J. Najib - Academia.edu (original) (raw)

Papers by J. Najib

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2014

The Journal of endocrinology, 1999

Peroxisome proliferator-activated receptor gamma (PPARgamma), a fatty acid-activated nuclear rece... more Peroxisome proliferator-activated receptor gamma (PPARgamma), a fatty acid-activated nuclear receptor, is implicated in adipocyte differentiation and insulin sensitisation. In view of the association of dietary fat intake and bowel disease, the expression of PPARgamma in rodent and human intestine was studied. Expression of PPARgamma mRNA was examined by Northern blot hybridisation, RNase protection, and/or competitive RT-PCR assays, whereas PPARgamma protein levels were evaluated by immunoblotting and immunohistochemistry. PPARgamma mRNA and protein were abundantly expressed in colon relative to the small intestine both in rodents and in man. Interestingly, expression of PPARgamma was primarily localised in the more differentiated epithelial cells in the colon. The level of expression of PPARgamma in colon was similar to the levels seen in adipose tissue. Expression of PPARgamma increased from proximal to distal segments of the colon in man. In Caco-2 and HT-29 human adenocarcinoma...

Nature medicine, 1998

The development of colorectal cancer, one of the most frequent cancers, is influenced by prostagl... more The development of colorectal cancer, one of the most frequent cancers, is influenced by prostaglandins and fatty acids. Decreased prostaglandin production, seen in mice with mutations in the cyclooxygenase 2 gene or in animals and humans treated with cyclooxygenase inhibitors, prevents or attenuates colon cancer development. There is also a strong correlation between the intake of fatty acids from animal origin and colon cancer. Therefore, the peroxisome proliferator-activated receptor gamma (PPARgamma), a downstream transcriptional mediator for prostaglandins and fatty acids which is highly expressed in the colon may be involved in this process. Activation of PPARgamma by two different synthetic agonists increased the frequency and size of colon tumors in C57BL/6J-APCMin/+ mice, an animal model susceptible to intestinal neoplasia. Tumor frequency was only increased in the colon, and did not change in the small intestine, coinciding with the colon-restricted expression of PPARgamma...

European Journal of Biochemistry, 1999

In rodents, cholesterol for adrenal steroidogenesis is derived mainly from high-density lipoprote... more In rodents, cholesterol for adrenal steroidogenesis is derived mainly from high-density lipoproteins (HDL) via the HDL receptor, scavenger receptor-BI (SR-BI). In humans cholesterol for steroidogenesis is considered to be derived from the low-density lipoprotein (LDL) receptor pathway, and the contribution of SR-BI to that is unknown. In the present study SR-BI expression and regulation by steroidogenic stimuli was analysed in human adrenocortical cells and compared with LDL receptor expression. In addition, the functional contribution of both receptors for cholesteryl ester delivery to human adrenocortical cells was compared. Northern blot and reverse transcription-PCR amplification and sequence analysis demonstrated the presence of SR-BI mRNA in foetal and adult human adrenal cortex. Furthermore, SR-BI mRNA was expressed to similar levels in human primary adrenocortical and adrenocortical carcinoma NCI-H295 cells, indicating its presence in the steroid-producing cells. Treatment of NCI-H295 cells with 8Br-cAMP, a stimulator of glucocorticoid synthesis via the protein kinase A second messenger signal transduction pathway, resulted in an increase of both SR-BI and LDL receptor mRNA levels in a time- and dose-dependent manner. The induction of SR-BI and LDL receptor by cAMP was independent of ongoing protein synthesis and occurred at the transcriptional level. Ligand blot experiments indicated that a protein of similar size to SR-BI is the major HDL-binding protein in NCI-H295 cells. Western blot analysis demonstrated that cAMP treatment increased the levels of LDL receptor and, to a lesser extent, SR-BI protein in NCI-H295 cells. Binding and uptake of cholesterol was quantitatively smaller from HDL than from LDL, both in basal as well as in cAMP-stimulated cells. Scatchard analysis under basal conditions indicated that NCI-H295 cells express twice as many specific binding sites for LDL than for HDL. Dissociation constant values (Kd; in nm) were approximately five times higher for HDL than for LDL, indicating a lower affinity of HDL compared with LDL. The combined effects of these two parameters and the low cholesteryl ester content of HDL subfraction 3 (HDL3) contributes to a lower cholesteryl ester uptake from HDL than from LDL by the NCI-H295 cells. In conclusion, both the SR-BI and LDL receptor genes are expressed in the human adrenal cortex and coordinately regulated by activators of glucocorticoid synthesis. In contrast to rodents, in human adrenocortical cells the HDL pathway of cholesterol delivery appears to be of lesser importance than the LDL pathway. Nevertheless, the SR-BI pathway may become of major importance in conditions of functional defects in the LDL receptor pathway.

Proceedings of the National Academy of Sciences, 1998

Journal of Biological Chemistry, 1998

Peroxisome proliferator-activated receptors (PPARs) have been implicated in metabolic diseases, s... more Peroxisome proliferator-activated receptors (PPARs) have been implicated in metabolic diseases, such as obesity, diabetes, and atherosclerosis, due to their activity in liver and adipose tissue on genes involved in lipid and glucose homeostasis. Here, we show that the PPARalpha and PPARgamma forms are expressed in differentiated human monocyte-derived macrophages, which participate in inflammation control and atherosclerotic plaque formation. Whereas PPARalpha is already present in undifferentiated monocytes, PPARgamma expression is induced upon differentiation into macrophages. Immunocytochemistry analysis demonstrates that PPARalpha resides constitutively in the cytoplasm, whereas PPARgamma is predominantly nuclear localized. Transient transfection experiments indicate that PPARalpha and PPARgamma are transcriptionally active after ligand stimulation. Ligand activation of PPARgamma, but not of PPARalpha, results in apoptosis induction of unactivated differentiated macrophages as measured by the TUNEL assay and the appearance of the active proteolytic subunits of the cell death protease caspase-3. However, both PPARalpha and PPARgamma ligands induce apoptosis of macrophages activated with tumor necrosis factor alpha/interferon gamma. Finally, PPARgamma inhibits the transcriptional activity of the NFkappaB p65/RelA subunit, suggesting that PPAR activators induce macrophage apoptosis by negatively interfering with the anti-apoptotic NFkappaB signaling pathway. These data demonstrate a novel function of PPAR in human macrophages with likely consequences in inflammation and atherosclerosis.

Journal of Biological Chemistry, 1997

Apolipoprotein (apo) E, a constituent of several lipoproteins, is a ligand for the low density li... more Apolipoprotein (apo) E, a constituent of several lipoproteins, is a ligand for the low density lipoprotein receptor, and this interaction is important for maintaining cholesterol and triglyceride homeostasis. We have used a gene replacement strategy to generate mice that express the human apoE3 isoform in place of the mouse protein. The levels of apoE mRNA in various tissues are virtually the same in the human apoE3 homozygous (3/3) mice and their littermates having the wild type mouse allele (؉/؉). Total cholesterol and triglyceride levels in fasted plasma from the 3/3 mice were not different from those in the ؉/؉ mice, when maintained on a normal (low fat) chow diet. We found, however, notable differences in the distribution of plasma lipoproteins and apolipoprotein E between the two groups: ␤-migrating lipoproteins and plasma apoB100 levels are decreased in the 3/3 mice, and the apoE distribution is shifted from high density lipoproteins to larger lipoprotein particles. In addition, the fractional catabolic rate of exogenously administered remnant particles without apoE was 6-fold slower in the 3/3 mice compared with the ؉/؉ mice. When the 3/3 and ؉/؉ animals were fed a high fat/high cholesterol diet, the 3/3 animals responded with a dramatic increase (5-fold) in total cholesterol compared with the ؉/؉ mice (1.5-fold), and after 12 weeks on this same diet the 3/3 animals developed significantly (at least 13-fold) larger atherosclerotic plaques in the aortic sinus area than the ؉/؉ animals. Thus the structural differences between human APOE3 and mouse ApoE proteins are sufficient to cause an increased susceptibility to dietary-induced hypercholesterolemia and atherosclerosis in the 3/3 mice.

Journal of Biological Chemistry, 1997

ApoC-III overexpression in mice results in severe hypertriglyceridemia due primarily to a delay i... more ApoC-III overexpression in mice results in severe hypertriglyceridemia due primarily to a delay in the clearance of triglyceride-rich lipoproteins. We have, in primary cultures of rat hepatocytes, characterized a lipolysis-stimulated receptor (LSR). The apparent number of LSR that are available on rat liver plasma membranes is negatively correlated with plasma triglyceride concentrations measured in the fed state. We therefore proposed that the primary physiological role of the LSR is to contribute to the cellular uptake of triglyceriderich lipoproteins. We have now tested the effect of apoC-III on the binding of triglyceride-rich lipoproteins to LSR. Supplementation of 125 I-very low density lipoprotein (VLDL) with apoC-III inhibited the LSR-mediated binding, internalization, and degradation of 125 I-VLDL in primary cultures of rat hepatocytes. Studies using isolated rat liver plasma membranes showed that enrichment of human VLDL and chylomicrons with synthetic or purified human apoC-III decreased their binding to the LSR by about 40%. Supplementation of triglyceride-rich lipoproteins under the same conditions with human apoC-II had no such inhibitory effect, despite the fact that this apoprotein bound as efficiently as apoC-III to these particles.

Genomics, 2000

Uptake of fatty acids into cells is a controlled process in part regulated by fatty acid transpor... more Uptake of fatty acids into cells is a controlled process in part regulated by fatty acid transport proteins (FATPs), which facilitate the transport of fatty acids across the cell membrane. In this study the structure of the human FATP-1 (HGMW-approved symbol SLC27A1) cDNA and gene was determined, and the expression of its mRNA in human was characterized. Muscle and adipose tissue have the highest levels of FATP-1 mRNA, small intestine has intermediate levels, and FATP-1 mRNA is barely detectable in liver. The human FATP-1 gene has 12 exons and extends over more than 13 kb of genomic DNA. The FATP gene maps to chromosome 19p13.1 by fluorescence in situ hybridization, a region previously suggested to be implicated in the determination of small dense low-density lipoprotein (LDL). Knowledge of the gene structure and chromosomal localization will allow screening for FATP mutations in humans with metabolic disorders, whereas knowledge of its expression pattern and factors regulating its expression could be of importance in understanding its biology.

Atherosclerosis, 1997

Posters Apolipoproteins was a strong positive correlation between apoB4s synthesis, degradation a... more Posters Apolipoproteins was a strong positive correlation between apoB4s synthesis, degradation and output as VLDL.

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2015

Archives de Pédiatrie, 2014

The Journal of endocrinology, 1999

Peroxisome proliferator-activated receptor gamma (PPARgamma), a fatty acid-activated nuclear rece... more Peroxisome proliferator-activated receptor gamma (PPARgamma), a fatty acid-activated nuclear receptor, is implicated in adipocyte differentiation and insulin sensitisation. In view of the association of dietary fat intake and bowel disease, the expression of PPARgamma in rodent and human intestine was studied. Expression of PPARgamma mRNA was examined by Northern blot hybridisation, RNase protection, and/or competitive RT-PCR assays, whereas PPARgamma protein levels were evaluated by immunoblotting and immunohistochemistry. PPARgamma mRNA and protein were abundantly expressed in colon relative to the small intestine both in rodents and in man. Interestingly, expression of PPARgamma was primarily localised in the more differentiated epithelial cells in the colon. The level of expression of PPARgamma in colon was similar to the levels seen in adipose tissue. Expression of PPARgamma increased from proximal to distal segments of the colon in man. In Caco-2 and HT-29 human adenocarcinoma...

Nature medicine, 1998

The development of colorectal cancer, one of the most frequent cancers, is influenced by prostagl... more The development of colorectal cancer, one of the most frequent cancers, is influenced by prostaglandins and fatty acids. Decreased prostaglandin production, seen in mice with mutations in the cyclooxygenase 2 gene or in animals and humans treated with cyclooxygenase inhibitors, prevents or attenuates colon cancer development. There is also a strong correlation between the intake of fatty acids from animal origin and colon cancer. Therefore, the peroxisome proliferator-activated receptor gamma (PPARgamma), a downstream transcriptional mediator for prostaglandins and fatty acids which is highly expressed in the colon may be involved in this process. Activation of PPARgamma by two different synthetic agonists increased the frequency and size of colon tumors in C57BL/6J-APCMin/+ mice, an animal model susceptible to intestinal neoplasia. Tumor frequency was only increased in the colon, and did not change in the small intestine, coinciding with the colon-restricted expression of PPARgamma...

European Journal of Biochemistry, 1999

In rodents, cholesterol for adrenal steroidogenesis is derived mainly from high-density lipoprote... more In rodents, cholesterol for adrenal steroidogenesis is derived mainly from high-density lipoproteins (HDL) via the HDL receptor, scavenger receptor-BI (SR-BI). In humans cholesterol for steroidogenesis is considered to be derived from the low-density lipoprotein (LDL) receptor pathway, and the contribution of SR-BI to that is unknown. In the present study SR-BI expression and regulation by steroidogenic stimuli was analysed in human adrenocortical cells and compared with LDL receptor expression. In addition, the functional contribution of both receptors for cholesteryl ester delivery to human adrenocortical cells was compared. Northern blot and reverse transcription-PCR amplification and sequence analysis demonstrated the presence of SR-BI mRNA in foetal and adult human adrenal cortex. Furthermore, SR-BI mRNA was expressed to similar levels in human primary adrenocortical and adrenocortical carcinoma NCI-H295 cells, indicating its presence in the steroid-producing cells. Treatment of NCI-H295 cells with 8Br-cAMP, a stimulator of glucocorticoid synthesis via the protein kinase A second messenger signal transduction pathway, resulted in an increase of both SR-BI and LDL receptor mRNA levels in a time- and dose-dependent manner. The induction of SR-BI and LDL receptor by cAMP was independent of ongoing protein synthesis and occurred at the transcriptional level. Ligand blot experiments indicated that a protein of similar size to SR-BI is the major HDL-binding protein in NCI-H295 cells. Western blot analysis demonstrated that cAMP treatment increased the levels of LDL receptor and, to a lesser extent, SR-BI protein in NCI-H295 cells. Binding and uptake of cholesterol was quantitatively smaller from HDL than from LDL, both in basal as well as in cAMP-stimulated cells. Scatchard analysis under basal conditions indicated that NCI-H295 cells express twice as many specific binding sites for LDL than for HDL. Dissociation constant values (Kd; in nm) were approximately five times higher for HDL than for LDL, indicating a lower affinity of HDL compared with LDL. The combined effects of these two parameters and the low cholesteryl ester content of HDL subfraction 3 (HDL3) contributes to a lower cholesteryl ester uptake from HDL than from LDL by the NCI-H295 cells. In conclusion, both the SR-BI and LDL receptor genes are expressed in the human adrenal cortex and coordinately regulated by activators of glucocorticoid synthesis. In contrast to rodents, in human adrenocortical cells the HDL pathway of cholesterol delivery appears to be of lesser importance than the LDL pathway. Nevertheless, the SR-BI pathway may become of major importance in conditions of functional defects in the LDL receptor pathway.

Proceedings of the National Academy of Sciences, 1998

Journal of Biological Chemistry, 1998

Peroxisome proliferator-activated receptors (PPARs) have been implicated in metabolic diseases, s... more Peroxisome proliferator-activated receptors (PPARs) have been implicated in metabolic diseases, such as obesity, diabetes, and atherosclerosis, due to their activity in liver and adipose tissue on genes involved in lipid and glucose homeostasis. Here, we show that the PPARalpha and PPARgamma forms are expressed in differentiated human monocyte-derived macrophages, which participate in inflammation control and atherosclerotic plaque formation. Whereas PPARalpha is already present in undifferentiated monocytes, PPARgamma expression is induced upon differentiation into macrophages. Immunocytochemistry analysis demonstrates that PPARalpha resides constitutively in the cytoplasm, whereas PPARgamma is predominantly nuclear localized. Transient transfection experiments indicate that PPARalpha and PPARgamma are transcriptionally active after ligand stimulation. Ligand activation of PPARgamma, but not of PPARalpha, results in apoptosis induction of unactivated differentiated macrophages as measured by the TUNEL assay and the appearance of the active proteolytic subunits of the cell death protease caspase-3. However, both PPARalpha and PPARgamma ligands induce apoptosis of macrophages activated with tumor necrosis factor alpha/interferon gamma. Finally, PPARgamma inhibits the transcriptional activity of the NFkappaB p65/RelA subunit, suggesting that PPAR activators induce macrophage apoptosis by negatively interfering with the anti-apoptotic NFkappaB signaling pathway. These data demonstrate a novel function of PPAR in human macrophages with likely consequences in inflammation and atherosclerosis.

Journal of Biological Chemistry, 1997

Apolipoprotein (apo) E, a constituent of several lipoproteins, is a ligand for the low density li... more Apolipoprotein (apo) E, a constituent of several lipoproteins, is a ligand for the low density lipoprotein receptor, and this interaction is important for maintaining cholesterol and triglyceride homeostasis. We have used a gene replacement strategy to generate mice that express the human apoE3 isoform in place of the mouse protein. The levels of apoE mRNA in various tissues are virtually the same in the human apoE3 homozygous (3/3) mice and their littermates having the wild type mouse allele (؉/؉). Total cholesterol and triglyceride levels in fasted plasma from the 3/3 mice were not different from those in the ؉/؉ mice, when maintained on a normal (low fat) chow diet. We found, however, notable differences in the distribution of plasma lipoproteins and apolipoprotein E between the two groups: ␤-migrating lipoproteins and plasma apoB100 levels are decreased in the 3/3 mice, and the apoE distribution is shifted from high density lipoproteins to larger lipoprotein particles. In addition, the fractional catabolic rate of exogenously administered remnant particles without apoE was 6-fold slower in the 3/3 mice compared with the ؉/؉ mice. When the 3/3 and ؉/؉ animals were fed a high fat/high cholesterol diet, the 3/3 animals responded with a dramatic increase (5-fold) in total cholesterol compared with the ؉/؉ mice (1.5-fold), and after 12 weeks on this same diet the 3/3 animals developed significantly (at least 13-fold) larger atherosclerotic plaques in the aortic sinus area than the ؉/؉ animals. Thus the structural differences between human APOE3 and mouse ApoE proteins are sufficient to cause an increased susceptibility to dietary-induced hypercholesterolemia and atherosclerosis in the 3/3 mice.

Journal of Biological Chemistry, 1997

ApoC-III overexpression in mice results in severe hypertriglyceridemia due primarily to a delay i... more ApoC-III overexpression in mice results in severe hypertriglyceridemia due primarily to a delay in the clearance of triglyceride-rich lipoproteins. We have, in primary cultures of rat hepatocytes, characterized a lipolysis-stimulated receptor (LSR). The apparent number of LSR that are available on rat liver plasma membranes is negatively correlated with plasma triglyceride concentrations measured in the fed state. We therefore proposed that the primary physiological role of the LSR is to contribute to the cellular uptake of triglyceriderich lipoproteins. We have now tested the effect of apoC-III on the binding of triglyceride-rich lipoproteins to LSR. Supplementation of 125 I-very low density lipoprotein (VLDL) with apoC-III inhibited the LSR-mediated binding, internalization, and degradation of 125 I-VLDL in primary cultures of rat hepatocytes. Studies using isolated rat liver plasma membranes showed that enrichment of human VLDL and chylomicrons with synthetic or purified human apoC-III decreased their binding to the LSR by about 40%. Supplementation of triglyceride-rich lipoproteins under the same conditions with human apoC-II had no such inhibitory effect, despite the fact that this apoprotein bound as efficiently as apoC-III to these particles.

Genomics, 2000

Uptake of fatty acids into cells is a controlled process in part regulated by fatty acid transpor... more Uptake of fatty acids into cells is a controlled process in part regulated by fatty acid transport proteins (FATPs), which facilitate the transport of fatty acids across the cell membrane. In this study the structure of the human FATP-1 (HGMW-approved symbol SLC27A1) cDNA and gene was determined, and the expression of its mRNA in human was characterized. Muscle and adipose tissue have the highest levels of FATP-1 mRNA, small intestine has intermediate levels, and FATP-1 mRNA is barely detectable in liver. The human FATP-1 gene has 12 exons and extends over more than 13 kb of genomic DNA. The FATP gene maps to chromosome 19p13.1 by fluorescence in situ hybridization, a region previously suggested to be implicated in the determination of small dense low-density lipoprotein (LDL). Knowledge of the gene structure and chromosomal localization will allow screening for FATP mutations in humans with metabolic disorders, whereas knowledge of its expression pattern and factors regulating its expression could be of importance in understanding its biology.

Atherosclerosis, 1997

Posters Apolipoproteins was a strong positive correlation between apoB4s synthesis, degradation a... more Posters Apolipoproteins was a strong positive correlation between apoB4s synthesis, degradation and output as VLDL.