Changes in glycosaminoglycans during the neuritogenesis in PC12 pheochromocytoma cells induced by nerve growth factor

Cellular differentiation assessments by measuring the degree of cellular internalization and membrane adsorption using designed peptides

We demonstrate examples of cellular differentiation assessments, including cellular neurite outgrowth and fat cell maturation, by measuring the degree of membrane adsorption or cellular internalization using designed peptides. Because changes in the cellular membrane and cytosol during differentiation were shown to influence membrane adsorption and cellular internalization, we could successfully evaluate the extent of differentiation simply like stain indicators.

Voltage-gated K+ channels play a role in cAMP-stimulated neuritogenesis in mouse neuroblastoma N2A cells

Neuritogenesis is essential in establishing the neuronal circuitry. An important intracellular signal causing neuritogenesis is cAMP. In this report, we showed that an increase in intracellular cAMP stimulated neuritogenesis in neuroblastoma N2A cells via a PKA-dependent pathway. Two voltage-gated K(+) (Kv) channel blockers, 4-aminopyridine (4-AP) and tetraethylammonium (TEA), inhibited cAMP-stimulated neuritogenesis in N2A cells in a concentration-dependent manner that remarkably matched their ability to inhibit Kv currents in these cells. Consistently, siRNA knock down of Kv1.1, Kv1.4, and Kv2.1 expression reduced Kv currents and inhibited cAMP-stimulated neuritogenesis. Kv1.1, Kv1.4, and Kv2.1 channels were expressed in the cell bodies and neurites as shown by immunohistochemistry. Microfluorimetric imaging of intracellular [K(+)] demonstrated that [K(+)] in neurites was lower than that in the cell body. We also showed that cAMP-stimulated neuritogenesis may not involve voltage-gated Ca(2+) or Na(+) channels. Taken together, the results suggest a role of Kv channels and enhanced K(+) efflux in cAMP/PKA-stimulated neuritogenesis in N2A cells.

TAT-mediated intracellular protein delivery to primary brain cells is dependent on glycosaminoglycan expression

Although some studies have shown that the cell penetrating peptide (CPP) TAT can enter a variety of cell lines with high efficiency, others have observed little or no transduction in vivo or in vitro under conditions mimicking the in vivo environment. The mechanisms underlying TAT-mediated transduction have been investigated in cell lines, but not in primary brain cells. In this study we demonstrate that transduction of a green fluorescent protein (GFP)-TAT fusion protein is dependent on glycosaminoglycan (GAG) expression in both the PC12 cell line and primary astrocytes. GFP-TAT transduced PC12 cells and did so with even higher efficiency following NGF differentiation. In cultures of primary brain cells, TAT significantly enhanced GFP delivery into astrocytes grown under different conditions: (1) monocultures grown in serum-containing medium; (2) monocultures grown in serum-free medium; (3) cocultures with neurons in serum-free medium. The efficiency of GFP-TAT transduction was significantly higher in the monocultures than in the cocultures. The GFP-TAT construct did not significantly enter neurons. Experimental modulation of GAG content correlated with alterations in TAT transduction in PC12 cells and astrocyte monocultures grown in the presence of serum. In addition, this correlation was predictive of TAT-mediated transduction in astrocyte monocultures grown in serum free medium and in coculture. We conclude that culture conditions affect cellular GAG expression, which in turn dictates TAT-mediated transduction efficiency, extending previous results from cell lines to primary cells. These results highlight the cell-type and phenotype-dependence of TAT-mediated transduction, and underscore the necessity of controlling the phenotype of the target cell in future protein engineering efforts aimed at creating more efficacious CPPs.

Amyloidogenesis: historical and modern observations point to heparan sulfate proteoglycans as a major culprit

Amyloids are complex tissue deposits and each type is identified by one of 22 different proteins or peptides which become re-folded into non-native conformational intermediates and then assemble into fibrils of a highly regular structure. All amyloid deposits also contain apolipoprotein E (apoE) as well as the basement membrane (BM) components, serum amyloid P and heparan sulfate proteoglycans (HSPG), perlecan or agrin. These BM components likely contribute to the overall organization of amyloid fibrils and HSPG has been further implicated in the genesis of amyloid. A growing body of evidence, summarized in this review, suggests that heparan sulfate (HS) promotes fibrillogenesis by associating with the amyloid precursors and inducing the conformational change required for their assembly into fibrils. HS also remains associated with the nascent fibrils contributing to its stability. These activities of HS are likely mediated through specific binding sites on the precursor proteins which appear to have sequence characteristics that are unique to amyloid.

A high-efficiency protein transduction system demonstrating the role of PKA in long-lasting long-term potentiation

Proteins and peptides have been demonstrated to penetrate across the plasma membrane of eukaryotic cells by protein transduction domains. We show that protein transduction by 11 arginine (11R) is an efficient method of delivering proteins into the neurons of brain slices. Here, we demonstrate that PKA inhibitory peptide, fused with 11R and nuclear localization signal, delivers the peptide exclusively into the nuclear compartment of neurons in brain slices. This inhibitory peptide blocked both cAMP responsive element-binding protein phosphorylation and long-lasting long-term potentiation (LTP) induction, but not early LTP. These results highlight transduction of proteins and peptides into specific neuronal subcellular compartments in brain slices as a powerful tool for studying neuronal plasticity.

Chondroitin sulphate proteoglycans in the rat brain: candidates for axon barriers of sensory neurons and the possible modification by laminin of their actions

The addition of chondroitin sulphate proteoglycans (CSPGs), purified from the rat brain, to the culture medium of PC12D cells inhibited their proliferation and neurite outgrowth. Therefore, we investigated the effects of several extracellular components on the inhibitory actions of CSPGs on PC12D cells, as well as their immunocytochemical distribution in the rat embryo to determine whether the findings in vitro could be reproduced in vivo. Coating of the substratum with polylysine was necessary for the appearance of the inhibitory effects of brain CSPGs on PC12D cells. The additional pretreatment of polylysine-coated dishes with laminin or fibronectin promoted the outgrowth of neurites from PC12D cells. Laminin and fibronectin, but not collagen (types I and IV) and CELL-TAK (cell adhesion molecules), prevented the inhibitory effects of brain CSPGs in a concentration-dependent manner. Doses producing 50% reduction by laminin (or fibronectin) of the CSPG effects were 1.5 (or 25) micrograms/ml for neurite outgrowth and 2.2 (or 28) micrograms/ml for proliferation. The ratio of dish-attached CSPGs to laminin necessary for 50% reduction was about approximately 50:1 (wt/wt). Laminin from any source had the same effect. Brain CSPGs also obviously impeded the growth of fibres from dorsal root ganglion explants and primary cultured dorsal root ganglion neurons. Neurocan (a major CSPG in the brain)-like immunoreactivity was detected in the boundary caps and roof plate in the rat embryo at 13.5 days of gestation, when DRG neurons were extending their axons to the neural tube. The distributions of laminin and tenascin appeared, respectively, to be slightly and considerably different from that of neurocan.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chondroitin sulfates with different structures on leukemia cells: U-937 cell proliferation and differentiation

Chondroitin sulfates extracted and purified by different manufacturers were tested to evaluate their effects on proliferation and differentiation processes of U-937 cells. The different chondroitin sulfates were evaluated for purity, structure and physicochemical properties. The three chondroitin sulfates utilized did not present other contaminant glycosaminoglycans and proteins and had about the same relative molecular mass but different disaccharide patterns and charge density. Chondroitin sulfates with small amounts of disulfated disaccharides and low charge density, at 5 micrograms/ml concentration, doubled (about + 133%) cell proliferation in comparison to controls. In contrast, chondroitin sulfates with large amounts of disulfated disaccharides and high sulfate to carboxyl ratio were less effective (about + 15%) in stimulating cell proliferation at low concentration. A decrease of U-937 cell proliferation was observed in proportion to the increased amounts of chondroitin sulfate with low sulfate to carboxyl ratio. On the contrary, chondroitin sulfate with large amounts of disulfated disaccharides produced increased cell proliferation depending on concentration. Small amounts (5-10 micrograms/ml) of chondroitin sulfates with low charge density reduced the differentiative process of U-937 cells. Chondroitin sulfate with large amounts of disulfated disaccharides and high charge density seemed to be able to produce a significant decrease of differentiative processes only at very high concentrations (1000 micrograms/ml). These contrasting effects of chondroitin sulfates with different disaccharide patterns (and structure) and charge density on a leukemia cell line could help to explain the regulation of proliferative and/or differentiative processes of hemopoietic cells. This is underlined by the changes of types, physicochemical properties and structure of glycosaminoglycans induced by different extracellular factors and agents.

Core proteins of soluble chondroitin sulfate proteoglycans purified from the rat brain block the cell cycle of PC12D cells

The effects of soluble chondroitin sulfate proteoglycans (CSPGs) purified from the rat brain on proliferation of and neurite outgrowth from PC12D cells (Katoh-Semba et al., J Neurosci Res 17:36, 1987) were investigated. When PC12D cells are cultured under standard conditions, they proliferate with a doubling time of about 2 days, irrespective of the presence or absence of NGF. However, the addition of a mixture of several types of purified soluble brain CSPG (50 nmol uronic acid/ml) to the culture medium prevented the increase in the number of PC12D cells as well as the nerve growth factor (NGF)-induced neurite extension. The dose for 50% inhibition (ID50) was 1.6 nmol/ml for cell proliferation and 2.7 nmol/ml for neurite elongation. The increase in cell number seemed to stop around 6 h after exposure to culture medium supplemented with brain-derived CSPGs, and even substratum-attached CSPGs were able to exert such inhibitory effects. Only brain-type CSPGs, not a cartilage-derived CSPG (PGH) or a hyaluronate-binding PGH, had such inhibitory effects. Furthermore, these inhibitory activities were associated only with the core proteins of brain-derived CSPGs, and not with polysaccharide chains from brain-derived CSPGs. Incorporation of [3H]thymidine into DNA did not decrease for at least the first 12 h. Consequently, the amount of DNA per cell after 48 h of culture was about twofold higher in cells treated with brain CSPGs than in nontreated cells after exposure to the medium with CSPGs. Microspectrophotometry revealed that the population of cells with a high DNA content was greater in the culture treated with brain-derived CSPGs than in the control culture. These findings indicate that purified soluble brain CSPGs block the cell cycle of PC12D cells at the G2 phase with resultant cessation of cell proliferation and the inhibition of neurite outgrowth.

Nerve growth factor-induced changes in the structure of sulfated proteoglycans in PC12 pheochromocytoma cells

Structural changes in proteoglycans (PGs) were examined during the neuritogenesis of PC12 cells induced by nerve growth factor (NGF). (1) A heparan sulfate (HS) PG and a chondroitin sulfate (CS) PG were synthesized by PC12 cells, irrespective of the presence of NGF or the duration of culture. PGs released from PC12 cells into the culture medium were mostly CSPGs. (2) In the absence of NGF, the apparent molecular mass of HSPG prepared from PC12 cells after 3 days of culture was in the range of 90-190 kDa for the intact form (Kav = 0.38 on Sepharose CL-6B), 12 kDa for HS, and 61 kDa for the core protein. In the presence of NGF, these values were 90-190 kDa, 10 kDa, and 51 kDa and 61 kDa, respectively. The intact forms of cell-associated CSPG had apparent molecular mass ranges of 120-150 kDa and 120-190 kDa (Kav = 0.38 and 0.34), with CSs of 15 kDa and 20 kDa in the presence and absence of NGF, respectively. The apparent molecular mass of the core protein of cell-associated CSPG was 92 kDa, irrespective of the presence of NGF. The molecular sizes of cell-associated PGs and their glycosaminoglycans remained unchanged during culture. (3) CSPGs released by PC12 cells into the culture medium were separated into two peaks (I and II) by column chromatography on DEAE-cellulose. The peak II fraction prepared from the medium with NGF after 3 days of culture consisted of CSPG with Kav = 0.22 on Sephacryl S-300 [40-84 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)].(ABSTRACT TRUNCATED AT 250 WORDS)

Diversity in cellular signaling for nerve growth factor and insulin: variations on a common theme

Numerous similarities exist in the cellular signaling events observed for insulin and nerve growth factor. Because the two hormones share many functional properties, and exhibit similar effects on neurons, the possibility of common early signaling events has been explored. Many studies have focused on the important role of protein phosphorylation. Two distinct but related mechanisms are discussed that may mediate, in part, the ability of these two hormones to regulate the activities of protein kinases and phosphatases.