Epinephrine synthesis in the PC12 pheochromocytoma cell line

In-vitro Approaches to Investigate the Detrimental Effect of Light on Dopaminergic Neurons

Our recent study revealed that fluorescent lamp light can penetrate deep into the brain of mice and rats leading to the development of typical histological characteristics associated with Parkinson's disease such as the loss of dopamine neurons in the substantia nigra. Monochromatic LED lights were thus used in this work to deepen our knowledge on the effects of the major wavelength peaks of fluorescent light on mouse and human dopaminergic cells. In particular, we exposed immortalized dopaminergic MN9D neuronal cells, primary cultures of mouse mesencephalic dopaminergic cells and human dopaminergic neurons differentiated from induced pluripotent stem cells (hiPSC) to different LED light wavelengths. We found that chronic exposure to LED light reduced overall undifferentiated MN9D cell number, with the most significant effects observed at wavelengths of 485 nm and 610 nm. Moreover, LED light especially at 610 nm was able to negatively impact on the survival of mouse mesencephalic dopaminergic cells and of human dopaminergic neurons derived from hiPSC. Notably, differentiated MN9D dopaminergic cells, which closely resemble mature dopamine neuronal phenotype, acutely exposed for 3 h at 610 nm, showed a clear increase in ROS production and cytotoxicity compared to controls undifferentiated MN9D cells. These increases were even more pronounced by the co-treatment with the oxidative agent H2O2. Collectively, these findings suggest that specific wavelengths, particularly those capable of penetrating deep into the brain, could potentially pose an environmental hazard in relation to Parkinson's disease.

Cell-Effective Transition-State Analogue of Phenylethanolamine N-Methyltransferase

Phenylethanolamine N-methyltransferase (PNMT) catalyzes the S-adenosyl-l-methionine (SAM)-dependent methylation of norepinephrine to form epinephrine. Epinephrine is implicated in the regulation of blood pressure, respiration, Alzheimer's disease, and post-traumatic stress disorder (PTSD). Transition-state (TS) analogues bind their target enzymes orders of magnitude more tightly than their substrates. A synthetic strategy for first-generation TS analogues of human PNMT (hPNMT) permitted structural analysis of hPNMT and revealed potential for second-generation inhibitors [Mahmoodi, N.; J. Am. Chem. Soc. 2020, 142, 14222-14233]. A second-generation TS analogue inhibitor of PNMT was designed, synthesized, and characterized to yield a Ki value of 1.2 nM. PNMT isothermal titration calorimetry (ITC) measurements of inhibitor 4 indicated a negative cooperative binding mechanism driven by large favorable entropic contributions and smaller enthalpic contributions. Cell-based assays with HEK293T cells expressing PNMT revealed a cell permeable, intracellular PNMT inhibitor with an IC50 value of 81 nM. Structural analysis demonstrated inhibitor 4 filling catalytic site regions to recapitulate both norepinephrine and SAM interactions. Conformation of the second-generation inhibitor in the catalytic site of PNMT improves contacts relative to those from the first-generation inhibitors. Inhibitor 4 demonstrates up to 51,000-fold specificity for PNMT relative to DNA and protein methyltransferases. Inhibitor 4 also exhibits a 12,000-fold specificity for PNMT over the α2-adrenoceptor.

Effects of Curcumin on Axon Growth and Myelin Sheath Formation in an In Vitro Model

Although the beneficial effects of curcumin, extracted from rhizomes of the ginger family genus Curcuma, on the repair and regeneration of nerves have been evaluated in vitro, there are few studies concerning its effects on axon myelination. Here, we used pheochromocytoma cells as an in vitro model of peripheral nerves. Pheochromocytoma cells were cultured alone or cocultured with Schwann cells and treated with increasing concentrations of curcumin. Cell growth was observed, and the expression levels of growth-associated protein 43 (GAP-43), microtubule-associated protein 2 (MAP-2), myelin basic protein (MBP), myelin protein zero (MPZ), Krox-20, and octamer binding factor 6 (Oct-6) were quantified. We found a significant increase in expression of all six proteins following curcumin treatment, with a corresponding increase in the levels of MBP, MPZ, Krox-20, and Oct-6 mRNA. Upregulation was greater with increasing curcumin concentration, showing a concentration-dependent effect. The results suggested that curcumin can promote the growth of axons by upregulating the expression of GAP-43 and MAP-2, stimulate synthesis and secretion of myelin-related proteins, and facilitate formation of the myelin sheath in axons by upregulating the expression of Krox-20 and Oct-6. Therefore, curcumin could be widely applied in future strategies for the treatment of nerve injuries.

Inflammatory Signaling in Hypertension: Regulation of Adrenal Catecholamine Biosynthesis

The immune system is increasingly recognized for its role in the genesis and progression of hypertension. The adrenal gland is a major site that coordinates the stress response via the hypothalamic-pituitary-adrenal axis and the sympathetic-adrenal system. Catecholamines released from the adrenal medulla function in the neuro-hormonal regulation of blood pressure and have a well-established link to hypertension. The immune system has an active role in the progression of hypertension and cytokines are powerful modulators of adrenal cell function. Adrenal medullary cells integrate neural, hormonal, and immune signals. Changes in adrenal cytokines during the progression of hypertension may promote blood pressure elevation by influencing catecholamine biosynthesis. This review highlights the potential interactions of cytokine signaling networks with those of catecholamine biosynthesis within the adrenal, and discusses the role of cytokines in the coordination of blood pressure regulation and the stress response.

High-resolution imaging of cellular dopamine efflux using a fluorescent nanosensor array

Intercellular communication via chemical signaling proceeds with both spatial and temporal components, but analytical tools, such as microfabricated electrodes, have been limited to just a few probes per cell. In this work, we use a nonphotobleaching fluorescent nanosensor array based on single-walled carbon nanotubes (SWCNTs) rendered selective to dopamine to study its release from PC12 neuroprogenitor cells at a resolution exceeding 20,000 sensors per cell. This allows the spatial and temporal dynamics of dopamine release, following K⁺ stimulation, to be measured at exceedingly high resolution. We observe localized, unlabeled release sites of dopamine spanning 100 ms to seconds that correlate with protrusions but not predominately the positive curvature associated with the tips of cellular protrusions as intuitively expected. The results illustrate how directionality of chemical signaling is shaped by membrane morphology, and highlight the advantages of nanosensor arrays that can provide high spatial and temporal resolution of chemical signaling.

In vitro models for neurotoxicology research

The nervous system has a highly complex organization, including many cell types with multiple functions, with an intricate anatomy and unique structural and functional characteristics; the study of its (dys)functionality following exposure to xenobiotics, neurotoxicology, constitutes an important issue in neurosciences.

Protective effect of arachidonic acid and linoleic acid on 1-methyl-4-phenylpyridinium-induced toxicity in PC12 cells

Background

Parkinson’s disease is a neurodegenerative disorder that is being characterized by the progressive loss of dopaminergic neurons of the nigrostriatal pathway in the brain. The protective effect of omega-6 fatty acids is unclear. There are lots of contradictions in the literature with regard to the cytoprotective role of arachidonic acid. To date, there is no solid evidence that shows the protective role of omega-6 fatty acids in Parkinson’s disease. In the current study, the potential of two omega-6 fatty acids (i.e. arachidonic acid and linoleic acid) in alleviating 1-methyl-4-phenylpyridinium (MPP⁺)-induced cytotoxicity in PC12 cells was examined.

Methods

Cultured PC12 cells were either treated with MPP⁺ alone or co-treated with one of the omega-6 fatty acids for 1 day. Cell viability was then assessed by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

Results

Cells treated with 500 μM MPP⁺ for a day reduced cell viability to ~70% as compared to control group. Linoleic acid (50 and 100 μM) significantly reduced MPP⁺-induced cell death back to ~85-90% of the control value. The protective effect could be mimicked by arachidonic acid, but not by ciglitazone.

Conclusions

Both linoleic acid and arachidonic acid are able to inhibit MPP⁺-induced toxicity in PC12 cells. The protection is not mediated via peroxisome proliferator-activated receptor gamma (PPAR-γ). Overall, the results suggest the potential role of omega-6 fatty acids in the treatment of Parkinson’s disease.

Tianeptine interferes with microtubule organization and hormone secretion of pheochromocytoma cells

Pheochromocytoma originates from chromaffin cells in the adrenal medulla and sympathetic paraganglia. 36-53% of pheochromocytoma becomes malignant and, thereafter, resistant to conventional treatments. Pheochromocytoma also causes hyper-secretion of catecholamines that cause severe hypertension. We found that an antidepressant, tianeptine, interfered with normal life cycle of pheochromocytoma cells at its clinical doses. Treatment with tianeptine caused microtubule bundling and specific degradation of cytoplasmic dynein, a retrograde microtubule motor that mediates various microtubule-dependent processes during interphase and mitosis, in the rat pheochromocytoma PC12 cells. Tianeptine also increased the levels of pro-apoptotic proteins, slowed cell cycle progression, and increased apoptosis in PC12 cells. Importantly, tianeptine treatment decreased high K(+)-stimulated secretion of norepinephrine and chromogranin A in PC12 cells and of epinephrine in the mouse pheochromocytoma MPC cells. Our study demonstrates, for the first time, that tianeptine interferes with normal life cycle of pheochromocytoma cells.

Review of the history and current status of cell-transplant approaches for the management of neuropathic pain

Treatment of sensory neuropathies, whether inherited or caused by trauma, the progress of diabetes, or other disease states, are among the most difficult problems in modern clinical practice. Cell therapy to release antinociceptive agents near the injured spinal cord would be the logical next step in the development of treatment modalities. But few clinical trials, especially for chronic pain, have tested the transplant of cells or a cell line to treat human disease. The history of the research and development of useful cell-transplant-based approaches offers an understanding of the advantages and problems associated with these technologies, but as an adjuvant or replacement for current pharmacological treatments, cell therapy is a likely near future clinical tool for improved health care.

Effects of anonaine on dopamine biosynthesis and L-DOPA-induced cytotoxicity in PC12 cells

The effects of anonaine, an aporphine isoquinoline alkaloid, on dopamine biosynthesis and L-DOPA-induced cytotoxicity in PC12 cells were investigated. Anonaine at concentration ranges of 0.01-0.2 microM showed a significant inhibition of dopamine content at 24 h, with an IC(50) value of 0.05 microM. Anonaine at 0.05 microM inhibited tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) activities to 38.4-40.2% and 78.4-90.2% of control levels at 12-24 h and 3-6 h, respectively. TH activity was more influenced than AADC activity. Anonaine also decreased intracellular cyclic AMP levels, but not intracellular Ca(2+) concentrations. In addition, anonaine (0.05 microM) reduced L-DOPA (50 microM and 100 microM)-induced increases in dopamine content at 24 h. However, anonaine (0.05 microM) did not enhance L-DOPA (50 microM and 100 microM)-induced cell death after 24 h. These results suggest that anonaine inhibits dopamine biosynthesis by mainly reducing TH activity without aggravating L-DOPA-induced cytotoxicity in PC12 cells.

Liriodenine inhibits dopamine biosynthesis and L-DOPA-induced dopamine content in PC12 cells

The inhibitory effects of liriodenine, an aporphine isoquinoline alkaloid, on dopamine biosynthesis and L-DOPA-induced dopamine content increases in PC12 cells were investigated. Treatment of PC12 cells with 5-10 microM liriodenine significantly decreased the intracellular dopamine content in a concentration-dependent manner (IC50 value, 8.4 microM). Liriodenine was not cytotoxic toward PC12 cells at concentrations up to 20 microM. Tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) activities were inhibited by 10 microM liriodenine to 20-70% and 10-14% of control levels at 3-12 h, respectively; TH activity was more influenced than AADC activity. The levels of TH mRNA, intracellular cyclic AMP and basal Ca2+ concentration were also decreased by 10 microM liriodenine. In addition, 10 microM liriodenine reduced L-DOPA (20-100 microM)-induced increases in dopamine content. However, 10 microM liriodenine resulted in a protective effect against L-DOPA (50-100 microM)-induced cytotoxicity. These results suggest that liriodenine regulates dopamine biosynthesis by partially reducing TH activity and TH gene expression and has protective effects against L-DOPA-induced cytotoxicity in PC12 cells.

Alteration of hormone and neurotransmitter production in cultured cells by high and low frequency electrical stimulation

HFS has become a widely used method in functional neurosurgery. However, its mechanism is not well understood, and its cellular and molecular effects have not yet been investigated. The aim of the study was to understand which cellular events, unrelated to the network organization of cells or neurons, participate in the mechanism of action of HFS. In vitro cellular effects of high (HFS) and low (LFS) frequency electrical stimulation on prolactin secretion in GH3 cell lines (prolactinoma), as well as the catecholaminergic secretion on PC12 cells (pheochromocytoma) were investigated. Cells were cultured in dishes with integrated electrodes to deliver stimulation at the same parameters as those used in clinical conditions to treat advanced forms of Parkinson's disease. Prolactin production was measured in GH3 using a Radio-Immuno-Assay. Dopamine, epinephrine and norepinephrine were measured in PC12 using Enzymo-immuno-assays. HFS for 24 hours reduced prolactin secretion by 40.3%, dopamine by 32.7%, epinephrine by 18.1% (non significant) and norepinephrine by 27.0%. LFS did not induce significant changes. These results suggest that HFS has an inhibitory impact on the cellular machinery responsible for hormone and neurotransmitter production. In this model of isolated cultured cells, network interactions and particularly presynaptic actions are discarded. HFS has inhibitory effects on cellular mechanisms responsible for the production and release of molecules participating in intercellular communication. This HFS-induced inhibition might participate in the lesion-like effect of therapeutic HFS in the basal ganglia during various movement disorders.

Cell therapy for neuropathic pain in spinal cord injuries

Cell therapy to treat neuropathic pain after spinal cord injury (SCI) is in its infancy. However, the development of cellular strategies that would replace or be used as an adjunct to existing pharmacological treatments for neuropathic pain have progressed tremendously over the past 20 years. The earliest cell therapy studies for pain relief tested adrenal chromaffin cells from rat or bovine sources, placed in the subarachnoid space, near the spinal cord pain- processing pathways. These grafts functioned as cellular minipumps, secreting a cocktail of antinociceptive agents around the spinal cord for peripheral nerve injury, inflammatory or arthritic pain. These initial animal, and later clinical, studies suggested that the spinal intrathecal space was a safe and accessible location for the placement of cell grafts. However, one major problem was the lack of a homogeneous, expandable cell source to supply the antinociceptive agents. Cell lines that can be reversibly immortalised are the next phase for the development of a practical, homogenous cell source. These technologies have been modelled with a variety of murine cell lines, derived from embryonic adrenal medulla or CNS brainstem, in which cells are transplanted, which downregulate their proliferative, oncogenic phenotype either before or after transplant. An alternative approach for existing human cell lines is the use of neural or adrenal precursors, in which the antinociceptive properties are induced by in vitro treatment with molecules that move the cells to an irreversible neural or chromaffin, and non-oncogenic, phenotype. Although such human cell lines are at an early stage of investigation, their clinical antinociceptive potential is significant given the daunting problem of difficult-to-treat neuropathic SCI pain.

Enantio-selective inhibition of (1R,9S)- and (1S,9R)-beta-hydrastines on dopamine biosynthesis in PC12 cells

The inhibitory effects of (1R,9S)- and (1S,9R)-enantiomers of beta-hydrastine (BHS) on dopamine biosynthesis in PC12 cells were investigated. (1R,9S)-BHS decreased the intracellular dopamine content with the IC50 value of 14.3 microM at 24 h, but (1S,9R)-BHS did not. (1R,9S)-BHS was not cytotoxic at concentrations up to 250 microM towards PC12 cells. In these conditions, (1R,9S)-BHS inhibited tyrosine hydroxylase (TH) activity mainly in a concentration-dependent manner (33% inhibition at 20 microM) and decreased TH mRNA level in PC12 cells. The inhibitory patterns of dopamine content and TH activity by (1R,9S)-BHS showed similar behavioral curves. (1R,9S)-BHS at 10-50 microM also reduced the intracellular cyclic AMP level and Ca2+ concentration. In addition, treatment of L-DOPA at 20-50 microM for 24 h increased the intracellular dopamine content to 198-251% compared with the control in PC12 cells. However, the increase in dopamine levels induced by L-DOPA (20-50 microM) was reduced when L-DOPA was combined with (1R,9S)-BHS (10-50 microM). These results indicate that (1R,9S)-BHS, but not (1S,9R)-BHS, reduced dopamine content and L-DOPA-induced increase in dopamine content, in part, through the inhibition of TH activity and TH gene expression in PC12 cells: thus, (1R,9S)-BHS proved to have a function to regulate dopamine biosynthesis.

Useful cell lines derived from the adrenal medulla

Five approaches for the preparation of adrenal chromaffin cell lines have been developed. Initially, continuous chromaffin lines were derived from spontaneous pheochromocytoma tumors of the medulla, either from murine or human sources, such as the rat PC12 cell line and the human KNA and KAT45 cell lines. Over the last few decades, more sophisticated molecular methods have allowed for induced tumorigenesis and targeted oncogenesis in vivo, where isolation of specific populations of mouse cell lines of endocrine origin have resulted in model cells to examine a variety of regulatory pathways in the chromaffin phenotype. As well, conditional immortalization with retroviral infection of chromaffin precursors has provided homogeneous and expandable chromaffin cells for transplant studies in animal models of pain. This same strategy of immortalization with conditionally expressed oncogenes has been expanded recently to create the first disimmortalizable chromaffin cells, with an excisable oncogenic cassette, as might be envisioned for the creation of human chromaffin cell lines. Eventually, as we increase our understanding of regulating the phenotypic fate of chromaffin cells in vitro, stem or progenitor adrenal medullary cell lines will be derived as an alternative source for expansion and clinical use.

Combinatorial code of growth factors and neuropeptides define neuroendocrine differentiation in PC12 cells

Adrenal chromaffin cells constitute one of the first cell types to have been defined as a neuroendocrine cell type. Since they produce dopamine, these cells have been proposed for the treatment of neuronal deficits in human Parkinson's disease. However, the factors involved in the development of chromaffin cells are still poorly understood. Based on recent insights from stem cell research, we decided to study the role of extracellular matrices, growth factors and neuropeptides on the neuroendocrine differentiation in a serum-free medium of PC12 cells. Employing immunohistochemistry, quantitative PCR and HPLC analysis, neuroendocrine differentiation was determined by evaluating neurite outgrowth, catecholamine biosynthesis and release as well as neuropeptide and vesicular protein mRNA expression. The combination of bFGF, NGF and PACAP could prevent the inhibition of neurite process development induced by dexamethasone in PC12 cells cultured on ECM. Whereas glucocorticoids were essential in the regulation of enzymes of catecholamine biosynthesis and metabolism, growth factors and PACAP were more efficient in inducing neuropeptide and chromogranin B expression as well as release of dopamine and 3-methoxytyramine. Therefore, in addition to glucocorticoids, chromaffin cells need a gradient of matrix, growth factors, and neuropeptides to develop the full functional phenotype of a neuroendocrine cell.

Differential expression of the noradrenaline transporter in adrenergic chromaffin cells, ganglion cells and nerve fibres of the rat adrenal medulla

Expression of the noradrenaline transporter (NAT) was identified in various cell and fibre populations of the rat adrenal medulla, examined with immunohistochemistry and confocal microscopy. Immunoreactivity for the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), aromatic-L-amino-acid decarboxylase (AADC) and dopamine beta-hydroxylase (DBH) was present in all chromaffin cells, while phenylethanolamine N-methyltransferase (PNMT) was used to determine adrenergic chromaffin cell groups. Labelling with NAT antibody was predominantly cytoplasmic and colocalised with PNMT immunoreactivity. Noradrenergic chromaffin cells were not NAT immunoreactive. Additionally, NAT antibody labelling demonstrated clusters of ganglion cells (presumably Type I) and nerve fibres. Expression of TH, AADC, DBH, PNMT and NAT mRNA was examined using reverse transcription-polymerase chain reaction (RT-PCR) from adrenal medulla punches and single chromaffin cells, and results were consistent with those obtained with immunocytochemistry. Chromaffin cells and fibres labelled with antibodies against growth associated protein-43 (GAP-43) were not NAT immunoreactive, while ganglion cells were doubled labelled with the two antibodies. The presence of NAT in adrenergic chromaffin cells, and its absence from noradrenergic cells, suggests that the adrenergic cell type is primarily responsible for uptake of catecholamines in the adrenal medulla.

Inhibition of dopamine biosynthesis by protoberberine alkaloids in PC12 cells

Berberine and palmatine exhibit a mild and competitive inhibition on bovine adrenal tyrosine hydroxylase (EC 1.14.16.2; TH). In this study, the inhibitory effects of protoberberine alkaloids (such as berberine, palmatine and coptisine) on dopamine biosynthesis in PC12 cells were investigated. Treatment with berberine and palmatine showed 53.7% and 61.0% inhibition of dopamine content in PC12 cells at a concentration of 20 microM for 24 hr, respectively. However, coptisine did not reduce dopamine content. The IC50 values of berberine and palmatine were 18.6 microM and 7.9 microM. Dopamine content was lowered at 6 hr and reached the minimal level at 24 hr after exposure to berberine and palmatine at 20 microM. The decreased dopamine level was maintained up to 48 hr, and then recovered to the control level at about 72 hr. TH activity was inhibited at 6 hr following treatment with berberine and palmatine, and was maintained at a reduced level up to 36 hr in PC12 cells (21-27% inhibition at 20 microM), whereas TH mRNA level was not found to alter for 24 hr. However, the intracellular Ca2+ concentration decreased by treatment with berberine and palmatine at 20 microM by 22-26% inhibition relative to the control level in PC12 cells. These results give evidence that berberine and palmatine lead to decreased dopamine content by inhibition of TH activity but not by regulation of TH gene expression in PC12 cells.

Simulated microgravity conditions enhance differentiation of cultured PC12 cells towards the neuroendocrine phenotype

We are studying microenvironmental cues which contribute to neuroendocrine organ assembly and tissue-specific differentiation. As our in vitro model, we cultured rat adrenal medullary PC12 pheochromocytoma cells in a novel cell culture system, the NASA rotating wall vessel (RWV) bioreactors. This "simulated microgravity" environment in RWV bioreactors, characterized by randomizing gravitational vectors and minimizing shear stress, has been shown to favor macroscopic tissue assembly and to induce tissue-specific differentiation. We hypothesized that the unique culture conditions in the RWV bioreactors might enhance the in vitro formation of neuroendocrine organoids. To test our hypothesis, we evaluated the expression of several markers of neuroendocrine differentiation in cultures of PC12 cells maintained for up to 20 d in the slow turning lateral vessel (STLV) type RWV. PC12 cell differentiation was assessed by morphological, immunological, biochemical and molecular techniques. PC12 cells, cultured under "simulated microgravity" conditions, formed macroscopic, tissue-like organoids several millimeters in diameter. Concomitantly, the expression of phenylethanolamine-N-methyl transferase (PNMT), but not of other catecholamine synthesizing enzymes, was enhanced. Increased PNMT expression, as verified on both the gene and protein level, was accompanied by an increase in the specific activity of the enzyme. Furthermore, after 20 d in culture in the STLV, we observed altered patterns of protein tyrosine phosphorylation and prolonged activation of c-fos, a member of the AP-1 nuclear transcription factor complex. We conclude that culture conditions in the RWV appear to selectively activate signal transduction pathways leading to enhanced neuroendocrine differentiation of PC12 cells.

Inhibitory effects of bulbocapnine on dopamine biosynthesis in PC12 cells

The effects of bulbocapnine, an aporphine isoquinoline alkaloid, on dopamine biosynthesis in PC12 cells were investigated. Bulbocapnine showed 45.2% inhibition on dopamine content in PC12 cells at a concentration of 20 microM for 12 h. The IC50 value of bulbocapnine was 26.7 microM. Bulbocapnine at concentrations up to 80 microM was not cytotoxic towards PC12 cells. Tyrosine hydroxylase (TH) activity was inhibited by the treatment of bulbocapnine in PC12 cells (24.4% inhibition at 20 microM). Bulbocapnine at 20 microM also decreased the intracellular Ca2+ concentration by 12.9% inhibition relative to control in PC12 cells. However, TH mRNA level was not altered by bulbocapnine treatment. These results suggest that the inhibition of TH activity by bulbocapnine might be involved in at least one component of the reduction of dopamine biosynthesis in PC12 cells.

Staurosporine induces neurite outgrowth in neuronal hybrids (PC12EN) lacking NGF receptors

A novel neuronal model (PC12EN cells), obtained by somatic hybridization of rat adrenal medullary pheochromocytoma (PC12) and bovine adrenal medullary endothelial (BAME) cells, was developed. PC12EN cells maintained numerous neuronal characteristics: they expressed neuronal glycolipid conjugates, synthesized and secreted catecholamines, and responded to differentiative agents with neurite outgrowth. PC12EN lacked receptors for EGF and both the p75 and trk NGF receptors, while FGF receptor expression was maintained. Staurosporine (5-50 nM), but not other members of the K252a family of protein kinase inhibitors, rapidly induced neurite outgrowth in PC12EN, as also found in the parental PC12 cells, but not in BAME cells. Similarly, both acidic and basic FGF (1-100 ng/ml) were neurotropic in PC12EN. In contrast to the mechanism by which FGF promoted neurite outgrowth in PC12EN, the neurotropic effect of staurosporine did not involve activation of established signalling pathways, such as tyrosine phosphorylation of erk (ras pathway) or SNT (a specific target of neuronal differentiation). In addition, staurosporine induced the tyrosine phosphorylation of the focal adhesion kinase p125FAK. However, since the latter effect was also observed with other protein kinase inhibitors of the K252a family, which induced PC12EN cells flattening but no neurite extension, we propose that FAK tyrosine phosphorylation may be related to ubiquitous changes in cell shape. We anticipate that PC12EN neuronal hybrids will become useful models in neuroscience research for evaluating unique cellular signalling mechanisms of novel neurotropic compounds.

Two PC12 pheochromocytoma lines sealed in hollow fiber-based capsules tonically release L-dopa in vitro

Two PC12 cell-derived lines have been studied following encapsulation into polymer-based hollow fibers with respect to secreted catecholamines and their metabolites. Cellular encapsulation provides a chronic microperfusion environment within which basally secreted PC12 products can be readily measured. Encapsulated PC12 cells grown and held under the conditions specified in this report basally release amounts exceeding their total cellular stores of the dopamine precursor L-DOPA and the electrochemically active dopamine metabolites DOPAC and HVA during 45-min static incubations. Under these same conditions, these cells release less than 0.1% of their total cellular store of dopamine. Depolarizing incubations enhance dopamine secretion eightyfold and enhance secretion of L-DOPA, HVA, and DOPAC about twofold. The relative composition of products basally secreted differs between PC12-derived cell lines, and an inverse relationship exists between basal release of L-DOPA and total cellular store of dopamine. These results further indicate that selected PC12 cell lines are potentially a source of both dopamine and L-DOPA in therapeutic cellular replacement applications.

Parallel up-regulation of catecholamine biosynthetic enzymes by dexamethasone in PC12 cells

We sought to investigate whether dexamethasone produces a coordinated, time-dependent effect on all enzymes in the catecholamine biosynthetic pathway in PC12 cells. The levels of mRNAs of tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), and dopamine beta-hydroxylase (DBH) were examined at 0, 6, 12, 24, and 48 h after dexamethasone (5 microM) treatment to PC12 cells. The levels of all enzyme mRNAs steadily increased for 24 h, although the increase of AADC mRNA content was slow. The increased mRNA levels of TH and AADC were maintained at 48 h, whereas the level of DBH mRNA was sharply decreased at 48 h. The maximally induced mRNA levels were approximately 5.0-, 2.4-, and 7.0-fold higher than the control levels of TH, AADC, and DBH, respectively. The elevation of enzyme activities was detected later than the increase in levels of mRNAs. The maximal activities of TH, AADC, and DBH were reached between 48 and 72 h with 3.6-, 1.8-, and 8.0-fold increases, respectively. Low, but detectable, phenylethanolamine N-methyltransferase (PNMT) activity was observed in PC12 cells, and dexamethasone increased its activity 5.6-fold at 72 h. The PNMT mRNA was easily detected by northern blot analysis after exposure for 24 h to dexamethasone. The data suggest that, in PC12 cells, dexamethasone up-regulates all catecholamine biosynthetic enzyme genes in a parallel fashion.

Differentiation of PC12 cells with v-src: comparison with nerve growth factor

The PC12 rat pheochromocytoma cell line is used extensively as a model to study neuronal differentiation. These cells resemble adrenal chromaffin cells, differentiating both morphologically and biochemically when cultured in the presence of dexamethasone, but develop a sympathetic neuron-like phenotype when cultured in the presence of nerve growth factor. Expression of the protein product of the v-src oncogene in PC12 cells also induces neurite outgrowth similar to that resulting from nerve growth factor treatment (Alema et al: Nature 316:557-559, 1985). It is thus possible that c-src or a src-like tyrosine kinase participates in the signal transduction pathway by which nerve growth factor acts on PC12 cells. In this study a temperature-sensitive v-src gene has been introduced into PC12 cells. When cultures of these src-transformed cells are switched from the nonpermissive (40 degrees C) to the permissive (37 degrees C) temperature they elaborate neurites. The differentiation induced by src has been compared with that induced by nerve growth factor by determining whether src-transformed PC12 cells at 37 degrees C exhibit the same biochemical alterations as those induced in PC12 cells treated with nerve growth factor. Neurite extension at 37 degrees C in v-src-transformed cells, like NGF-induced differentiation, is accompanied by an increase in the nerve growth factor-inducible large external (NILE) protein. However, neurite extension in v-src-transformed cells is not blocked by the protein kinase inhibitor K-252a, which completely blocks NGF-induced neurite extension. Likewise, EGF receptor down-regulation and the development of saxitoxin and tetanus toxin binding sites are either much reduced or completely absent in src-differentiated compared with NGF-differentiated PC12 cells.

Decreased levels of nerve growth factor receptor on dexamethasone-treated PC12 cells

Treatment of PC12 cells with dexamethasone leads, in a period of days, to a 60% decrease in the binding of (125I)nerve growth factor. The decrease was maximal after 3 days of treatment with 1 microM dexamethasone, but some decrease was seen after 6 hr and at concentrations as low as 10 nM. The effect was specific for the glucocorticosteroids. Scatchard plots confirmed the overall loss of nerve growth factor binding, and studies with trypsin digestion and Triton X-100 extraction indicated that the decrease in binding was largely due to a decrease in the number of low-affinity receptors. Nerve growth factor-induced changes, such as the induction of ornithine decarboxylase and the generation of neurites, were inhibited, but only minimally, in dexamethasone-treated cells.