This decrease in smn protein was associated with

Info icon This preview shows pages 7–9. Sign up to view the full content.

View Full Document Right Arrow Icon
This decrease in smn protein was associated with decreased cell viability (assessed by a mitochon- drial test), increased caspase-3 activity, and elevat- ed apoptotic cell death. The increase in caspase-3 activity failed to reach significance at 48 h howev- er, the difference was much more striking by 72 h, a pattern that was reflected in the other measures. This suggests that smn depletion leads to an apop- totic process in neuronal cells, by involving the caspase-dependent pathway. These observations are consistent with histological descriptions of spinal cord pathology concerning the nature of anterior horn cell death in SMA (Hayashi et al. , 1998; Fidzianska and Rafalowska 2002). Furthermore, apoptotic cell death was observed in transgenic mouse models of SMA (Monani et al. , 2000b) and smn depleted S2 cells, which was rescued by a cas- pase inhibitor (Z-VAD-fmk) (Ilangovan et al. , 2003). In fibroblast cultures from SMA patients, caspase-3 activation was evoked by the apoptotic agent, camptothecin, or smn depletion (Wang et al. , 2005). The mechanisms by which smn may be responsible for regulating apoptosis, are likely related to its reported interactions with the Bcl2 family, p53 and ZFP1 (Fischer et al. , 1997; Young et al. , 2002; Gubitz et al. , 2004; Gangwani et al. ,
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
G.C. PARKER et al. 46 2005). However, based on the knowledge of protein-protein interactions, intracellular local- ization and transgenic animal models of smn, it is speculated that smn participates in diverse bio- logical processes such as RNA metabolism, RNA transport, axonal growth as well as apoptotic cell death (Fischer et al. , 1997; Hayashi et al. , 1998; Kerr et al. , 2000; Fan and Simard 2002; Gubitz et al. , 2004; Gangwani et al. , 2005; Doran et al. , 2006). Some of these functions may have cell autonomous components in neuronal cells (McWhorter et al. , 2003). A possible protective effect of smn in neural cells was investigated by its overproduction using adenoviral gene transfer. An increase in smn level by itself did not provide a survival advantage in native NSC-34 cells as evidenced by no increase in cell viability compared to con- trol AdV treated cells. However, increased cas- pase-3 activity, decreased cell viability and DNA fragmentation, caused by 500 nM staurosporine, were significantly mitigated by overexpression of smn protein. These experiments suggest an increase in smn regulation can ameliorate stau- rosporine induced toxicity and apoptosis in neu- ronal cells. Unpublished related data show that similar levels of SMN overexpression failed to protect cells from glutamate or nitrite oxide induced toxicity (data not shown). The non- selective protein kinase inhibitor staurosporine is commonly used to induce apoptosis (Koh et al. , 1995). In neurons, it is observed to signifi- cantly elevate caspase-3 activity within 6 h with further elevation observed at 24 h (Mercer et al. , 2000). Exposure to 1 µ M staurosporine induced apoptosis in PC12 cells associated with changes in intramitochondrial calcium level, both of which were blocked by Bcl-2 overexpression (Kruman and Mattson, 1999). In the same report, however, overexpression of the anti-apoptotic
Image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern