Abstract A062: Skeletal Muscle Selective Autophagy Receptors are induced PDAC Cachexia
Authors: Counts Brittany R. , Narasimhan Ashok , Umberger Tara S. , Doud Emma H. , Mosley Amber L. , Zimmers Teresa A. 
Published: November 2022

Cancer-induced cachexia is a hypermetabolic condition characterized by the unintentional wasting of muscle and adipose tissue, affecting over 80% of patients with pancreatic ductal adenocarcinoma (PDAC). Muscle wasting during cachexia is due to increased skeletal muscle protein degradation via ubiquitin-proteasome and autophagy-lysosome pathways. Autophagy-lysosome degradation requires delivery of cargo to the lysosome for destruction and recycling. Macroautophagy is the most prevalent component of autophagy, encompassing bulk and selective autophagy, and it requires the de novo synthesis of an autophagosome. Bulk autophagy randomly engulfs portions of the cytoplasm. Selective autophagy is mediated through selective autophagy receptors (SAR), which bind and couple cargo to the autophagosome via the general autophagy ligands LC3B and GABARAP. While an increase in the general autophagy machinery is well described in cachectic muscle, much less is known about how complexes and organelles are selectively targeted for degradation. Methods: Here, 12-week-old male C57BL/6J mice were orthotopically implanted with 1x105 KPC cells; controls underwent sham surgery. Half of the tumor-bearing mice were treated with 120 mg/kg gemcitabine and 10 mg/kg nab-paclitaxel (GemNP) at 4 and 10 days. For endpoint analysis, mice were euthanized at 14 days when KPC mice had significant body weight, muscle mass and muscle protein loss compared to SHAM controls. In our in vitro model of PDAC cachexia, KPC-conditioned media (CM) induces C2C12 myotube wasting; thus, myotubes were treated with 50% KPC-CM or control for 48hrs. Results: GemNP reduced end tumor mass by nearly 25% and prevented body weight and muscle loss. mRNAseq of gastrocnemius muscle demonstrated induction of ribosomal component gene expression, while deep proteomics revealed reduction of 30 ribosomal component proteins in KPC mice, consistent with ongoing destruction of ribosomes. Gene expression of general autophagy ligands, LC3B (2.9-fold) and GABARAP (1.6-fold), were increased in KPC mice. Gene expression for SARs associated with ribophagy (NUFIP1, 2.6-fold) and reticulophagy (Fam134b, 11.3-fold) were increased in KPC. FAM134b protein (1.8-fold) was also increased in KPC mice. SARs for lipophagy (PNPLA2, 3.2- and PNPLA8, 1.8-fold) and mitophagy (BNIP3, 4.5-fold) were induced in KPC versus SHAM, while SARs for glycophagy and ferritinophagy were similar. SQSTM1 (3.9-fold) and NBR1 (1.9-fold), general SARs for multiple organelles including aggrephagy, lysophagy, proteaphagy and pexophagy, were increased in KPC. This activation of SARs was due to tumor-induced wasting and not chemotherapy as SAR gene expression in KPC-GemNP mice was similar to SHAM controls. Finally, we also observe markers of SAR-mediated autophagy in our in vitro model of PDAC cachexia. Conclusion: These data indicate that muscle wasting in PDAC cachexia is through activation of selective autophagy of ribosomes, mitochondria, lipid droplets, endoplasmic reticulum, protein aggregates, lysosomes, peroxisomes, and proteasomes.

Citation Format: Brittany R. Counts, Ashok Narasimhan, Tara S. Umberger, Emma H. Doud, Amber L. Mosley, Teresa A. Zimmers. Skeletal Muscle Selective Autophagy Receptors are induced PDAC Cachexia [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr A062.