The extracellular matrix modulates the response of PC12 cells to nerve growth factor: cell aggregation versus neurite outgrowth on 3-dimensional laminin substrata

Multimodal treatment combining cold atmospheric plasma and acidic fibroblast growth factor for multi-tissue regeneration

Cold atmospheric plasma (CAP) is an emerging technology for biomedical applications, exemplified by its antimicrobial and antineoplastic potentials. On the contrary, acidic fibroblast growth factor (aFGF) has been a long-standing potent mitogen for cells from various origins. In this study, we are the first to develop a multimodal treatment combining the aforementioned physicochemical and pharmacological treatments and investigated their individual and combined effects on wound healing, angiogenesis, neurogenesis, and osteogenesis. This work was performed at the tissue, cellular, protein, and gene levels, using histochemical staining, flow cytometry, ELISA, and PCR, respectively. Depending on the type of target tissue, various combinations of aforementioned methods were used. The results showed that the enhancement on would healing and angiogenesis by CAP and aFGF were synergistic. The former was manifested by increased murine fibroblast proliferation and reduced cutaneous tissue inflammation, whereas the latter by upregulated proangiogenic markers in vivo, for example, CD31, VEGF, and TGF-β, and downregulated antiangiogenic proteins in vitro, for example, angiostatin and angiopoietin-2, respectively. In addition, aFGF outperformed CAP during neurogenesis, which was evidenced by superior neurite outgrowth, while CAP exceeded aFGF in osteogenesis which was demonstrated by more substantial bone nodule formation. These novel findings not only support the fact that CAP and aFGF are both multipotent agents during tissue regeneration, but also highlight the potential of our multimodal treatment combining the individual advantages of CAP and aFGF. The versatile administration route, that is, topical and/or systemic, might further broaden its applications.

PC12 Cell Line: Cell Types, Coating of Culture Vessels, Differentiation and Other Culture Conditions

The PC12 cell line is one of the most commonly used in neuroscience research, including studies on neurotoxicity, neuroprotection, neurosecretion, neuroinflammation, and synaptogenesis. Two types of this line are available in the ATCC collection: traditional PC12 cells grown in suspension and well-attached adherent phenotype. PC12 cells grown in suspension tend to aggregate and adhere poorly to non-coated surfaces. Therefore, it is necessary to modify the surface of culture vessels. This paper aims to characterise the use of two distinct variants of PC12 cells as well as describe their differentiation and neuronal outgrowth with diverse NGF concentrations (rat or human origin) on various surfaces. In our study, we evaluated cell morphology, neurite length, density and outgrowth (measured spectrofluorimetrically), and expression of neuronal biomarkers (doublecortin and NeuN). We found that the collagen coating was the most versatile method of surface modification for both cell lines. For adherent cells, the coating was definitely less important, and the poly-d-lysine surface was as good as collagen. We also demonstrated that the concentration of NGF is of great importance for the degree of differentiation of cells. For suspension cells, we achieved the best neuronal characteristics (length and density of neurites) after 14 days of incubation with 100 ng/mL NGF (change every 48 h), while for adherent cells after 3-5 days, after which they began to proliferate. In the PC12 cell line, doublecortin (DCX) expression in the cytoplasm and NeuN in the cell nucleus were found. In turn, in the PC12 Adh line, DCX was not expressed, and NeuN expression was located in the entire cell (both in the nucleus and cytoplasm). Only the traditional PC12 line grown in suspension after differentiation with NGF should be used for neurobiological studies, especially until the role of the NeuN protein, whose expression has also been noted in the cytoplasm of adherent cells, is well understood.

Topography and coating of platinum improve the electrochemical properties and neuronal guidance

To improve neuronal-electrode interfaces, we analyzed the influence of surface topographies combined with coating on the electrochemistry of platinum and neuronal differentiation of PC-12 cells. Surface structuring on nanoscale was realized by femtosecond laser ablation. Additional coating with laminin (LA), collagen type I (COL) or poly-d-lysine (PDL) did not change the produced topography. We further demonstrated that impedance could be improved in all cases. The pre-requisites of differentiation - viability and attachment - were fulfilled on the topography. Cell attachment of non-differentiated and differentiated cells and their formation of focal adhesion complexes were even enhanced compared to unstructured platinum. However, without the nerve growth factor (NGF) no cellular outgrowth and differentiation were possible. The topography enabled cell elongation and reduced the amount of rounded cells, but less effective than coating. Differentiation was either comparable or increased on the structures when compared with unstructured coatings. For instance, microtubule associated protein (MAP2) was detected most on the topography alone. But a combination of surface structuring and coating had the strongest impact on differentiation: the usage of COL provoked best cell elongation and beta III tubulin expression, PDL best synaptophysin. LA-coating had no noteworthy effect. These findings point out that innovative electronic devices like cochlear implants include two aspects: (a) nanotopography to improve the transmission of electrical signals and neuronal attachment; and (b) an additional coating to stimulate neuronal differentiation.

Adhesion molecules promote chronic neural interfaces following neurotrophin withdrawal

Neural prostheses and recording devices have been successfully interfaced with the nervous system; however, substantial integration issues exist at the biomaterial-tissue interface. In particular, the loss of neurons at the implantation site and the formation of a gliotic scar capsule diminish device performance. We have investigated the potential of a tissue-engineered coating, consisting of adhesion molecule-modified surfaces (i.e., polylysine and collagen) in combination with neurotrophin application (i.e., brain derived neurotrophic factor, BDNF), to enhance the electrode-host interface. Neurite length and density were examined in a retinal explant model. In the presence of BDNF for 7 days, we found no synergistic effect of BDNF and adhesion molecule-modified surfaces on neurite length, although there was a possible increase in neurite density for collagen-coated surfaces. After BDNF withdrawal (7 days BDNF+/7 days BDNF- medium), we found that both polylysine and collagen treated surfaces displayed increases in neurite length and density over negative, untreated control surfaces. These results suggest that adhesion molecules may be used to support chronic neuron-electrode interfaces induced by neurotrophin exposure.

Low infra red laser light irradiation on cultured neural cells: effects on mitochondria and cell viability after oxidative stress

Background

Considerable interest has been aroused in recent years by the well-known notion that biological systems are sensitive to visible light. With clinical applications of visible radiation in the far-red to near-infrared region of the spectrum in mind, we explored the effect of coherent red light irradiation with extremely low energy transfer on a neural cell line derived from rat pheochromocytoma. We focused on the effect of pulsed light laser irradiation vis-à-vis two distinct biological effects: neurite elongation under NGF stimulus on laminin-collagen substrate and cell viability during oxidative stress.

Methods

We used a 670 nm laser, with extremely low peak power output (3 mW/cm²) and at an extremely low dose (0.45 mJ/cm²). Neurite elongation was measured over three days in culture. The effect of coherent red light irradiation on cell reaction to oxidative stress was evaluated through live-recording of mitochondria membrane potential (MMP) using JC1 vital dye and laser-confocal microscopy, in the absence (photo bleaching) and in the presence (oxidative stress) of H₂O₂, and by means of the MTT cell viability assay.

Results

We found that laser irradiation stimulates NGF-induced neurite elongation on a laminin-collagen coated substrate and protects PC12 cells against oxidative stress.

Conclusion

These data suggest that red light radiation protects the viability of cell culture in case of oxidative stress, as indicated by MMP measurement and MTT assay. It also stimulates neurite outgrowth, and this effect could also have positive implications for axonal protection.

The effect of poloxamer-188 on neuronal cell recovery from mechanical injury

Neuronal injury resulting from mechanical deformation is poorly characterized at the cellular level. The immediate structural consequences of the mechanical loading lead to a variety of inter- and intra-cellular signaling events that interact on multiple time and length scales. Thus, it is often difficult to establish cause-and-effect relationships such that appropriate treatment strategies can be devised. In this report, we showed that treating mechanically injured neuronal cells with an agent that promotes the resealing of disrupted plasma membranes rescues them from death at 24 h post-injury. A new in vitro model was developed to allow uniform mechanical loading conditions with precisely controlled magnitude and onset rate of loading. Injury severity increased monotonically with increasing peak shear stress and was strongly dependent on the rate of loading as assessed with the MTT cell viability assay, 24 h post-injury. Mechanical injury produced an immediate disruption of membrane integrity as indicated by a rapid and transient release of LDH. For the most severe injury, cell viability decreased approximately 40% with mechanical trauma compared to sham controls. Treatment of cells with Poloxamer 188 at 15 min post-injury restored long-term viability to control values. These data establish membrane integrity as a novel therapeutic target in the treatment of neuronal injury.

Endogenous somatostatin receptors mobilize calcium from inositol 1,4,5-trisphosphate-sensitive stores in NG108-15 cells

Somatostatin receptors are members of the G-protein-coupled receptor superfamily and exert their principal effects by coupling to inhibitory G-proteins. We used fura-2-based digital calcium imaging and assayed for [3H]inositol phosphates (IPs) to study the effects of somatostatin on intracellular calcium signaling in neuroblastomaxglioma NG108-15 cells. Both somatostatin-14 and octreotide induced concentration-dependent increases in intracellular Ca(2+) concentration ([Ca(2+)](i)). Thirty-four percent of the cells responded to treatment with 100 nM somatostatin-14. Somatostatin-induced responses were not blocked by the removal of extracellular calcium; instead, they were abolished by pretreatment with 100 nM thapsigargin, an agent that depletes and prevents refilling of intracellular Ca(2+) stores. Pretreatment with the inositol 1,4,5-trisphosphate (IP(3)) receptor antagonist xestospongin C (10 microM) for 20 min inhibited markedly the somatostatin-induced response. Somatostatin (100 nM) increased [3H]IPs formation. U73122 (1 microM), an inhibitor of phospholipase C (PLC), completely blocked the somatostatin-induced [Ca(2+)](i) increases and the formation of [3H]IPs. Pretreatment with pertussis toxin (PTX, 200 ng/ml) for 24 h blocked the somatostatin-induced responses. Thus, we conclude that activation of endogenous somatostatin receptors in NG108-15 cells induces the release of calcium from IP(3)-sensitive intracellular stores through PTX-sensitive G-protein-coupled PLC.

Expression and localization of utrophin in differentiating PC12 cells

To ascertain the role of utrophin in cultured neuronal cells, we investigated its expression and distribution along the NGF-induced differentiation of PC12 cells grown on different substrata. Utrophin mRNA was measured by RT-PCR assay and utrophin protein was quantified by immunoblot analysis. The distribution of utrophin and beta-dystroglycan was analyzed by confocal microscopy. We demonstrate that utrophin protein was increased 4-fold during differentiation of cells grown laminin. Concomitant with this up-regulation, utrophin was enriched at the growth cones in differentiating cells, where it co-localizes with beta-dystroglycan. These data suggest the presence of a utrophin-beta-dystroglycan complex in PC12 cells that participates in the formation and/or stabilization of the growth cone-extracellular matrix adhesion.

Neuronal laminins and their cellular receptors

The laminins are a family of extracellular matrix glycoproteins expressed throughout developing neural tissues. The laminins are potent stimulators of neurite outgrowth in vitro for a variety of cell types, presumably reflecting an in vivo role in stimulating axon outgrowth. In recent years, the laminins have been shown to occur in several distinct isoforms; currently, the precise functional differences between the laminin variants are not well understood. A variety of neuronal surface receptors have been identified for one laminin isoform, laminin-1. These receptors include several members of the integrin family, as well as non-integrin laminin-binding proteins such as LBP-110, the 67 kDa laminin-receptor, alpha-dystroglycan, and beta 1,4 galactosyltransferase. Little is currently known about receptors for other laminin isoforms.

PC12 cell aggregation and neurite growth in gels of collagen, laminin and fibronectin

PC12 cells form aggregates when suspended within three-dimensional, self-assembled, type I collagen gels; these aggregates increase in size over time. In addition, when the cells are cultured in the presence of nerve growth factor, they express neurites, which extend through the three-dimensional matrix. In this report, the roles of fibronectin, laminin and nerve growth factor in PC12 cell aggregation and neurite growth following suspension in collagen matrices were evaluated. Single cells and small clusters of cells were suspended in collagen gels; the kinetics of aggregation were determined by measurement of the projected area of each aggregate, and neurite lengths were determined by measurement of end-to-end distance. Fibronectin and laminin inhibited the aggregation of PC12 cells at 50 micrograms/ml, and fibronectin, but not laminin, inhibited the growth of neurites at 100 micrograms/ml. In the absence of serum, the aggregation of cells cultured with nerve growth factor was almost completely inhibited, but the average neurite length was unaffected. In the presence of nerve growth factor, the extent of cell aggregation could not be explained simply by an increase in cell number, suggesting the presence of two separate mechanisms for aggregate growth: one dependent on cell motility and another dependent on cell proliferation.

Proteoglycans and the modulation of cell adhesion by steric exclusion

The hypothesis that cell aggregation may be driven by linear polymers in the matrix, particularly glycosaminoglycans, is revisited in light of more recent evidence. A model is proposed that extends the concept of steric exclusion to include a role in determining the directionality of cell migration and neurite extension. Recent literature is reviewed to support the conclusion that in living tissues the theoretical conditions for driving aggregation and migration by steric exclusion are met. The ability of a linear polymer to exclude cells is a function of its viscosity, which is optimum with glycosaminoglycans similar to chondroitin sulfate. It is ineffective with low viscosity glycosaminoglycans such as most heparin or heparan sulfate. Hyaluronic acid, a massive polymer, excludes cells poorly when present as an open matrix gel but forms an effective exclusion barrier when attached to the cell surface. According to a model for steric exclusion in organogenesis, when cells have a glycocalyx of linear polymer, they should disperse and migrate down a viscosity gradient of excluding matrix polymer; when they shed or internalize their surface coat in the continued presence of matrix, they should be excluded into a smaller volume and thus stimulated to aggregate.

Nerve growth factor receptor expression in the young and adult rat olfactory system

Nerve growth factor (NGF) and its receptor (NGFR) are proteins that have a role in the normal development and survival of neurons in the peripheral and central nervous systems. During development, NGF is necessary for outgrowth of axons and establishment of synapses, and NGFR is the transmembrane protein that binds NGF and brings it into the cell. NGF and NGFR expression in the rat olfactory system have been studied previously, and age differences in NGFR are explored further in this study, using immunocytochemistry and immunoelectron microscopy to determine the changes in two different ages: postnatal day 5 and the adult. Dramatic differences were found in the distribution of NGFR immunoreactivity in the olfactory system of each of the two ages studied. Electron microscopy revealed that glial cells were responsible for this immunoreactivity.

Quantitation of the growth-associated protein B-50/GAP-43 and neurite outgrowth in PC12 cells

A combined assay to measure neurite outgrowth and B-50/GAP-43 levels in PC12 cells is reported. During NGF-induced neuritogenesis, B-50/GAP-43 expression was monitored by enzyme-linked immunosorbent assay (ELISA). Neurite outgrowth was quantified at the same time by the use of video image analysis. Sensitivity and reliability of the methods are shown with a dose-response and time curve of beta-NGF-induced neuritogenesis. A linear increase in total length of neurites was induced by concentrations of beta-NGF greater than or equal to 5 ng/ml and was accompanied by a linear increase in the amount of B-50/GAP-43. The combined methods presented here can conveniently and reliably establish subtle changes in neurite outgrowth and intracellular protein contents.

Nerve growth factor (NGF) induces neuronal differentiation in neuroblastoma cells transfected with the NGF receptor cDNA

Human nerve growth factor (NGF) receptor (NGFR) cDNA was transfected into a neuroblastoma cell line (HTLA 230) which does not express a functional NGF-NGFR signal transduction cascade. Short-term treatment of stably transfected cells (98-3) expressing membrane-bound NGF receptor molecules resulted in a cell cycle-dependent, transient expression of the c-fos gene upon treatment with NGF, suggesting the presence of functional high-affinity NGFR. Extensive outgrowth of neurites and cessation of DNA synthesis occurred in transfectants grown on an extracellular matrix after long-term treatment with NGF, suggesting terminal differentiation. Our data support the idea that introduction of a constitutively expressed NGFR cDNA into cells with neuronal background results in the assembly of a functional NGF-NGFR signal cascade in a permissive extracellular environment.

Nerve growth factor (NGF) induces neuronal differentiation in neuroblastoma cells transfected with the NGF receptor cDNA

Human nerve growth factor (NGF) receptor (NGFR) cDNA was transfected into a neuroblastoma cell line (HTLA 230) which does not express a functional NGF-NGFR signal transduction cascade. Short-term treatment of stably transfected cells (98-3) expressing membrane-bound NGF receptor molecules resulted in a cell cycle-dependent, transient expression of the c-fos gene upon treatment with NGF, suggesting the presence of functional high-affinity NGFR. Extensive outgrowth of neurites and cessation of DNA synthesis occurred in transfectants grown on an extracellular matrix after long-term treatment with NGF, suggesting terminal differentiation. Our data support the idea that introduction of a constitutively expressed NGFR cDNA into cells with neuronal background results in the assembly of a functional NGF-NGFR signal cascade in a permissive extracellular environment.