Date of Graduation

2018

Document Type

Thesis

Degree Type

MS

College

School of Medicine

Department

Physiology, Pharmacology & Neuroscience

Committee Chair

Emidio E Pistilli

Committee Co-Chair

Stephen E Alway

Committee Member

Junaith S Mohamed

Committee Member

Elena N Pugacheva

Abstract

Cancer-induced cachexia is a severe condition resulting in muscle wasting, muscle dysfunction, and an overall increased morbidity and mortality. The cachectic condition is often attributed to altered metabolism, aberrant activation of signaling pathways, and changes in the microenvironment of the skeletal muscle (SKM) through exposure to various host-derived and tumor-derived paracrine factors, delivered through the blood circulation. Previous data from our lab has shown that an increased signaling of Interleukin-15 (IL-15) results in enhanced oxidative capacity, promotion of a more oxidative phenotype and attenuation of muscle fatigue. This effect of IL-15 has yet to be characterized in a cancer-induced model of muscle dysfunction. Therefore, through this project, we sought to establish an ex-vivo working model for muscle exposure to tumor cell conditioned media using an IL-15TG overexpressing IL-15 mouse model; thereby allowing to test IL-15's role in the JAK/STAT signaling pathway, an oncogenic signaling cascade that exerts tumor-intrinsic and tumor-extrinsic effects. Current studies investigating the role of tumor secreted factors on muscle function in-vitro do so by exposing muscle cells to solutions containing tumor cell conditioned media. However, this is an incomplete representation and assessment of the in-vivo system. In our improved model, the whole extensor digitorum longus (EDL) muscles are used in combination with human breast cancer cell line conditioned media (CM). We hypothesized that the cancer cell-secreted factors will induce muscle dysfunction and affect mediators of the JAK/STAT pathway in comparison to control unconditioned media (UCM). Our initial analyses using the EDL muscles from WT mice, IL-15TG littermate control mice, and IL-15TG overexpressing IL-15 mice revealed no significant differences in the functional output in either CM or UCM conditions. However, recent literature suggests that at least a 2 hour pre-incubation period is needed to see analogous effects seen with a shared circulation of cancer cell-secreted factors and muscle cells in-vivo. Additional experiments using an extended exposure are needed to improve the translational potential of the proposed model. However, our western blot analyses revealed a statistical significance (p<0.05) in the phosphorylated STAT3 (pSTAT3) in the stimulated CM compared to the stimulated UCM conditions in the TG group. This finding is supported in the literature and suggests that samples that undergo stimulation and are exposed to CM show a higher phosphorylation of STAT3. It also validates the overexpressing properties of the IL-15TG mouse since IL-15 binding is known to induce and activate the JAK3/STAT3 pathway. In conclusion, this research provides support for further development of this ex-vivo muscle exposure to tumor cell conditioned media model.

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