Microfibril-associated Glycoproteins Research Articles

Therapeutic Effect of Nile Tilapia Type II Collagen on Rigidity in CD8+ Cells by Alleviating Inflammation and Rheumatoid Arthritis in Rats by Oral Tolerance.

Fibrillins are microfibril-associated macro glycoproteins found in connective tissues and structurally related to latent TGF-β-binding proteins (LTBPs). The special cellular immunity and blocking glycoprotein receptors IIb and IIIa of fibrillins are emerging topics in recent years. In this study, Nile Tilapia type IIcollagen (NTCII) was extracted and purified from the skull cartilages by a pepsin-soluble method. Amino acid analysis indicated that NTCII consisted of 315/1000 glycine residues, 72/1000 hydroxyproline residues and 108/1000 proline residues. SDS-PAGE analysis showed that NTCII was composed of three identical 130 kDa α-chains. The results of glycoprotein/carbohydrate assay indicated that the total polysaccharide content of NTCII was 5.6–19.0%. The IR spectrum of NTCII displayed five characteristic peaks of amide I, II, III, A, B. NTCII at 10–100 μg/mL concentration downregulated the content of cytokines in the presence or absence of LPS, especially the secretion of cytokines IL-6, IL-1β and TNF-α. Interestingly, NTCII promoted the secretion of Fas/Apo-1 compared to the control group and 25 μg/mL of NTCII resulted in a higher Fas/Apo-1 secretion level in CD8+ T cells. FITC-TCII fluorescence images confirmed that NTCII could bind to the membrane surface of CD8+ T cells, leading to the induction of rigidity. NTCII could bind to the membrane surface of CD8+ T cells that leads to the induction of rigidity, as evidenced by the FITC-NTCII fluorescence images. The qRT-PCR gene expression analysis of caspase-8 collected with Fas/Apo-1 was upregulated significantly in the 1 and 50 μg/mL NTCII-treated groups compared with the control group. Overall, the results conclude that the rigidity did not lead to an increase in inflammatory factors in CD8+ T cells treated with NTCII. The oral administration of NTCII 3 mg/kg dosage caused more prominent repair of damaged ankle cartilage than the 1 mg/kg dosage in Freund’s adjuvant-induced model of arthritis in rats. Therefore, this study disclosed the immunological and anti-arthritic effect of fibrillar collagen, which could be a potential biomaterial for practical applications with lower toxicity.

Human Microfibrillar-Associated Protein 4 (MFAP4) Gene Promoter: A TATA-Less Promoter That Is Regulated by Retinol and Coenzyme Q10 in Human Fibroblast Cells.

Elastic fibers are one of the major structural components of the extracellular matrix (ECM) in human connective tissues. Among these fibers, microfibrillar-associated protein 4 (MFAP4) is one of the most important microfibril-associated glycoproteins. MFAP4 has been found to bind with elastin microfibrils and interact directly with fibrillin-1, and then aid in elastic fiber formation. However, the regulations of the human MFAP4 gene are not so clear. Therefore, in this study, we firstly aimed to analyze and identify the promoter region of the human MFAP4 gene. The results indicate that the human MFAP4 promoter is a TATA-less promoter with tissue- and species-specific properties. Moreover, the promoter can be up-regulated by retinol and coenzyme Q10 (coQ10) in Detroit 551 cells.

EMILIN proteins are novel extracellular constituents of the dentin-pulp complex

Odontoblasts and pulp stroma cells are embedded within supramolecular networks of extracellular matrix (ECM). Fibrillin microfibrils and associated proteins are crucial constituents of these networks, serving as contextual scaffolds to regulate tissue development and homeostasis by providing both structural and mechanical properties and sequestering growth factors of the TGF-β superfamily. EMILIN-1, -2, and -3 are microfibril-associated glycoproteins known to modulate cell behaviour, growth factor activity, and ECM assembly. So far their expression in the various cells of the dentin-pulp complex during development, in the adult stage, and during inflammation has not been investigated. Confocal immunofluorescence microscopy and western blot analysis of developing and adult mouse molars and incisors revealed an abundant presence of EMILINs in the entire dental papilla, at early developmental stages. Later in development the signal intensity for EMILIN-3 decreases, while EMILIN-1 and -2 staining appears to increase in the pre-dentin and in the ECM surrounding odontoblasts. Our data also demonstrate new specific interactions of EMILINs with fibulins in the dentin enamel junction. Interestingly, in dentin caries lesions the signal for EMILIN-3 was significantly increased in inflamed odontoblasts. Overall our findings point for the first time to a role of EMILINs in dentinogenesis, pulp biology, and inflammation.

Elastin structure and its involvement in skin photoageing

Skin aging is a complex process that may be caused by factors that are intrinsic and extrinsic to the body. Ultraviolet (UV) radiation represents one of the main sources of skin damage over the years and characterizes a process known as photoaging. Among the changes that affect cutaneous tissue with age, the loss of elastic properties caused by changes in elastin production, increased degradation and/or processing produces a substantial impact on tissue esthetics and health. The occurrence of solar elastosis is one of the main markers of cutaneous photoaging and is characterized by disorganized and non-functional deposition of elastic fibers. The occurrence of UV radiation-induced alternative splicing of the elastin gene, which leads to inadequate synthesis of the proteins required for the correct assembly of elastic fibers, is a potential explanation for this phenomenon. Innovative studies have been fundamental for the elucidation of rarely explored photoaging mechanisms and have enabled the identification of effective therapeutic alternatives such as cosmetic products. This review addresses cutaneous photoaging and the changes that affect elastin in this process.

The extracellular matrix protein MAGP1 is a key regulator of adipose tissue remodeling during obesity.

In response to increases in fat mass, as seen in obesity, the adipose tissue undergoes distinct structural remodeling (1). Recent attention has focused on the importance of the extracellular matrix (ECM) in remodeling of adipose tissue during the development of obesity. The ECM not only provides structural support to the surrounding cells, but also plays a crucial role in the biological function of different organs. Components of the ECM include structural proteins, such as collagen and fibrillins, and various classes of adhesion proteins, such as fibronectin and proteoglycan. Fibrillins are large proteins that form extracellular microfibril suprastructures ubiquitously found in elastic and nonelastic tissues. Constitutive components of the microfibrils also include the microfibril-associated glycoproteins (MAGPs) 1 and 2 (2,3). Microfibrils appear to have dual roles: They confer mechanical stability and limited elasticity to tissues and modulate the activity of members of the transforming growth factor-β (TGF-β) superfamily (4–6). The importance of microfibrils in regulating TGF-β activity is illustrated by the phenotype associated …

Functional evolution of the microfibril-associated glycoproteins

The microfibril-associated glycoproteins (MAGPs) are cysteine-rich low molecular weight components of the fibrillin-based microfibrillar complex. MAGPs are evolutionarily conserved in vertebrates and have important roles in microfibril and elastic fiber structure, homeostasis, and vascular development. Two MAGPs, designated MAGP1 and MAGP2, are encoded in the mammalian genome. Although MAGP sequences have been identified in several vertebrate species, the extent of conservation and evolutionary history of the MAGPs in vertebrates is unknown. Sequence similarity searches of nucleotide and protein databases identified the first homologs of MAGP1 in monotremes, birds, elasmobranchs and agnathans, and the first MAGP2 genes in marsupials, birds and teleosts. A model for MAGP evolution is presented. Phylogenetic analysis identified the ancient origin of MAGP1 and the evolution of MAGP2 from a gene duplication event early in vertebrate evolution. Phylogenomic analysis shows conservation of synteny between teleosts and tetrapods and suggests a multigene duplication event. The MAGP2 gene has evolved rapidly as an innovation in the bony vertebrate lineage. Estimates of functional divergence and complex nucleotide substitution models suggest that the divergence of MAGP2 took place by relaxation of selective constraints; and that MAGP1 has consistently been constrained by strong purifying selection. Correlated evolution between MAGP1 and the developmental regulator, Notch1, may explain some of the selective forces acting on MAGP2.

Marfan syndrome and its disorder in periodontal tissues

Elastic system fibers are composed of two distinct elements, elastin, which is an amorphous component crosslinked in the core, and microfibril, localized in the periphery of elastin. As microfibrillar proteins, fibrillins, microfibril-associated glycoproteins (MAGPs), latent TGF-beta-binding proteins (LTBPs), microfibril-associated proteins (MFAPs), and fibulins are known. Fibrillin-1 is a major microfibrillar protein and characterized by calcium binding EGF-like (cbEGF) domain. Association between fibrillin-1 and TGF-beta is a recent topic of this field and this interaction is known to inactivate and target TGF-beta action. FBN1 encoding fibrillin-1 is a responsible gene for Marfan syndrome type 1 (MIM #154700), characterized by increased height and long limbs, ectopia lentis, and cardiovascular disorders, such as mitral valve prolapse and aortic dilation and regurgitation. Animal models suggest that the abnormal TGF-beta signaling is underlying as the pathogenesis of these conditions. Besides skeletal, ocular and cardiovascular conditions, severe periodontitis is frequently seen in affected patients. To clarify the unknown function of elastic system fibers in the periodontal ligament (PDL), PDL-cells were isolated from a Marfan syndrome type 1 patient who was with the severe periodontitis and had a mutation in one of the cbEGF domain of fibrillin-1. These results suggested that wild-type fibrillin-1 was required for the normal cell alignment and tissue architecture of PDLs. Evidences are now accumulated to suggest that fibrillin-1 is one of the molecule involved in the interaction between cell and extracellular matrix.

New insights into elastic fiber assembly

Elastic fibers provide recoil to tissues that undergo repeated stretch, such as the large arteries and lung. These large extracellular matrix (ECM) structures contain numerous components, and our understanding of elastic fiber assembly is changing as we learn more about the various molecules associated with the assembly process. The main components of elastic fibers are elastin and microfibrils. Elastin makes up the bulk of the mature fiber and is encoded by a single gene. Microfibrils consist mainly of fibrillin, but also contain or associate with proteins such as microfibril associated glycoproteins (MAGPs), fibulins, and EMILIN-1. Microfibrils were thought to facilitate alignment of elastin monomers prior to cross-linking by lysyl oxidase (LOX). We now know that their role, as well as the overall assembly process, is more complex. Elastic fiber formation involves elaborate spatial and temporal regulation of all of the involved proteins and is difficult to recapitulate in adult tissues. This report summarizes the known interactions between elastin and the microfibrillar proteins and their role in elastic fiber assembly based on in vitro studies and evidence from knockout mice. We also propose a model of elastic fiber assembly based on the current data that incorporates interactions between elastin, LOXs, fibulins and the microfibril, as well as the pivotal role played by cells in structuring the final functional fiber.

Proteoglycans and pathophysiology

ventilation-induced lung injury (VILI) is an important clinical entity whose pathophysiology is incompletely understood. The article by Moriondo and coworkers ([14][1]) in the Journal of Applied Physiology offers new insights into potential mechanistic pathways. These authors report that one of the

Latent TGF-β-binding protein 2 binds to DANCE/fibulin-5 and regulates elastic fiber assembly

Elastic fibers play the principal roles in providing elasticity and integrity to various types of human organs, such as the arteries, lung, and skin. However, the molecular mechanism of elastic fiber assembly that leads to deposition and crosslinking of elastin along microfibrils remains largely unknown. We have previously shown that developing arteries and neural crest EGF-like protein (DANCE) (also designated fibulin-5) is essential for elastogenesis by studying DANCE-deficient mice. Here, we report the identification of latent transforming growth factor-beta-binding protein 2 (LTBP-2), an elastic fiber-associating protein whose function in elastogenesis is not clear, as a DANCE-binding protein. Elastogenesis assays using human skin fibroblasts reveal that fibrillar deposition of DANCE and elastin is largely dependent on fibrillin-1 microfibrils. However, downregulation of LTBP-2 induces fibrillin-1-independent fibrillar deposition of DANCE and elastin. Moreover, recombinant LTBP-2 promotes deposition of DANCE onto fibrillin-1 microfibrils. These results suggest a novel regulatory mechanism of elastic fiber assembly in which LTBP-2 regulates targeting of DANCE on suitable microfibrils to form elastic fibers.

Microfibril-associated MAGP-2 Stimulates Elastic Fiber Assembly

Elastic fibers are complex structures composed of a tropoelastin inner core and microfibril outer mantle guiding tropoelastin deposition. Microfibrillar proteins mainly include fibrillins and microfibril-associated glycoproteins (MAGPs). MAGP-2 exhibits developmental expression peaking at elastic fiber onset, suggesting that MAGP-2 mediates elastic fiber assembly. To determine whether MAGP-2 regulates elastic fiber assembly, we used an in vitro model featuring doxycycline-regulated cells conditionally overexpressing exogenous MAGP-2 and constitutively expressing enhanced green fluorescent protein-tagged tropoelastin. Analysis by immunofluorescent staining showed that MAGP-2 overexpression dramatically increased elastic fibers levels, independently of extracellular levels of soluble tropoelastin, indicating that MAGP-2 stimulates elastic fiber assembly. This was associated with increased levels of matrix-associated MAGP-2. Electron microscopy showed that MAGP-2 specifically associates with microfibrils and that elastin globules primarily colocalize with MAGP-2-associated microfibrils, suggesting that microfibril-associated MAGP-2 facilitates elastic fiber assembly. MAGP-2 overexpression did not change levels of matrix-associated fibrillin-1, MAGP-1, fibulin-2, fibulin-5, or emilin-1, suggesting that microfibrils and other elastic fiber-associated proteins known to regulate elastogenesis do not mediate MAGP-2-induced elastic fiber assembly. Moreover, mutation analysis showed that MAGP-2 does not stimulate elastic fiber assembly through its RGD motif, suggesting that integrin receptor binding does not mediate MAGP-2-induced elastic fiber assembly. Because MAGP-2 interacts with Jagged-1 that controls cell-matrix interaction and cell motility, two key factors in elastic fiber macroassembly, microfibril-associated MAGP-2 may stimulate elastic fiber macroassembly by targeting the release of elastin globules from the cell membrane onto developing elastic fibers.

Early Emphysema in the Tight Skin and Pallid Mice

The nature of the development of emphysema in the tight skin (Tsk) and the pallid (Pa) mice are not well understood. We assessed the mechanical and nonlinear properties of the respiratory system, the alveolar structure, and the levels of microfibril-associated glycoproteins (MAGP) 1 and 2 in Tsk mice with developmental emphysema; in Pa mice, which are thought to develop adult onset emphysema; and their background, the C57BL/6 mice, at an age of 7 wk. Minor differences between collagen-related elastic properties of the lungs of the Pa and C57BL/6 mice were seen at this early age. The lungs of the Tsk mice were significantly softer yet more nonlinear than those of the Pa and C57BL/6 mice. The MAGP-1 levels were similar in all three groups. However, the level of MAGP-2, which is associated with both fibrillin-1 and collagen, was higher in the Tsk than in the Pa mice, which also had more MAGP-2 than the C57BL/6. Both the mean and the variance of alveolar diameters were larger in the Tsk than in the other two groups, while the variance in the Pa was larger than in the C57BL/6 mice, implying early development of heterogeneity. Using a network model of the parenchyma, we linked the pathophysiologic changes in the Tsk mice to mechanical forces and failure of the alveolar walls. Our findings suggest the possibility that MAGP-2-related abnormal collagen assembly, combined with mechanical forces, is involved in the progression of emphysema in the Tsk mice.

Dissecting Hypertension by Obesity Identifies a Locus at 1p36

The elevated arterial pressure that defines essential hypertension is regarded as the manifestation of a diverse array of interacting genetic and environmental causes. As such, hypertension is a heterogeneous disorder in which multiple contributing factors are responsible for the overarching phenotype of high blood pressure that is the primary clinical manifestation observed. Such heterogeneity has undoubtedly hampered efforts to elucidate the genetic basis of essential hypertension. Overweight and obesity are well known to increase the risk of essential hypertension. Yet, there are many hypertensive individuals whose weight is normal. So does obesity hypertension have a different underlying genetic cause than lean hypertension? In the current issue, Pausova et al report finding a locus with suggestive linkage to hypertension and then reanalyzed their data after dividing their families into lean and obese.1 Of considerable interest, the significance of the linkage peak increased for the obese families but disappeared in the case of the families with hypertension who were not obese. The striking contrast in results for each category of hypertension lends strong support to the idea that hypertension of obesity has a different genetic basis than other categories of hypertension. Not only is this finding important in discovery of the genetic basis of obesity hypertension, but it has obvious implications for approaches that might be used to identify the basis for other “intermediate phenotypes” of hypertension. The study by Pausova et al involved 55 extended families from the geographically remote French-Canadian Saguenay/Lac-St-Jean region of Quebec. This relatively small, isolated population has been spared the level of genetic “noise” present in populations elsewhere. As a result, the degree of genetic homogeneity should be elevated and likely contributed to the …

Aortic dissection: new frontiers in diagnosis and management: Part I: from etiology to diagnostic strategies.

Cardiovascular disease is the leading cause of death in most Western societies and is increasing steadily in many developing countries. Aortic diseases constitute an emerging share of the burden. New diagnostic imaging modalities, longer life expectancy in general, longer exposure to elevated blood pressure, and the proliferation of modern noninvasive imaging modalities have all contributed to the growing awareness of acute and chronic aortic syndromes. Despite recent progress in recognition of both the epidemiological problem and diagnostic and therapeutic advances, the cardiology community and the medical community in general are far from comfortable in understanding the spectrum of aortic syndromes and defining an optimal pathway to manage aortic diseases.1–13 This comprehensive review is organized in two parts, with a focus on the etiology, natural history, and classification (with vascular staging) of aortic wall disease in Part I and emphasis on therapeutic management and follow-up in Part II. Both parts may help to better integrate the complexities of acute aortic syndromes.

Distribution of the elastic fiber and associated proteins in flexor tendon reflects function.

The elastic fiber is known to be an important component of skin, lung, and vasculature. Much less is known about the distribution of elastin and elastic fiber-related proteins in connective tissues, yet genetic defects of elastic fiber constituents can lead to deficiencies in these tissues. For the first time, we determine the distribution of elastin, fibrillins 1 and 2, and microfibril-associated glycoproteins (MAGPs) 1 and 2 in the flexor digitorum profundus (FDP) tendon. Three functionally distinct regions of the FDP tendon, the fibrocartilagenous (FC) region, avascular/tensional (AV/T) region, and insertion region, were evaluated by immunohistochemical methods for these five proteins. Biochemical analysis of desmosine content, an elastin-specific cross-link, demonstrated the presence of elastin in each region, and this was verified histochemically. The fibrillins were found with elastin and also pericellularly with internal fibroblasts where elastin was not detected. Although there was overlapping distribution, fibrillin 2 was more prominent in the interior of the tendon while fibrillin 1 was prominent in outer cell layers that contained elastic fibers. Both MAGP-1 and -2 were found throughout the tendon, although the greatest abundance was near the tendon insertion to bone. Surprisingly, MAGP-1 demonstrated a filamentous appearance within the fibrocartilage that did not correspond to the fibrillin 1 or 2 or MAGP-2 staining pattern. Lastly, we have shown that a vincular membrane located along the dorsal surface of the tendon near the insertion has a very high elastin content and a unique interface with the tendon that consists of an elastic anchor within the tendon body.

Expression of 36-kDa microfibril-associated glycoprotein (MAGP-36) in human keratinocytes and its localization in skin

Microfibril-associated glycoprotein-36 (MAGP-36) is a recently isolated elastin-binding protein and considered to be a member of microfibril-associated glycoproteins (MAGPs). We studied the expression of MAGP-36 in cultured normal human keratinocytes and its localization in the skin. MAGP-36 was found to be expressed in cultured human keratinocytes by Western blot and RT-PCR assays. The levels of MAGP-36 (polypeptide and mRNA) and the number of MAGP-36-producing keratinocytes were greatly increased during Ca 2+-induced differentiation of keratinocytes. Immunohistochemical studies demonstrated that MAGP-36 colocalized with elastic fibers and formed candelabra like-fibers in the superficial dermis of normal skin. In the elderly skin of sun-exposed region, immunoreactivity of MAGP-36 in the superficial dermis disappeared. In the lesional skin of pseudoxanthoma elasticum which is an elastin-related disorder, immunoreactivity of MAGP-36 was found in the accumulation of disintegrated elastic fibers. The results show that MAGP-36 is a component of elastic fibers in the dermis and co-operates with elastin in normal and diseased conditions.

Molecular interactions of biglycan and decorin with elastic fiber components: biglycan forms a ternary complex with tropoelastin and microfibril-associated glycoprotein 1.

The interactions of the dermatan sulfate proteoglycans biglycan and decorin have been investigated with the elastic fiber components, tropoelastin, fibrillin-containing microfibrils, and microfibril-associated glycoproteins (MAGP) 1 and 2. Both proteoglycans were found to bind tropoelastin and fibrillin-containing microfibrils but not MAGPs 1 and 2 in solid phase binding assays. The specificity of the binding of biglycan and decorin to tropoelastin was confirmed by co-immunoprecipitation experiments and by the blocking of the interactions with elastin-derived peptides. Isolated core proteins from biglycan and decorin bound to tropoelastin more strongly than the intact proteoglycans, and there were no differences in the tropoelastin binding characteristics of distinct glucuronate-rich and iduronate-rich glycoforms of biglycan. These findings indicated that the binding sites were contained in the protein cores of the proteoglycans rather than the glycosaminoglycan side chains. Scatchard analysis showed that biglycan bound more avidly than decorin to tropoelastin with K(d) values estimated as 1.95 x 10(-7) m and 5.3 x 10(-7) m, respectively. In blocking experiments each proteoglycan showed extensive inhibition of binding of the other to tropoelastin but was most effective at blocking its own binding. This result suggested that biglycan and decorin had closely spaced but distinct binding sites on tropoelastin. Addition of the elastin-binding protein MAGP-1 to the assays enhanced the binding of biglycan to tropoelastin but had no effect on the decorin-tropoelastin interaction. Co-immunoprecipitation experiments showed that MAGP-1 interacted with biglycan but not decorin in the solution phase. The results indicated that biglycan specifically formed a ternary complex with tropoelastin and MAGP-1. Overall the study supports the concept that biglycan may have a specific role in the elastinogenic phase of elastic fiber formation.

Protein Interaction Studies of MAGP-1 with Tropoelastin and Fibrillin-1

Elastic fibers consist primarily of an amorphous elastin core associated with microfibrils, 10-12 nm in diameter, containing fibrillins and microfibril-associated glycoproteins (MAGPs). To investigate the interaction of MAGP-1 with tropoelastin and fibrillin-1, we expressed human MAGP-1 as a T7-tag fusion protein in Escherichia coli. Refolding of the purified protein produced a soluble form of MAGP-1 that displayed saturable binding to tropoelastin. Fragments of tropoelastin corresponding to the N-terminal, C-terminal, and central regions of the molecule were used to characterize the MAGP-1 binding site. Cleavage of tropoelastin with kallikrein, which cleaves after Arg(515) in the central region of the molecule, disrupted the interaction, suggesting that the separated N- and C-terminal fragments were insufficient to determine MAGP-1 binding to intact tropoelastin. In addition, no evidence of an interaction was observed between MAGP-1 and a tropoelastin construct consisting of domains 17-27 that brackets the kallikrein cleavage site, suggesting a complex mechanism of interaction between the two molecules. Binding of MAGP-1 was also tested with overlapping recombinant fibrillin-1 fragments. MAGP-1 bound to a region at the N terminus of fibrillin-1 in a calcium-dependent manner. In summary, these results suggest a model for the interaction of elastin with the microfibrillar scaffold.

Elastic fiber proteins in the glomerular mesangium in vivo and in cell culture

Glomerular capillaries of the mammalian kidney are exposed to high intraluminal hydrostatic pressures and require elastic constraint to maintain size, shape, and integrity. Previous morphological and functional studies indicated that the extracellular matrices of glomeruli, that is, basement membrane and mesangial matrix, contribute to glomerular resilience and mechanical stability. Immunofluorescence microscopy findings demonstrated elastic fiber components to be located in the renal vasculature, including glomeruli. The aim of this study was to clarify the exact glomerular localization, composition, and cellular production of these proteins. We examined the renal distribution of the elastic fiber proteins fibrillin-1, emilin, microfibril-associated glycoproteins (MAGPs) 1 and 2, latent transforming growth factor-binding protein-1 (LTBP-1), and elastin using immunohistology and immunoelectron microscopy of human, rat, and mouse kidneys. In mesangial cell cultures, we also studied the expression and extracellular deposition of such proteins by use of Northern blotting and immunocytochemistry. Fibrillin-1, emilin, MAGPs 1 and 2, and LTBP-1 were present in glomeruli of mouse, rat, and human kidney, where they were located predominantly in the mesangial extracellular matrix underlying glomerular endothelium and basement membrane. Several of these proteins, as well as elastin, were also expressed in the renal vasculature. While elastin localized to the glomerular vascular pole in afferent and efferent arterioles extending to Bowman's capsule, it was not found in the glomerular capillary tuft. Cultured mesangial cells of rat, mouse, and human kidneys expressed mRNAs of fibrillin-1, emilin, MAGP-2, and elastin, and the respective proteins localized within and outside of mesangial cells, as shown by immunocytochemistry. mRNA expression of fibrillin-1, emilin, and elastin was strong in quiescent mesangial cells; their gene expression was further up-regulated by transforming growth factor-beta1, while it was transiently reduced when cells were exposed to mitogenic 10% fetal calf serum and platelet-derived growth factor. These findings demonstrate that specific elastic fiber proteins are produced and secreted by mesangial cells. This process is regulated by growth factors. Their abundance in the extracellular matrix of the mesangium is in keeping with the concept that elastic fiber proteins contribute to the mechanical stability and elastic strength of the glomerular capillary tuft.

A Novel Hypothesis Regarding the Evolutionary Origins of the Immunoglobulin Fold

The recent cloning of two cDNAs (Clone 1 and Clone 5) that encode novel hypothetical proteins, combining an N-terminal Ig kappa-like domain with features that occur in microfibril-associated glycoproteins (MAGPs) and fibrinogen, raises the question of whether the Ig fold may have originated in association with functions that may be more primitive than soluble immunity. Pairwise alignments were performed to compare similarities of fibrinogen-beta, Clone 1 and an Ig kappa sequence. Clone 1 had two regions in its Ig domain with > 50% similarity to fibrinogen, while Ig kappa was virtually non-homologous to fibrinogen. This result suggests that Clone 1 is closer to their common ancestor. A neighbour-joining tree was computed, and it supported this interpretation. Three-dimensional modelling of the most highly conserved sequence revealed two antiparallel beta strands connected by a helix. These observations suggest that the ancestral gene for the immunoglobulin superfamily may have originated as a primitive sandwich-like fold, possibly used in matrix/cell communications.