Molecular mechanism of nur77 gene expression and downstream target genes in the early stage of forskolin-induced differentiation in PC12 cells

3-Amino-5,6,7,8-tetrahydrothieno[2,3-b]quinoline-2-carbonitrile: A fluorescent molecule that induces differentiation in PC12 cells

Neural differentiation is triggered by the activation of multiple signaling pathways initiated by various neurotrophic factors. An elucidation of these mechanisms is anticipated to facilitate the prevention of diseases and the development of novel therapeutic approaches. Alternative small-molecule inducers for neuroscience studies are required instead of protein-based reagents for more efficient and convenient experiments. We demonstrated that small molecules of thieno[2,3-b]pyridine derivatives that induce neural differentiation, compounds 3a and 9a in particular, exhibited significant neuritogenic activity in rat pheochromocytoma (PC12) cells. Moreover, 3a displayed pronounced fluorescence and a discernible Stokes shift. Furthermore, the outcome of the experiment conducted on the NGF-insensitive clones of rat PC12 cells, and the results of the intercellular uptake analyses suggested that the 3a-mediated activation of neural differentiation occurred independently of the TrkA receptor. Therefore, 3a portrays potential applicability both as a small molecule reagent to replace novel neurotrophic factors and as a potent fluorescent reagent for various techniques, including bioimaging.

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

The Heterogeneity of Response of PC12 Cells from Different Laboratories to Nerve Growth Factor and Pituitary Adenylate Cyclase-Activating Polypeptide Questions the Reproducibility of Studies Carried Out with Tumor Cell Lines

BACKGROUND

PC12 pheochromocytoma tumor cell lines are widely used to decipher the intracellular signaling mechanisms mediating the effects of some growth factors. Nevertheless, the disparity in appearance of some PC12 cell lines used in the different publications questions our ability to compare the results obtained by the numerous laboratories which use them. This led us to analyze the phenotypic aspect and transcriptomic expression of 5 PC12 cell lines from different origins under control conditions and after treatment with nerve growth factor (NGF) or pituitary adenylate cyclase-activating polypeptide (PACAP).

METHODS

Characterization of the 5 PC12 cell lines was conducted using imaging techniques and high-throughput real-time PCR combined with bioinformatics analysis.

RESULTS

The results show that the 5 cell lines are very variable in terms of shape, proliferation rate, motility, adhesion to the substrate, and gene expression. This high heterogeneity of the cell lines is also found when looking at their response to NGF or PACAP on gene expression or differentiation, with even in some cases opposite effects, as, for example, on cell proliferation. Actually, only 2 of the cell lines tested exhibited some phenotypic similarities with each other, even though the transcriptomic analyses show that they are far from identical.

DISCUSSION/CONCLUSION

As this issue of cell heterogenicity is not restricted to PC12 cells, the present results highlight the need to facilitate the supply of cell lines at low cost, the necessity to standardize practices regarding the use of cell lines, and the requirement to define precise markers of established cell lines which should be monitored in every publication. Regarding this latter point, the present data show that transcriptomic analysis by real-time PCR using a panel of genes of interest is easy to implement and provides a reliable method to control the possible drift of the cells over time in culture. Transcriptomic phenotyping combined with bioinformatics analysis can also be a useful approach to predict the response of the cells to treatments in terms of cell signaling activation, which can help to choose among several cell lines the most appropriate one for the investigation of a particular mechanism. Taken together, the results from this study highlight the need to use well-characterized cell lines with standardized protocols to generate reproducible results from 1 laboratory to the other.

Muscle Stem Cell Function Is Impaired in β2-Adrenoceptor Knockout Mice

Knockout (ko) mice for the β2 adrenoceptor (Adrβ2) have impaired skeletal muscle regeneration, suggesting that this receptor is important for muscle stem cell (satellite cell) function. Here, we investigated the role of Adrβ2 in the function of satellite cells from β2ko mice in the context of muscle regeneration, through in vivo and in vitro experiments. Immunohistochemical analysis showed a significant reduction in the number of self-renewed Pax7⁺ satellite cells, proliferating Pax7⁺/MyoD⁺ myogenic precursor cells, and regenerating eMHC⁺ myofibers in regenerating muscle of β2ko mice at 30, 3, and 10 days post-injury, respectively. Quiescent satellite cells were isolated by fluorescence-activated cell sorting, and cell cycle entry was assessed by EdU incorporation. The results demonstrated a lower number of proliferating Pax7⁺/EdU⁺ satellite cells from β2ko mice. There was an increase in the gene expression of the cell cycle inhibitor Cdkn1a and Notch pathway components and the activation of Notch signaling in proliferating myoblasts from β2ko mice. There was a decrease in the number of myogenin-positive nuclei in myofibers maintained in differentiation media, and a lower fusion index in differentiating myoblasts from β2ko mice. Furthermore, the gene expression of Wnt/β-catenin signaling components, the expression of nuclear β-catenin and the activation of Wnt/β-catenin signaling decreased in differentiating myoblasts from β2ko mice. These results indicate that Adrβ2 plays a crucial role in satellite cell self-renewal, as well as in myoblast proliferation and differentiation by regulating Notch and Wnt/β-catenin signaling, respectively.

FOXA3, a Negative Regulator of Nur77 Expression and Activity in Testicular Steroidogenesis

Biosynthesis of testosterone occurs mainly in the testicular Leydig cells. Nur77, an orphan nuclear receptor that is expressed in response to the luteinizing hormone/cyclic adenosine monophosphate (LH/cAMP) signaling pathway, is one of the key factors that regulate steroidogenesis in Leydig cells. The function of Nur77 is modulated through interaction with other proteins. FOXA3, a transcription factor that is crucial for male fertility, is also expressed in Leydig cells. Here, we sought to elucidate the role of FOXA3 in testicular steroidogenesis by focusing on its interaction with Nur77. LH/cAMP signaling induces the onset of steroidogenesis in Leydig cells but has a repressive effect on the expression of FOXA3. Overexpression of FOXA3 in MA-10 Leydig cells repressed cAMP-induced expression of Nur77 and its target steroidogenic genes (StAR, P450c17, and Hsd3β). Furthermore, FOXA3 suppressed Nur77 transactivation of the promoter of steroidogenic genes. In mouse primary Leydig cells, adenovirus-mediated overexpression of FOXA3 had similar effects and resulted in decreased production of testosterone. Taken together, these results suggest the role of FOXA3 in the regulation of steroidogenic genes in Leydig cells and fine-tuning steroidogenesis in the testis.