and LAMB3 mutations in Chinese families with hypoplastic amelogenesis imperfecta

Amelogenesis imperfecta is a group of inherited diseases affecting the quality and quantity of dental enamel. To date, mutations in more than ten genes have been associated with non-syndromic amelogenesis imperfecta (AI). Among these, ENAM and LAMB3 mutations are known to be parts of the etiology of hypoplastic AI in human cases. When both alleles of LAMB3 are defective, it could cause junctional epidermolysis bullosa (JEB), while with only one mutant allele in the C-terminus of LAMB3, it could result in severe hypoplastic AI without skin fragility. We enrolled three Chinese families with hypoplastic autosomal-dominant AI. Despite the diagnosis falling into the same type, the characteristics of their enamel hypoplasia were different. Screening of ENAM and LAMB3 genes was performed by direct sequencing of genomic DNA from blood samples. Disease-causing mutations were identified and perfectly segregated with the enamel defects in three families: a 19-bp insertion mutation in the exon 7 of ENAM (c.406_407insTCAAAAAAGCCGACCACAA, p.K136Ifs*16) in Family 1, a single-base deletion mutation in the exon 5 of ENAM (c. 139delA, p. M47Cfs*11) in Family 2, and a LAMB3 nonsense mutation in the last exon (c.3466C>T, p.Q1156X) in Family 3. Our results suggest that heterozygous mutations in ENAM and LAMB3 genes can cause hypoplastic AI with markedly different phenotypes in Chinese patients. And these findings extend the mutation spectrum of both genes and can be used for mutation screening of AI in the Chinese population.

Laminin-α2 Chain-Deficient Congenital Muscular Dystrophy: Pathophysiology and Development of Treatment

Laminin-211 is a major constituent of the skeletal muscle basement membrane. It stabilizes skeletal muscle and influences signal transduction events from the myomatrix to the muscle cell. Mutations in the gene encoding the α2 chain of laminin-211 lead to congenital muscular dystrophy type 1A (MDC1A), a life-threatening disease characterized by severe hypotonia, progressive muscle weakness, and joint contractures. Common complications include severely impaired motor ability, respiratory failure, and feeding difficulties. Several adequate animal models for laminin-α2 chain deficiency exist and analyses of different MDC1A mouse models have led to a significant improvement in our understanding of MDC1A pathogenesis. Importantly, the animal models have been indispensable tools for the preclinical development of new therapeutic approaches for laminin-α2 chain deficiency, highlighting a number of important disease driving mechanisms that can be targeted by pharmacological approaches. In this chapter, I will describe laminin-211 and discuss the cellular and molecular pathophysiology of MDC1A as well as progression toward development of treatment.

Screening of integrin-binding peptides in a laminin peptide library derived from the mouse laminin β chain short arm regions

Laminins, major components of basement membrane, consist of three different subunits, α, β, and γ chains, and so far, five α, three β, and three γ chains have been identified. We have constructed synthetic peptide libraries derived from the laminin sequences and identified various cell-adhesive peptides. Ten active peptides from the laminin α chain sequences (α1-α5) were found to promote integrin-mediated cell adhesion. Previously, we found fourteen cell-adhesive peptides from the β1 chain sequence but their receptors have not been analyzed. Here, we expanded the synthetic peptide library to add peptides from the short arm regions of the laminin β2 and β3 chains and screened for integrin-binding peptides. Twenty-seven peptides promoted human dermal fibroblast (HDF) attachment in a peptide-coated plate assay. The morphological appearance of HDFs on the peptide-coated plates differed depending on the peptides. B34 (REKYYYAVYDMV, mouse laminin β1 chain, 255-266), B67 (IPYSMEYEILIRY, mouse laminin β1 chain, 604-616), B2-105 (APNFWNFTSGRG, mouse laminin β2 chain, 1081-1092), and B3-19 (GHLTGGKVQLNL, mouse laminin β3 chain, 182-193) promoted HDF spreading and HDF attachment was inhibited by EDTA, suggesting that the peptides interact with integrins. Immunostaining analyses revealed that B67 induced well-organized actin stress fibers and focal contacts containing vinculin, however, B34, B2-105, and B3-19 did not exhibit stress fiber formation or focal contacts. The inhibition assay using anti-integrin antibodies indicated that B67 interacts with α3, α6, and β1 integrins, and B34 and B3-19 interact with β1 integrin. Based on adhesion analysis of peptides modified with an alanine scan and on switching analysis with the homologous inactive sequence B2-64 (LPRAMDYDLLLRW, mouse laminin β2 chain, 618-630), the Glu(8) residue in the B67 peptide was critical for HDF adhesion. These findings are useful for identifying an integrin binding motif. The B67 peptide has potential for use as a molecular probe for integrins.

Alumina-zirconia composites functionalized with laminin-1 and laminin-5 for dentistry: effect of protein adsorption on cellular response

The present paper describes a study on laminin interaction with the surface of two alumina-zirconia composites with different percentages of ZrO2, both with submicrometric grain size. As major molecules within the basement membrane (BM), laminins are important protein fragments for epithelial cell adhesion and migration. On the other hand, alumina-zirconia composites are very attractive materials for dental applications due to their esthetic and mechanical properties. X-Ray photoelectron spectroscopy and atomic force microscopy were used to study the adsorption of two types of laminin, laminin-1 (Ln-1) and laminin-5 (Ln-5), onto the ceramics surfaces. The in vitro cell response was determined by intracellular phosphorylation of major kinases. Ceramics samples functionalized with laminins showed better cellular activation than untreated specimens; furthermore, cellular activation was found to be greater for the composite with higher percentage in zirconia when functionalized with Ln-5, whereas the adsorption of Ln-1 resulted in a greater activation for the alumina-rich oxide.

A novel efficient feeder-free culture system for the derivation of human induced pluripotent stem cells

In order to apply human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) to regenerative medicine, the cells should be produced under restricted conditions conforming to GMP guidelines. Since the conventional culture system has some issues that need to be addressed to achieve this goal, we developed a novel culture system. We found that recombinant laminin-511 E8 fragments are useful matrices for maintaining hESCs and hiPSCs when used in combination with a completely xeno-free (Xf) medium, StemFit™. Using this system, hESCs and hiPSCs can be easily and stably passaged by dissociating the cells into single cells for long periods, without any karyotype abnormalities. Human iPSCs could be generated under feeder-free (Ff) and Xf culture systems from human primary fibroblasts and blood cells, and they possessed differentiation abilities. These results indicate that hiPSCs can be generated and maintained under this novel Ff and Xf culture system.

Ex vivo pathogenicity of anti-laminin γ1 autoantibodies

Autoimmunity against laminins has been described in several autoimmune diseases (including mucous membrane pemphigoid, anti-laminin γ1 pemphigoid, and connective tissue diseases), in pregnancy loss, and in infections such as Chagas disease. Except for anti-laminin-332 mucous membrane pemphigoid, adequate evidence has been lacking for the tissue injury potential of laminin-specific antibodies and the pathogenic epitopes. We evaluated the pathogenic potential of antibodies targeting laminin γ1, a major constituent of basement membranes and the main antigen in anti-laminin γ1 pemphigoid. Rabbit antibodies were generated against fragments of the N-terminus and C-terminus of murine laminin γ1, and their ability to disrupt ligand interactions and/or to activate complement and granulocytes was assessed using previously established ex vivo assays. Our findings document a pathogenic potential of antibodies targeting the laminin γ1 N-terminus. These antibodies interfere with the binding of nidogen to laminin and can activate granulocytes and the complement cascade. We detected antibodies with different degrees of reactivity with laminin γ1 N-terminus in patients with anti-laminin γ1 pemphigoid, cutaneous lupus erythematosus, and scleroderma. Our results provide mechanistic insights into the tissue damage associated with laminin autoimmunity and could facilitate development of appropriate diagnostic tools and therapeutic strategies.

Prostate specific membrane antigen produces pro-angiogenic laminin peptides downstream of matrix metalloprotease-2

Prostate specific membrane antigen (PSMA) is a pro-angiogenic cell-surface protease that we previously demonstrated regulates blood vessel formation in a laminin and integrin β1-dependent manner. Here, we examine the principal mechanism of PSMA activation of integrin β1. We show that digesting laminin sequentially with recombinant matrix metalloprotease-2 (MMP-2) and PSMA generates small peptides that enhance endothelial cell adhesion and migration in vitro. We also provide evidence that these laminin peptides activate adhesion via integrin α6β1 and focal adhesion kinase. Using an in vivo Matrigel implant assay, we show that these MMP/PSMA-derived laminin peptides also increase angiogenesis in vivo. Together, our results reveal a novel mechanism of PSMA activation of angiogenesis by processing laminin downstream of MMP-2.