Biomedical subjects

P H Vachon

Publications and source records attributed to P H Vachon.

At least 19 recordsLinked to original sources

PubMed2001

Differential sensitivity to apoptosis between the human small and large intestinal mucosae: linkage with segment-specific regulation of BCL-2 homologs and involvement of signaling pathways.

The small and large intestines differ in their expression profiles of Bcl-2 homologs. Intestinal segment-specific Bcl-2 homolog expression profiles are acquired as early as by mid-gestation (18-20 weeks) in man. In the present study, we examined the question whether such distinctions underlie segment-specific control mechanisms of intestinal cell survival. Using mid-gestation human jejunum and colon organotypic cultures, we analyzed the impact of growth factors (namely insulin; 10 microg/ml) and pharmacological compounds that inhibit signal transduction molecules/pathways (namely tyrosine kinases, Fak, P13-K/Akt, and MEK/Erk) on cell survival and Bcl-2 homolog expression (anti-apoptotic: Bcl-2, Bcl-X(L), Mcl-1; pro-apoptotic: Bax, Bak, Bad). The relative activation levels of p125Fak, p42Erk-2, and p57Akt were analyzed as well. Herein, we report that (1) the inhibition of signal transduction molecules/pathways revealed striking differences in their impact on cell survival in the jejunum and colon (e.g., the inhibition of p125Fak induced apoptosis with a significantly greater extent in the jejunum [approximately 43%] than in the colon [approximately 24%]); (2) sharp distinctions between the two segments were noted in the modulatory effects of the various treatments on Bcl-2 homolog steady-state levels (e.g., inhibition of tyrosine kinase activities in the jejunum down-regulated all anti-apoptotics analyzed while increasing Bax, whereas the same treatment in the colon down-regulated Bcl-X(L) only and increased all pro-apoptotics); and (3) in addition to their differential impact on cell survival and Bcl-2 homolog expression, the MEK/Erk and P13-K/Akt pathways were found to be distinctively regulated in the jejunum and colon mucosae (e.g., insulin in the jejunum increased p42Erk-2 activation without affecting that of p57Akt, whereas the same treatment in the colon decreased p42Erk-2 activation while increasing that of p57Akt). Altogether, these data show that intestinal cell survival is characterized by segment-specific susceptibilities to apoptosis, which are in turn linked with segmental distinctions in the involvement of signaling pathways and the regulation of Bcl-2 homolog steady-state levels. Therefore, these indicate that cell survival is subject to segment-specific control mechanisms along the proximal-distal axis of the intestine.

Apoptosis↗

PubMed2001

Human intestinal epithelial cell survival: differentiation state-specific control mechanisms.

To investigate whether human intestinal epithelial cell survival involves distinct control mechanisms depending on the state of differentiation, we analyzed the in vitro effects of insulin, pharmacological inhibitors of Fak, MEK/Erk, and PI3-K/Akt, and integrin (beta1, beta4)-blocking antibodies on the survival of the well-established human Caco-2 enterocyte-like and HIEC-6 cryptlike cell models. In addition, relative expression levels of six Bcl-2 homologs (Bcl-2, Bcl-X(L), Mcl-1, Bax, Bak, and Bad) and activation levels of Fak, Erk-2, and Akt were analyzed. Herein, we report that 1) the enterocytic differentiation process results in the establishment of distinct profiles of Bcl-2 homolog expression levels, as well as p125(Fak), p42(Erk-2), and p57(Akt) activated levels; 2) the inhibition of Fak, of the MEK/Erk pathway, or of PI3-K, have distinct impacts on enterocytic cell survival in undifferentiated (subconfluent Caco-2, confluent HIEC-6) and differentiated (30 days postconfluent Caco-2) cells; 3) exposure to insulin and the inhibition of Fak, MEK, and PI3-K resulted in differentiation state-distinct modulations in the expression of each Bcl-2 homolog analyzed; and 4) Fak, beta1 and beta4 integrins, as well as the MEK/Erk and PI3-K/Akt pathways, are distinctively involved in cell survival depending on the state of cell differentiation. Taken together, these data indicate that human intestinal epithelial cell survival is regulated according to differentiation state-specific control mechanisms.

Anoikis↗

PubMed2001

Early acquisition of bowel segment-specific Bcl-2 homolog expression profiles during development of the human ileum and colon.

The adult small and large intestines display distinct expression profiles of Bcl-2 homologs, known regulators of apoptosis. This is thought to indicate that control mechanisms of intestinal apoptosis are gut segment-specific. Little is known on the expression of Bcl-2 homologs during gut development. In man, intestinal features and functions are acquired largely by mid-gestation (18-20 wks); the question whether segment-specific controls of intestinal apoptosis are also acquired early during development remains open. In the present study, we approached this by investigating the expression of six Bcl-2 homologs (Bcl-2, Bcl-XL, Mcl-1, Bax, Bak, Bad), and one nonhomologous associated molecule (Bag-1), during development of the human ileum and colon (12-20 wks of gestation). Beginning at 18 wks, we found that the epithelial localization of Bcl-2 homologs displayed differential patterns (or gradients) in both the ileum and colon; however, the patterns of some of the homologs differed between the two segments. For instance, Bag-1 and Bcl-2 exhibited crypt-villus decreasing gradients of expression in the ileum but not in the colon, whereas Mcl-1 displayed differing compartimentalizations between the two segments. Further analyses indicated that the steady-state expression levels of Bcl-2 homologs underwent modulations between 12 and 20 wks; however, the observed developmental profiles contrasted significantly between the two segments. For example, Bcl-2, Bag-1 and Bak levels increased in the colon, but the levels of these same homologs decreased in the ileum. Furthermore, by 18-20 wks, we found that the expression levels of each Bcl-2 homolog analyzed differed greatly between the ileum and colon. Altogether, these data indicate that the expression of Bcl-2 homologs is modulated differentially during human gut development in order to establish, by mid-gestation, distinct expression profiles for the small and large intestines. This in turn suggests that gut segment-specific control mechanisms of human intestinal apoptosis are acquired early during fetal life.

Apoptosis↗

PubMed2000

MEK/ERK signaling pathway regulates the expression of Bcl-2, Bcl-X(L), and Mcl-1 and promotes survival of human pancreatic cancer cells.

BACKGROUND AND AIMS: Growth factors are well known for their participation in the regulation of cell proliferation and survival. However, the intracellular signaling pathways by which growth factors promote survival are still poorly understood. In the present study, using the MIA PaCa-2 cell line, a well-established model of pancreatic cancer cells, we analyzed the roles of ERK1/2 activities in the regulation of cell survival and investigated some of the mechanisms involved. METHODS: The ability of the MEK inhibitor PD98059 to modulate survival of the MIA PaCa-2 cells was evaluated, and the responses were correlated with expression of Bcl-2 homologs and caspases 1, 3, 6, 8, and 9 activities. RESULTS: Herein, we showed that inhibition of ERK1/2 activities caused (1) a G1 arrest; (2) a down-regulation of the expression levels of the anti-apoptotic homologs Bcl-2, Mcl-1, and Bcl-X(L) without affecting the pro-apoptotic levels of Bax and Bak; (3) a promotion of caspases 3, 6, 8, and 9 activities; (4) a stimulation of PARP cleavage; and (5) a programmed cell death by apoptosis. CONCLUSION: Our data suggest that activation of the ERK pathway functions to protect pancreatic tumor cells from apoptosis as well as to regulate their progression in the cell cycle.

Apoptosis↗

PubMed2000

Early establishment of epithelial apoptosis in the developing human small intestine.

In the adult small intestine, the dynamic renewal of the epithelium is characterized by a sequence of cell production in the crypts, cell maturation and cell migration to the tip of villi, where apoptosis is undertaken. Little is known about enterocytic apoptosis during development. In man, intestinal architectural features and functions are acquired largely by mid-gestation (18-20 wks); the question whether the establishment of enterocytic apoptotic processes parallels or not the acquisition of other intestinal functional features remains open. In the present study, we approached this question by examining enterocytic apoptosis during development of the human jejunum (9-20 wks gestation), using the ISEL (in situ terminal uridine deoxynucleotidyl nick-end labelling) method. Between 9 and 17 wks, apoptotic enterocytes were not evidenced. However, beginning at the 18 wks stage, ISEL-positive enterocytes were regularly observed at the tip of villi. Since the Bcl-2 family of proteins constitutes a critical checkpoint in apoptosis, acting upstream of the apoptotic machinery, we investigated the expression of six Bcl-2 homologs (Bcl-2, Bcl-X(L), Mcl-1, Bax, Bak, Bad) and one non-homologous associated molecule (Bag-1). By immunofluorescence, we found that all homologs analyzed were expressed by enterocytes between 9 and 20 wks. However, Bcl-2 homologs underwent a gradual compartmentalization of epithelial expression along the maturing crypt-villus axis, to establish gradients of expression by 18-20 wks. Western blot analyses indicated that the expression levels of Bcl-2 homologs were modulated during morphogenesis of the crypt-villus axis, in parallel to their gradual compartmentalization of expression. Altogether, these data suggest that regulatory mechanisms of human enterocytic apoptosis become established by mid-gestation (18-20 wks) and coincide with the maturation of the crypt-villus axis of cell proliferation, differentiation and renewal.

Apoptosis↗

PubMed1998

Merosin-deficient congenital muscular dystrophy. Partial genetic correction in two mouse models.

Humans and mice with deficiency of the alpha2 subunit of the basement membrane protein laminin-2/merosin suffer from merosin-deficient congenital muscular dystrophy (MCMD). We have expressed a human laminin alpha2 chain transgene under the regulation of a muscle-specific creatine kinase promoter in mice with complete or partial deficiency of merosin. The transgene restores the synthesis and localization of merosin in skeletal muscle, and greatly improves muscle morphology and integrity and the health and longevity of the mice. However, the transgenic mice share with the nontransgenic dystrophic mice a progressive lameness of hind legs, suggestive of a nerve defect. These results indicate that the absence of merosin in tissues other than the muscle, such as nervous tissue, is a critical component of MCMD. Future gene therapies of human MCMD, and perhaps of other forms of muscular dystrophy, may require restoration of the defective gene product in multiple tissues.

Animals↗

PubMed1998

Disruption of the lama2 gene in embryonic stem cells: laminin alpha 2 is necessary for sustenance of mature muscle cells.

Mutations in the gene coding for the alpha 2 chain of laminin-2 and -4 (merosin) cause a severe form of congenital muscular dystrophy in humans and mice. To establish a defined model for in vitro and in vivo studies of the role of laminin alpha 2/merosin in development and cell and tissue function, we generated several lines of mutant embryonic stem (ES) cell with disruption of the laminin alpha 2 chain gene. We find that homozygous mutant ES cells differentiate normally in vitro, giving rise to cardiomyocytes, myotubes, and smooth muscle cells in addition to many other cell types. However, the myotubes that are formed are unstable. They detach, collapse, and degenerate, a process which is initiated at the appearance of the mature, contractile phenotype of the cells. We propose that the detachment and death of contracting myotubes in vitro has its counterpart in vivo and that contraction-induced myofiber damage, along with the lack of survival cues provided by laminin alpha 2/merosin, is a significant contribution to muscle degeneration in merosin-deficient muscular dystrophy.

Animals↗

PubMed1998

Identification, distribution, and tissular origin of the alpha5(IV) and alpha6(IV) collagen chains in the developing human intestine.

The basement membrane type IV collagen is a family composed of six genetically distinct but structurally similar polypeptide chains, alpha1-alpha6. The alpha1(IV) and alpha2(IV) chains are ubiquitous components of all BMs whereas the other four have a restricted tissue distribution. In the present study, we have analyzed the expression, distribution, and cellular origin of the alpha5(IV) and alpha6(IV) chains in the developing and adult human small intestine and in well-characterized in vitro models by indirect immunofluorescence, Western blot, and RT-PCR. We have found that in the fetal small intestine, alpha(IV) and alpha6(IV) are present in the epithelial BM and, in contrast to alpha1(IV) and alpha2(IV), are produced by both epithelial and mesenchymal cells. A distinct tissular origin for the alpha1/alpha2(IV) and alpha5/alpha6(IV) chains suggests that alpha5(IV) and alpha6(IV) associate as a heterotrimer in this organ. We have also found that a particular situation of alpha5(IV)/alpha6(IV) chain expression occurs in the adult intestine. Indeed, as compared with the fetal intestine, alpha6(IV) chain production is maintained while the expression of the alpha5(IV) chain is substantially reduced. Altered expression of the alpha5(IV) chain was also observed in the differentiating enterocytic-like Caco-2/15 cells, suggesting that in the intestinal model, the alpha5(IV) chain is subject to a regulated expression. Taken together, these observations indicate that the human intestinal epithelial BM contains up to four type IV collagen chains: the classical alpha1(IV)/alpha2(IV) chains, which originate from mesenchymal cells, and the alpha5(IV)/alpha6(IV) chains, which are of both epithelial and mesenchymal origin and have their expression regulated throughout development.

Caco-2 Cells↗

PubMed1997

Integrins (alpha7beta1) in muscle function and survival. Disrupted expression in merosin-deficient congenital muscular dystrophy.

Mutations in genes coding for dystrophin, for alpha, beta, gamma, and delta-sarcoglycans, or for the alpha2 chain of the basement membrane component merosin (laminin-2/4) cause various forms of muscular dystrophy. Analyses of integrins showed an abnormal expression and localization of alpha7beta1 isoforms in myofibers of merosin-deficient human patients and mice, but not in dystrophin-deficient or sarcoglycan-deficient humans and animals. It was shown previously that skeletal muscle fibers require merosin for survival and function (Vachon, P.H., F. Loechel, H. Xu, U.M. Wewer, and E. Engvall. 1996. J. Cell Biol. 134:1483-1497). Correction of merosin deficiency in vitro through cell transfection with the merosin alpha2 chain restored the normal localization of alpha7beta1D integrins as well as myotube survival. Overexpression of the apoptosis-suppressing molecule Bcl-2 also promoted the survival of merosin-deficient myotubes, but did not restore a normal expression of alpha7beta1D integrins. Blocking of beta1 integrins in normal myotubes induced apoptosis and severely reduced their survival. These findings (a) identify alpha7beta1D integrins as the de facto receptors for merosin in skeletal muscle; (b) indicate a merosin dependence for the accurate expression and membrane localization of alpha7beta1D integrins in myofibers; (c) provide a molecular basis for the critical role of merosin in myofiber survival; and (d) add new insights to the pathogenesis of neuromuscular disorders.

Animals↗

PubMed1997

Mouse adhalin: primary structure and expression during late stages of muscle differentiation in vitro.

Adhalin, or alpha-sarcoglycan, is a 50-kDa glycoprotein that was originally characterized as a muscle membrane protein. The importance of adhalin is suggested by the diseases associated with its absence, notably the limb-girdle muscular dystrophies. However, the function of adhalin is unknown. To analyze the biological roles of adhalin, we cloned the mouse adhalin cDNA, raised peptide-specific antibodies to its cytoplasmic domain, and examined its expression and localization in vivo and in vitro. The mouse adhalin sequence was 80% identical to that of human, rabbit, and hamster. Adhalin was specifically expressed in striated muscle cells and their immediate precursors, and absent in many other cell types. Adhalin expression in embryonic mouse muscle was coincident with primary myogenesis. Its expression was found to be up-regulated at mRNA and protein levels during myogenic differentiation in vitro. The proper localization of adhalin to the muscle cell membrane was observed only in late stages of myotube maturation, coincident with the re-distribution of caveolin-3 and dystrophin. These data suggest that adhalin is highly specific for striated muscle and that it is linked with the formation of a fully functional muscle fiber.

Amino Acid Sequence↗

PubMed1997

Relation between integrin alpha7Bbeta1 expression in human intestinal cells and enterocytic differentiation.

BACKGROUND & AIMS: Cell-laminin interactions are principally mediated by specific membrane receptors of the integrin family. The integrin alpha7beta1 is one of them. Its expression in the intestine has not yet been investigated although it appears to be a key element in muscle cell differentiation. In this study, the expression of its three known isoforms has been analyzed in developing and adult small intestine and in intestinal cell lines. METHODS: The expression of the integrin alpha7beta1 was analyzed by indirect immunofluorescence, Western blotting, immunoprecipitation, and reverse-transcription polymerase chain reaction. RESULTS: The alpha7B isoform, but not the alpha7A and C isoforms, was detected in intestinal epithelial cells. In vivo, the presence of the alpha7B subunit was closely paralleled with (1) acquisition of differentiation characteristics during development and along the crypt-villus axis in the adult small intestine and (2) loss of enterocytic functions in the re-differentiated colonic epithelium. In vitro, the expression of alpha7B was also shown to correlate with the acquisition of enterocytic functions. In Caco-2 cells, the alpha7Bbeta1 integrin was found transiently up-regulated at the onset of sucrase-isomaltase expression. CONCLUSIONS: Taken together, these results suggest that alpha7Bbeta1 expression is correlated with human intestinal cell differentiation.

Amino Acid Sequence↗

PubMed1996

Uncoordinated, transient mosaic patterns of intestinal hydrolase expression in differentiating human enterocytes.

The heterogenous expression of brush border membrane hydrolases by the human enterocyte-like Caco-2 cell line during morphological and functional differentiation in vitro was investigated at the cellular level. Indirect immunofluorescence revealed that the heterogeneous ("mosaic") expression of sucrase-isomaltase, lactase, aminopeptidase N, and alkaline phosphatase was, in fact, transient in nature. The labeling indexes for each hydrolase gradually increased during culture at postconfluence in order to reach a maximum (> or = 90%) after 30 days, concomitant with an upregulation of their respective protein expression levels. In contrast, dipeptidylpeptidase IV labeling remained relatively constant. Backscattered electron imaging analysis in midstage (12 days postconfluence) monolayers demonstrated a lack of correlation between brush border membrane development and expression of each enzyme studied. Moreover, double immunostaining revealed that none of the other four hydrolases correlated directly with sucrase-isomaltase expression. Finally, immunodetection for the proliferation-associated antigen KI-67 revealed a transient mosaic pattern of proliferation which was inversely related to Caco-2 cell differentiation. These data indicate that enterocytic differentiation-related (as well as proliferation-related) gene expression in Caco-2 cells is regulated but uncoordinated at the cellular level, suggesting that an overall control mechanism is lacking.

Alkaline Phosphatase↗

PubMed1996

Merosin and laminin in myogenesis; specific requirement for merosin in myotube stability and survival.

Laminin (laminin-1; alpha 1-beta 1-gamma 1) is known to promote myoblast proliferation, fusion, and myotube formation. Merosin (laminin-2 and -4; alpha 2-beta 1/beta 2-gamma 1) is the predominant laminin variant in skeletal muscle basement membranes; genetic defects affecting its structure or expression are the causes of some types of congenital muscular dystrophy. However, the precise nature of the functions of merosin in muscle remain unknown. We have developed an in vitro system that exploits human RD and mouse C2C12 myoblastic cell lines and their clonal variants to study the roles of merosin and laminin in myogenesis. In the parental cells, which fuse efficiently to multinucleated myotubes, merosin expression is upregulated as a function of differentiation while laminin expression is downregulated. Cells from fusion-deficient clones do not express either protein, but laminin or merosin added to the culture medium induced their fusion. Clonal variants which fuse, but form unstable myotubes, express laminin but not merosin. Exogenous merosin converted these myotubes to a stable phenotype, while laminin had no effect. Myotube instability was corrected most efficiently by transfection of the merosin-deficient cells with the merosin alpha 2 chain cDNA. Finally, merosin appears to promote myotube stability by preventing apoptosis. Hence, these studies identify novel biological functions for merosin in myoblast fusion and muscle cell survival; furthermore, these explain some of the pathogenic events observed in congenital muscular dystrophy caused by merosin deficiency and provide in vitro models to further investigate the molecular mechanisms of this disease.

Animals↗

PubMed1995

Appearance and distribution of laminin A chain isoforms and integrin alpha 2, alpha 3, alpha 6, beta 1, and beta 4 subunits in the developing human small intestinal mucosa.

BACKGROUND: Laminin, a major component of basement membranes, is well known in its classical heterotrimeric form (B1-A-B2) to regulate diverse biological functions, including cell polarization and differentiation. However, the role of merosin, a laminin-like molecule in which an M chain is substituted for its homologous A chain, remains largely unknown. METHODS: In the present study, we analyzed by indirect immunofluorescence the expression and distribution of these four laminin chains as well as the integrins alpha 2 beta 1, alpha 3 beta 1, alpha 6 beta 1, and alpha 6 beta 4, four potential receptors, at the epithelial-mesenchymal interface of the developing human small intestine, with a panel of specific monoclonal antibodies. RESULTS: Beginning at 7 weeks of gestation and throughout mucosal organogenesis, the B1 and B2 chains were uniformly detected at the epithelial basement membrane. The A chain also was detected beginning at 7 weeks, and its distribution at the basement membrane remained uniform throughout villus (9+ weeks) and crypt (16+ weeks) formation. In contrast, M chain expression was not observed until 16 weeks; between 16 and 20 weeks, it was exclusively associated with the base of epithelial cells that comprised the forming crypts. Integrins alpha 6 beta 1 and alpha 6 beta 4, as determined by their subunit immunolocalization, appeared to be expressed by all enterocytes from 7 to 20 weeks. In contrast, the expression of the alpha 2 beta 1 and alpha 3 beta 1 integrins was found time- and site-restricted. The alpha 2 subunit was predominantly detected in the epithelial cells of the intervillous area and its derivative, the crypt, whereas the alpha 3 subunit was strongly expressed by all epithelial cells except those located at the bottom of 19-20-week-old crypts. CONCLUSIONS: Taken together, these observations demonstrate that both compositional changes in the basement membrane and differential expression of receptors occur during human intestinal organogenesis, suggesting that epithelial cell-matrix interactions play a role during development.

Antigens, CD↗

PubMed1995

Cellular fibronectin expression is down-regulated at the mRNA level in differentiating human intestinal epithelial cells.

The expression of human cellular fibronectin (HFN) was analyzed in relation to the differentiation process of the human enterocyte-like cell line Caco-2. A single approximately 290-kDa form of HFN, corresponding to a 10.0-kb mRNA species, was observed in Caco-2 cells. The expression levels of both protein and mRNA were found to decrease to undetectable levels concomitantly to the differentiation process of these cells. This decline in HFN expression was correlated with the expression of sucrase-isomaltase (a specific marker of intestinal cell differentiation). These results indicate that intestinal epithelial expression of HFN is down-regulated through its mRNA levels and is correlated with the acquisition of the differentiated enterocytic phenotype.

Biomarkers↗

PubMed1995

Extracellular heterotrimeric laminin promotes differentiation in human enterocytes.

To investigate the role of laminin (Ln) and merosin (a Ln variant) in the modulation of intestinal epithelial cell differentiation, we have analyzed their functional expression as well as their potential influence during the differentiation process of Caco-2 cells, a human cell line unique in its property to differentiate into a mature enterocyte-like cell type in vitro. By indirect immunofluorescence and Western blotting, Caco-2 cells have been found to express the B1 and B2 chains of Ln, as well as a heavy approximately 350- to 370-kDa chain related to the human A chain, but not the M chain, of merosin. A gradual deposition of this A-like chain-containing Ln molecule has been observed as Caco-2 cells undergo differentiation. At the cellular level, a clear relationship between basal staining for the A chain and apical staining for the brush-border membrane enzyme sucrase-isomaltase (SI) has been observed. Human Ln, used as substratum, has been found to increase significantly the expression of SI and lactase in Caco-2 cells, whereas both Ln and human merosin have been shown to stimulate aminopeptidase N and alkaline phosphatase expression. Taken together, these data indicate that enterocytic differentiation-related gene expression is promoted by an extracellular deposition of Ln and may be susceptible to a differential modulation by variant forms of the molecule.

Cell Differentiation↗

PubMed1994

Expression of the alpha-5(IV) collagen chain in the fetal human small intestine.

BACKGROUND/AIMS: The basement membrane type IV collagen is a family composed of at least five genetically distinct but structurally similar polypeptide chains, alpha 1-alpha 5. The alpha 1(IV) and alpha 2(IV) chains are ubiquitous components of basement membranes, whereas the alpha 3(IV), alpha 4(IV), and alpha 5(IV) chains have a restricted tissue distribution. The aim of this study was to analyze the presence of these minor type IV collagen chains in the small intestinal mucosa. METHODS: The expression of type IV collagen chains in the developing and adult human small intestine was determined by indirect immunofluorescence with monoclonal and polyclonal antibodies. Western blotting and Northern hybridization analysis were also used to additionally investigate the expression of the alpha 1(IV) and alpha 5(IV) chains. RESULTS: The alpha 3-alpha 5(IV) chains were absent from the adult epithelium, but, surprisingly, the alpha 5(IV) chain was consistently detected in the fetal mucosa. Its expression was confirmed by Western blotting, complementary DNA polymerase chain-reaction amplification, and Northern hybridization analysis. CONCLUSIONS: The alpha 5(IV) chain of collagen is expressed in the fetal but not adult human intestinal epithelium. Its position at the basolateral domain of epithelial cells suggests a potential role for this molecule during development.

Aging↗

PubMed1994

Reciprocal expression of laminin A-chain isoforms along the crypt-villus axis in the human small intestine.

BACKGROUND/AIMS: Intestinal epithelial cell proliferation, migration, and differentiation are susceptible to various influences along the crypt-villus axis including compositional changes in the basement membrane and differential expression of receptors for these components. However, laminin has been consistently detected at the epithelial basement membrane without significant variation in relation to the crypt-villus functional unit. The aim of this study was to examine the distribution of individual laminin chains. METHODS: The patterns of distribution of laminin A, M (an A-chain variant), B1, and B2 chains as well as the integrins alpha 6 beta 1 and alpha 6 beta 4, two laminin receptors, were determined by indirect immunofluorescence in the adult human small intestine. RESULTS: Markedly distinct patterns of laminin chain expression were observed along the crypt-villus axis. The A chain was found predominantly associated with the differentiated epithelial cells on the villus whereas the M chain was restricted to the basement membrane of crypts. However, both B1 and B2 chains were detected all along the intestinal basement membrane. Furthermore, alpha 6 beta 1 and alpha 6 beta 4 integrins were found to be expressed by all enterocytes. CONCLUSIONS: These observations show a reciprocal expression of laminin isoforms along the crypt-villus axis and support the concept that the intestinal epithelial basement membrane is subjected to intricate compositional changes.

Adult↗