Date of Graduation

12-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Health, Sport and Exercise Science (PhD)

Degree Level

Graduate

Department

Health, Human Performance and Recreation

Advisor

Tyrone Washington

Committee Member

Nicholas Greene

Second Committee Member

Michelle Gray

Third Committee Member

Jeffrey Wolchok

Keywords

Cachexia, Cancer, Fibrosis, Leucine, Sex, Skeletal Muscle

Abstract

Cancer cachexia is a multifactorial wasting syndrome characterized by losses in bodymass >5% and occurs in approximately 80% of all cancer patients. Chronic inflammation and fibrosis play roles in cancer cachexia and a greater understanding of these contributing pathways to this pathology will pave the way for potential therapeutic avenues. While inflammation and fibrosis have been researched in various models of cancer cachexia, little to no studies have been performed in both sexes as most previous studies focus on males. PURPOSE The purpose of these studies is to investigate the role of fibrosis on cancer cachexia development as well as the effects of leucine supplementation on cancer cachexia in both sexes. METHODS Lewis Lung Carcinoma cells (LLC) or PBS (control) were injected into the hind-flank of C57Bl6/J mice at 8 wks age, and tumor allowed to develop for 1, 2, 3 or 4 wks. WT and APCMin/+ mice were supplemented with regular or leucine-enriched water following weaning up until euthanasia at 20 weeks of age. Body and pertinent tissue and muscle weights were taken. Histology was used to measure CSA. RT-qPCR and immunoblotting were used for analysis of markers of fibrosis in the LLC study, and markers for inflammation, protein anabolism and catabolism, and myogenesis in the APC study. RESULTS Both male and female LLC mice exhibited increased fibrosis at the onset of cancer cachexia. Females, however, saw induction of pro-fibrotic markers such as TGFβ and Collagens 1 and 3 as early as 1wk post-injection when compared to males who saw no increases until 4wks when cachexia was developed. Male APCMin/+ mice had greater reductions in body weight following leucine supplementation whereas female APCMin/+ mice did not experience this effect of leucine. Higher elevation of IL-6 mRNA abundance accompanied the decrease in body weight in male APCMin/+ mice. Myogenesis was altered in female mice, favoring satellite cell activation and differentiation with increases in MyoD and Myogenin over quiescence. Myotube diameter was decreased following addition of blood plasma taken from male APCMin/+ mice. DISCUSSION Fibrosis clearly plays an early role in the development of cancer cachexia through upregulation of the TGF-β pathway, but timing of TGF-β and collagen induction differed between sexes. However, the canonical effectors downstream of TGF-β were not altered in either sex in the LLC time course. Supplementation of leucine exacerbated cancer cachexia in male but not female APCMin/+ mice, and elevation of inflammatory IL-6 accompanied this effect of leucine. Altered myogenesis in females suggests a protective effect from wasting in female mice and could explain the lack of reduction in myotube diameter observed in APCMin/+ female plasma treated cells. These data provide novel insight into variations in fibrosis as well as responses to nutraceutical interventions for cancer cachexia between sexes.

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