Abstract 969: PKC-theta modulates myosteatosis, muscle function, atrophy, and survival in murine pancreatic ductal adenocarcinoma
Authors: Rupert Joseph E. , Huot Joshua R. , Narasimhan Ashok , Jengelley Daenique H. , Bonetto Andrea , Zimmers Teresa A. 
Published: July 2021

Approximately 80% of patients with pancreatic ductal adenocarcinoma (PDAC) suffer cachexia, involuntary loss of fat and muscle due to inflammation and dysmetabolism that increases treatment toxicity, reduces treatment response and promotes mortality. Most research has focused on muscle and adipose individually while neglecting tissue crosstalk. Recently, we reported that IL6 trans-signaling from muscle to fat in PDAC cachexia augments adipose lipolysis, leading to increased muscle lipid accumulation (myosteatosis) and promoting activation of lipid sensitive signaling pathways and metabolic substrate shifts in muscle. The lipid sensitive protein kinase C theta (PKC-θ) modulates myopathic phenotypes including muscular dystrophy, atrophy, and insulin resistance. PKC-θ is activated by diacylglycerol, which binds to PKC-θ promoting its translocation to the plasma membrane, phosphorylation, and activation. Activated PKC-θ modulates pathways with known roles in muscle atrophy including inhibition of insulin signaling, activation of NF-κB, and increased shedding of the IL-6R. We used in vitro and in vivo models to study the role of PKC-θ in PDAC cachexia. Here 50,000 tumor cells of a line derived from the KPC (LSL-KrasG12D:LSL-Trp53R172H:Pdx1-Cre) genetically engineered model of PDAC were implanted in the pancreases of male C57BL/6J mice. Tissues were collected when mice displayed severe cachexia (~25% muscle loss). Phospho-Thr538-PKC-θ was increased 1.8-fold (p=0.002) in muscle of mice with KPC cachexia and phosphorylation of PKC-θ substrates was correspondingly increased (p=0.048). Plasma from KPC-tumor bearing mice was used to treat C2C12 myotubes, with or without the PKC inhibitor Sotrastaurin. After 48 hours, KPC plasma caused a significant decrease in average myotube diameter compared to no tumor plasma (18%, p=0.002), whereas addition of 500nM Sotrastaurin prevented KPC plasma-induced myotube atrophy. KPC tumor growth was not different between wildtype mice and mice with germline deletion of the PKC-θ gene, Prkcq. However, Prkcq null tumor-bearing mice demonstrated greater in vivo muscle force production (p&lt;0.01), reduced muscle loss (p&lt;0.02), larger myofiber cross-sectional area (p=0.004), and reduced total muscle protein ubiquitination (p&lt;0.0001). Prkcq null tumor-bearing mice also demonstrated increased survival versus wildtype controls (p&lt;0.001). Our data suggest that chronic lipolysis associated with PDAC promotes myosteatosis and PKC-θ activation in muscle which promotes muscle dysfunction and wasting and further that inhibition of PKC-θ in muscle may be a beneficial treatment for PDAC cachexia.

Citation Format: Joseph E. Rupert, Joshua R. Huot, Ashok Narasimhan, Daenique H. Jengelley, Andrea Bonetto, Teresa A. Zimmers. PKC-theta modulates myosteatosis, muscle function, atrophy, and survival in murine pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 969.