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Biomedical subjects

D Gospodarowicz

Publications and source records attributed to D Gospodarowicz.

At least 91 records · Page 5Linked to original sources
PubMed1985

Acidic fibroblast growth factor (FGF) from bovine brain: amino-terminal sequence and comparison with basic FGF.

Acidic fibroblast growth factor (FGF) from bovine brain has been isolated by a combination of salt precipitation, ion-exchange chromatography, heparin-Sepharose affinity chromatography and reverse phase h.p.l.c. The amino acid composition of the mitogen is indistinguishable from that of acidic FGF previously purified. The amino-terminal sequence of acidic FGF was established as Phe-Asn-Leu- Pro-Gly-Asn-Tyr-Lys-Pro-Lys-Leu-X-Tyr-X-Ser-Asn-Gly-X-Tyr-Phe-Leu-Arg-Il e-Leu-Pro-Asp-Gly. Acidic FGF is structurally different from basic FGF as judged by mol. wt., amino acid composition and sequence. In vitro biological comparison of the two growth factors indicates that acidic and basic FGFs possess the same intrinsic activities to stimulate the proliferation of aorta, vein or capillary endothelial cells and adrenal cortex cells, but acidic FGF is 30-100 times less potent, depending on the cell type.

Amino Acid Sequence↗
PubMed1985

Isolation of pituitary fibroblast growth factor by fast protein liquid chromatography (FPLC): partial chemical and biological characterization.

Bovine pituitary fibroblast growth factor has been purified 222,000-fold to homogeneity by a combination of differential salt extraction, gel filtration, and ion exchange chromatography on Mono S column. Pituitary FGF is a single-chain polypeptide with an apparent molecular mass of 15,800 and an isoelectric point of 9.6. It is highly active in triggering the proliferation of bovine and human vascular endothelial cell [half-maximal stimulation at 23-40 pg/ml (1.5-2.6 pM) and saturation between 140 and 280 pg/ml (9.3-18.6 pM)]. It displays a similar activity on bovine vascular smooth muscle cells, corneal endothelial cells, granulosa and adrenal cortex cells, and rabbit costal chondrocytes.

Animals↗
PubMed1985

Biotin and choline replace the growth requirement of Madin-Darby canine kidney cells for high-density lipoproteins.

MDCK cells maintained on extracellular matrix (ECM)-coated dishes and exposed to Dulbecco's modified Eagle's medium (DME) supplemented with transferrin and either high-density lipoproteins (HDLs) or phosphatidyl choline (PC) liposomes have a growth rate and final cell density similar to those of cultures exposed to serum-supplemented DME. When MDCK cells are exposed to a medium consisting of a mixture (1:1) of DME and F12 medium (D/F), the addition of transferrin (10 micrograms/ml) alone supports cell growth and the presence of HDLs or PC liposomes is no longer required. MDCK cells exposed to D/F medium supplemented with transferrin can be passaged for more than 50 generations in total absence of serum. The F12 components that support growth in the absence of HDLs or PC liposomes are biotin (which is absent in DME) and choline (which is present in insufficient concentration in DME). Supplementation of DME with transferrin, biotin (3.6 ng/ml), and choline (10 micrograms/ml) allows optimal growth of MDCK cells and permits serial propagation through more than 50 generations. The growth requirement of MDCK cells for HDLs or PC liposomes can therefore be replaced by adequate concentrations of biotin and choline. The widely observed fact that a combination of DME/F12 medium is more effective than DME alone in supporting cell growth may be due in part to the lack of biotin and suboptimal choline concentration in DME.

Animals↗
PubMed1985

Primary structure of bovine pituitary basic fibroblast growth factor (FGF) and comparison with the amino-terminal sequence of bovine brain acidic FGF.

The two major mitogenic polypeptides for endothelial cells have been purified to homogeneity. The complete primary structure of bovine pituitary basic fibroblast growth factor (FGF) and the amino-terminal amino acid sequence of bovine brain acidic FGF have been established by gas-phase sequence analyses. Homogeneous preparations of these polypeptides are potent mitogens (basic FGF, ED50 approximately equal to 60 pg/ml; acidic FGF ED50 approximately equal to 6000 pg/ml) for many diverse cell types including capillary endothelial cells, vascular smooth muscle cells, and adrenocortical and granulosa cells; in vivo, basic FGF is a powerful angiogenic agent in the chick chorioallantoic membrane assay. The available protein sequence data demonstrate the existence of significant structural homology between the two polypeptides.

Amino Acid Sequence↗
PubMed1985

Sulfated proteoglycan synthesis by confluent cultures of rabbit costal chondrocytes grown in the presence of fibroblast growth factor.

We examined the effect of fibroblast growth factor (FGF) on proteoglycan synthesis by rabbit costal chondrocyte cultures maintained on plastic tissue culture dishes. Low density rabbit costal chondrocyte cultures grown in the absence of FGF gave rise at confluency to a heterogeneous cell population composed of fibroblastic cells and poorly differentiated chondrocytes. When similar cultures were grown in the presence of FGF, the confluent cultures organized into a homogenous cartilage-like tissue composed of rounded cells surrounded by a refractile matrix. The cell ultrastructure and that of the pericellular matrix were similar to those seen in vivo. The expression of the cartilage phenotype in confluent chondrocyte cultures grown from the sparse stage in the presence vs. absence of FGF was reflected by a fivefold increase in the rate of incorporation of [35S]sulfate into proteoglycans. These FGF effects were only observed when FGF was present during the cell logarithmic growth phase, but not when it was added after chondrocyte cultures became confluent. High molecular weight, chondroitin sulfate proteoglycans synthesized by confluent chondrocyte cultures grown in the presence of FGF were slightly larger in size than that produced by confluent cultures grown in the absence of FGF. The major sulfated glycosaminoglycans associated with low molecular weight proteoglycan in FGF-exposed cultures were chondroitin sulfate, while in cultures not exposed to FGF they were chondroitin sulfate and dermatan sulfate. Regardless of whether or not cells were grown in the presence or absence of FGF, the 6S/4S disaccharide ratio of chondroitin sulfate chains associated with high and low molecular weight proteoglycans synthesized by confluent cultures was the same. These results provide evidence that when low density chondrocyte cultures maintained on plastic tissue culture dishes are grown in the presence of FGF, it results in a stimulation of the expression and stabilization of the chondrocyte phenotype once cultures become confluent.

Animals↗
PubMed1985

Effect of exogenous extracellular matrices on proteoglycan synthesis by cultured rabbit costal chondrocytes.

We examined the effect of an extracellular matrix (ECM), produced by either bovine corneal endothelial (BCE) cells or mouse PF HR-9 teratocarcinoma cells, on the ability of rabbit costal chondrocytes to re-express their phenotype once confluent. Rabbit chondrocytes seeded at low densities and grown on plastic tissue culture dishes produced a heterogeneous cell population composed of both overtly differentiated and poorly differentiated chondrocytes, as well as fibroblastic cells. On the other hand, cultures grown on BCE-ECM- or HR-9-ECM-coated dishes reorganized into a homogeneous cartilage-like tissue composed of round cells surrounded by a refractile matrix that stained intensely with alcian green. The cell ultrastructure and that of their pericellular matrix were similar to those seen in vivo. The differentiation of chondrocyte cultures grown on the ECMs vs. plastic was reflected by a two- to three-fold increase in the maximal rate of incorporation of [35S]sulfate and [3H]glucosamine into proteoglycans. Furthermore, the ratio of 35S-labeled proteoglycans incorporated in the cell layer vs. those released into the medium was 1.5-2.5-fold higher when cultures were grown on the ECMs than on plastic. This suggests that the ECMs stimulate the incorporation of newly synthesized proteoglycans into a cartilaginous matrix. Since chondrocyte cultures grown on BCE-ECM or HR-9-ECM give rise to a homogeneous cartilage-like tissue even when seeded at low cell densities, they provide a model for the study of cell-substrate interactions that are responsible for the maintenance of the differentiated phenotype of chondrocytes.

Animals↗
PubMed1985

Corpus luteum angiogenic factor is related to fibroblast growth factor.

An angiogenic growth factor present in bovine corpus luteum (CL) has been purified to apparent homogeneity by a combination of differential salt precipitation, ion exchange chromatography, and heparin-Sepharose chromatography. It is a single chain polypeptide with an apparent mol wt of 15,000 and an amino acid composition similar to that previously reported for pituitary and brain fibroblast growth factor (FGF). Sequence analysis of the first 17 residues of the CL-derived growth factor identified the sequence; His-Phe-Lys-Asp-Pro-Lys-Arg-Leu-Tyr-X-Lys-Asn-Gly-Gly-X-Phe-Leu. This sequence is identical to residues 16-33 of bovine pituitary and brain FGF, indicating that the CL-derived growth factor is an amino-terminally truncated form of FGF and is otherwise similar, if not identical, to FGF. The biological activity of CL FGF is indistinguishable from that of pituitary or brain FGF. It is highly active in triggering the proliferation of cultured bovine vascular endothelial cells derived either from large vessels (aortic arch) or from corpus luteum and adrenal cortex capillaries (half-maximal stimulation at 20-40 pg/ml and saturation at 400-600 pg/ml). In vivo implants containing 50 ng to 1 microgram CL-derived growth factor stimulate neovascularization in the chorioallantoic membrane of the chick embryo. In addition to being mitogenic for vascular endothelial cells, CL FGF also stimulates the proliferation of a wide variety of mesoderm- and neuroectoderm-derived cells, including vascular smooth muscle cells, granulosa and adrenal cortex cells, rabbit costal chondrocytes, and corneal endothelial cells.

Allantois↗
PubMed1984

Effect of p-nitrophenyl-beta-D-xyloside on proteoglycan synthesis and extracellular matrix formation by bovine corneal endothelial cell cultures.

The effect of p-nitrophenyl-beta-D-xyloside on proteoglycan synthesis and extracellular matrix (ECM) formation by cultured bovine corneal endothelial (BCE) cells was investigated. BCE cells actively proliferating on plastic dishes produced in the absence of xyloside an ECM containing various proteoglycans. Heparan sulfate was the main 35S-labeled glycosaminoglycan component (83%). Dermatan sulfate (14%) and chondroitin sulfate (3%) were also present. Exposure of actively proliferating BCE cells to xyloside totally inhibited synthesis of proteoglycans containing dermatan sulfate or chondroitin sulfate and caused an 86% inhibition of heparan sulfate proteoglycan synthesis. The heparan sulfate proteoglycans that were extracted from the ECM produced by BCE cells exposed to xyloside had a smaller size and a reduced charge density compared to their counterparts extracted from the ECM of cultures not exposed to xyloside. In contrast to the inhibitory effect of the xyloside on proteoglycan synthesis, exposure of actively proliferating BCE cells to xyloside stimulated synthesis of free chondroitin sulfate and heparan sulfate chains. All of the xyloside-initiated glycosaminoglycan chains were secreted into the culture medium. The proteoglycan-depleted matrices produced by BCE cells exposed to xyloside were used to study the effect of these matrices on proteoglycan synthesis by BCE cells. BCE cells growing on proteoglycan-depleted ECM showed a considerable increase in the rate of proteoglycan synthesis compared to BCE cells growing on normal ECM. Moreover, the pattern of glycosaminoglycan synthesis by BCE cells growing on proteoglycan-depleted ECM was changed to one which resembled that of BCE cells actively proliferating on plastic dishes. It is postulated that BCE cells are able to recognize when an ECM is depleted of proteoglycan and to respond to it by increasing their rate of proteoglycan synthesis and incorporation into the ECM.

Animals↗
PubMed1984

Growth requirements of low-density rabbit costal chondrocyte cultures maintained in serum-free medium.

The factors required for the active proliferation of low-density rabbit costal chondrocytes exposed to 9:1 (v/v) mixture of Dulbecco's modified Eagle's medium and Ham's F12 medium have been defined. Low-density primary cultures of rabbit costal chondrocytes proliferated actively when the medium was supplemented with high-density lipoprotein (300 micrograms/ml), transferrin (60 micrograms/ml), fibroblast growth factor (FGF) (1 ng/ml), hydrocortisone (10(-6) M), and epidermal growth factor (EGF) (30 ng/ml). Insulin, although it slightly decreased the final cell density, was required for reexpression of the cartilage phenotype at confluence. Optimal proliferation of low-density chondrocyte cultures was only observed when dishes were coated with an extracellular matrix (ECM) produced by cultured corneal endothelial cells, but not on plastic. Furthermore, serum-free chondrocyte cultures seeded at low density and maintained on ECM-coated dishes gave rise to a homogeneous cartilage-like tissue composed of spherical cells. These chondrocytes therefore seem to provide a good experimental system for analyzing factors involved in supporting proliferation of chondrocytes and their phenotypic expression.

Animals↗
PubMed1984

Isolation and partial molecular characterization of pituitary fibroblast growth factor.

Fibroblast growth factor (FGF) has been purified to homogeneity from bovine pituitaries by two methods. Starting material for both methods was an FGF preparation partially purified as described by Gospodarowicz [Gospodarowicz, D. (1975) J. Biol. Chem. 250, 2515-2520]. Purification procedure I involved cation-exchange and reversed-phase HPLC, while procedure II employed gel filtration and ion-exchange chromatography. Isolation was monitored by testing column fractions for their capacity to stimulate the proliferation of vascular endothelial cells in vitro. The growth factor has an approximate molecular weight of 16,000. Its amino-terminal sequence was determined as Pro-Ala-Leu-Pro-Glu-Asp-Gly-Gly-Ser-Gly-Ala-Phe-Pro-Pro-Gly. Sequence and amino acid composition indicate that the structure of pituitary FGF is different from that of other known growth factors. Pituitary FGF, as isolated under nonacidic conditions (procedure II), has high potency and intrinsic activity to stimulate adult bovine aortic endothelial cells (half-maximal proliferation at 2 pM). Acidic conditions as in procedure I, however, lead to about 90% loss of potency while the intrinsic activity remains intact (identical maximal stimulation values). By all other criteria (molecular weight, amino acid composition, amino-terminal sequence), the two preparations are indistinguishable. Antibodies were raised in rabbits against a synthetic peptide representing the first nine residues of the amino-terminal sequence of the pituitary FGF. The polyclonal antibodies recognize the synthetic peptide and the purified growth factor on an equimolar basis and are capable of inhibiting mitogenic activity in vitro. This report describes a partial chemical characterization of a pituitary FGF and demonstrates rigorously that the characterized protein possesses the mitogenic activity commonly referred to as "basic pituitary FGF."

Amino Acid Sequence↗
PubMed1984

Isolation of brain fibroblast growth factor by heparin-Sepharose affinity chromatography: identity with pituitary fibroblast growth factor.

Brain and pituitary fibroblast growth factors (FGF) have been purified to apparent homogeneity from crude tissue extracts by a three-step procedure, including salt precipitation, ion-exchange chromatography, and heparin-Sepharose affinity chromatography. Brain and pituitary FGF have similar amino acid compositions and are indistinguishable with respect to molecular weight (16,000 by polyacrylamide gel electrophoresis), retention behavior in reversed-phase high-performance liquid chromatography, and recognition by antibodies directed against the amino-terminal sequence of pituitary FGF. Brain FGF preparations purified by heparin-Sepharose contain, in addition to the major FGF molecular species, at least two additional forms of the growth factor, which appear to be very similar by all the above criteria, except for retention in high-performance liquid chromatography.

Animals↗
PubMed1984

Comparison of the ability of basement membranes produced by corneal endothelial and mouse-derived Endodermal PF-HR-9 cells to support the proliferation and differentiation of bovine kidney tubule epithelial cells in vitro.

The proliferation and morphological differentiation of bovine kidney collecting-tubule epithelial cells has been examined as a function of substrata and plasma factors. Collecting kidney tubule explant maintained in vitro gave rise to two distinct cell populations; one was composed mostly of fibroblastic cells whereas the other was epithelioid (EP cells). The proliferation of fibroblastic cells when exposed to serum-supplemented medium was best expressed when cells were maintained on a basement membrane produced by bovine corneal endothelial cells. This basement membrane has a composition, which in previous studies has been shown to favor the proliferation of mesenchymal cells. In contrast, the proliferation of EP cells was best expressed when cells were maintained on a basement membrane produced by the mouse-derived endodermal cell line PF-HR-9 (HR-9-BM). This basement membrane has a biochemical composition very similar to the basement membrane underlying the kidney tubules. Although the fibroblast confluent monolayer maintained on bovine corneal endothelial cell extracellular matrix did not undergo morphogenesis, the confluent monolayer of EP cells maintained on HR-9-BM shows hemicyst formation, suggesting that they were capable of vectorial fluid transport. They also built a complex three-dimensional kidney tubulelike network. Some tubules became grossly visible and floated into the tissue culture medium, remaining tethered to the cell monolayer at either end of the tubule. On an ultrastructural level, the tubules consisted of cells held together with junctional complexes arranged so as to form a lumen. The smallest lumen were bordered by 2-3 cells, and the largest ones by 8-15 cells. The lumens of the larger tubules did contain granular fibrillar and amorphous debris. Low-density EP cell cultures maintained on HR-9-BM could be induced to proliferate at a rate approaching that of cultures exposed to serum when they were exposed to medium supplemented with high-density lipoprotein (HDL, 750 micrograms protein/ml) and transferrin (50 micrograms/ml). When exposed to HDL concentrations equal or lower than 250 micrograms protein/ml, low-density cultures proliferated at a slow rate and readily formed tubulelike structures. This observation indicates that EP cells do not need to reach confluence to undergo morphogenesis, and that HDL, which in the presence of transferrin supports the cell proliferation, can favor their differentiation into tubulelike structures once its concentration becomes limiting for mitogenesis.

Animals↗
PubMed1984

Permissive effect of insulin on the adenosine 3',5'-monophosphate-dependent up-regulation of low density lipoprotein receptors and the stimulation of steroid release in bovine adrenal cortical cells.

Bovine adrenal cortical cells growth on extracellular matrix-coated dishes in the presence of F-12 medium supplemented with high density lipoprotein (30 micrograms protein/ml), insulin (50 ng/ml), transferrin (1 microgram/ml), and fibroblast growth factor (100 ng/ml) expressed high affinity low density lipoprotein (LDL) receptors (Kd = 2.0 X 10(-8) M) present at a density of 3 X 10(4) receptors/cell. The density of LDL receptors per cell could be increased 3-fold (9 X 10(4) receptors/cell) by incubating the cells for 24 h with cholera toxin (CT; 10 ng/ml), but not with insulin (100 ng/ml). This correlated with increased LDL internalization (10-fold) and degradation (5-fold). 11-Deoxycortisol (11 DOC) release was increased by 2.7-fold. The addition of insulin (100 ng/ml) together with CT (10 ng/ml) markedly potentiated the effects of CT on LDL binding, internalization, and degradation as well as on steroid release. Preincubation (24 h) of the cells with insulin (100 ng/ml) together with CT resulted in a 12.7-fold increase in high affinity LDL receptor density (3.6 X 10(5) receptors/cell), while LDL internalization and degradation were increased by 45- and 22-fold, respectively. This correlated with a 9.6-fold increase in the 11 DOC released into the medium. The effects of insulin on the induction of high affinity LDL receptors as well as increased internalization and degradation of [125I]LDL were both time and concentration dependent in cultures exposed to CT. Secretion of 11 DOC paralleled in a time-dependent manner the amount of internalized [125I]LDL. Exposure of the cells to chloroquine (100 microM) resulted in a 95% inhibition of [125I]LDL degradation correlating with an 80% decrease in 11 DOC released in cells preexposed to CT and insulin. The results of these studies suggest that in bovine adrenal cortex cells grown in chemically defined medium, insulin modulates steroidogenic cAMP-induced response by increasing both the LDL receptor pathway activity and 11 DOC release.

Adrenal Cortex↗
PubMed1984

Extracellular matrix (ECM) proteoglycans produced by cultured bovine corneal endothelial cells.

The nature of the proteoglycan(s) (PG) found in the extracellular matrix (ECM) layer produced by cultured bovine corneal endothelial (BCE) cells is analyzed. The PG(s) account for approximately 5 to 6% of the dry weight of the ECM, regardless of the amount of extracellular soluble PG available in the medium. A 4 M guanidinium chloride (GuCl) extract of ECM was separated on a dissociative cesium chloride (CsCl) gradient (1.25 g/cm3 starting density). Results showed one main peak of PG substance(s) comprising 91% of the total labelled substance and uronic acid, banding at a specific buoyant density of 1.29 g/cm3. The molecular weight of this major PG(s) as estimated by gel filtration on Sepharose CL-4B ranged from 0.5 to 0.7 X 10(6). Further chemical analysis of the main PG(s) band revealed a protein moiety accounting for 45% of the weight and carbohydrates-glycosaminoglycans (GAG) accounting for the remaining 55%. Analysis of the GAG chains (over the entire gradient) showed a composition, based on the susceptibility of the PG substance(s) to degrading enzymes, of 50% heparan sulfate, 43.5% dermatan sulfate, and 6.5% chondroitin 4- and 6-sulfate chains. BCE cell cultures grown in the presence of beta-D-xyloside produced an ECM lacking more than 90% of the GAG content found in the control ECM. The medium-soluble GAG chains, produced in vast excess in cultures grown in the presence of beta-D-xyloside, are composed mainly of chondroitin 4- and 6-sulfates.

Animals↗
PubMed1983

Brain-derived fibroblast growth factor: a study of its inactivation.

Brain fibroblast growth factor has been identified as a component of myelin basic protein. Its activity is destroyed when treated with a variety of solvents including dilute acid, organic solvents and solutions of guanidine hydrochloride. These conditions do not alter the encephalitogenic properties of myelin basic protein.

Animals↗
PubMed1983

Are factors originating from serum, plasma, or cultured cells involved in the growth-promoting effect of the extracellular matrix produced by cultured bovine corneal endothelial cells?

The possibilities that the growth-promoting effect of the extracellular matrix (ECM) produced by cultured bovine corneal endothelial (BCE) cells could be due to: (1) adsorbed cellular factors released during the cell lysis process leading to the denudation of the ECM; (2) adsorbed serum or plasma factors: or (3) adsorbed exogenous growth factors have been examined. Exposure of confluent BCE cultures to 2 M urea in medium supplemented with 0.5% calf serum denudes the ECM without cell lysis. The ECM prepared by this procedure supports cell growth just as well as ECM prepared by denudation involving cell lysis. Thus, it is unlikely that the growth-promoting properties of ECM are due to adsorbed cellular factors. When the ECM produced by BCE cells grown in defined medium supplemented with high-density lipoprotein, transferrin, and insulin was compared to the ECMs produced by cells grown in the presence of serum- or plasma-supplemented medium, all were found to be equally potent in stimulating cell growth. It is therefore unlikely that the growth-promoting ability of the ECM is due to adsorbed plasma or serum components. When fibroblast growth factor (FGF)-coated and ECM-coated plastic dishes were submitted to a heat treatment (70 degrees C, 30 min) which results in the inactivation of FGF, the growth-supporting ability of FGF-coated dishes was lost, while the comparable ability of ECM-coated dishes was not affected significantly. This observation tends to demonstrate that the active factor present in the ECM is not FGF. Nor is it platelet-derived growth factor (PDGF), since treatment known to destroy the activity of PDGF, such as exposure to dithiothreitol (0.1 M, 30 min, 22 degrees C) or to beta-mercaptoethanol (10%) in the presence or absence of 6 M urea for 30 min at 22 degrees C, does not affect the growth-promoting activity of ECM. It is therefore unlikely that the growth-promoting effect of ECM is due to cellular growth-promoting agents or to plasma or serum factors adsorbed onto the ECM.

Adsorption↗
PubMed1983

Phosphatidyl choline and the growth in serum-free medium of vascular endothelial and smooth muscle cells, and corneal endothelial cells.

Liposomes made by sonication of egg yolk phosphatidyl choline support the proliferation of low-density bovine vascular and corneal endothelial cells, and vascular smooth muscle cells maintained on basement laminacoated dishes and exposed to a defined medium supplemented with transferrin. The optimal growth-promoting effect of phosphatidyl choline was observed at concentrations of 25 micrograms/ml for low-density cultures of vascular smooth muscle cells, and 100 micrograms/ml for vascular and corneal endothelial cells. The growth rate and final cell density of vascular endothelial cells exposed to a synthetic medium supplemented with transferrin and either high-density lipoproteins or phosphatidyl choline has been compared. Although cultures exposed to phosphatidyl choline reached a final cell density similar to that of cultures exposed to high-density lipoproteins, they had a longer average doubling time (17 h vs. 12 h) during their logarithmic growth phase and a shorter lifespan (17 generations vs. 30 generations). Similar observations were made in the case of vascular smooth muscle cells or bovine corneal endothelial cells maintained in medium supplemented with transferrin, fibroblast growth factor (FGF) or epidermal growth factor (EGF), and insulin and exposed to either high-density lipoproteins or phosphatidyl choline. Since phosphatidyl choline can, for the most part, replace high-density lipoproteins in supporting the proliferation of various cell types, it is likely that the growth stimulating signal conveyed by high-density lipoproteins is associated with its polar lipid fraction, which is composed mostly of phosphatidyl cholines.

Animals↗