title: Release of skeletal muscle peptide fragments identifies individual proteins degraded during insulin deprivation in type 1 diabetic humans and mice.
abstract: Insulin regulates skeletal muscle protein degradation, but the types of proteins being degraded in vivo remain to be determined due to methodological limitations. We present a method to assess the types of skeletal muscle proteins that are degraded by extracting their degradation products as low-molecular weight (LMW) peptides from muscle samples. High-resolution mass spectrometry was used to identify the original intact proteins that generated the LMW peptides, which we validated in rodents and then applied to humans. We deprived insulin from insulin-treated streptozotocin (STZ) diabetic mice for 6 and 96 h and for 8 h in type 1 diabetic humans (T1D) for comparison with insulin-treated conditions. Protein degradation was measured using activation of autophagy and proteasome pathways, stable isotope tracers, and LMW approaches. In mice, insulin deprivation activated proteasome pathways and autophagy in muscle homogenates and isolated mitochondria. Reproducibility analysis of LMW extracts revealed that ∼80% of proteins were detected consistently. As expected, insulin deprivation increased whole body protein turnover in T1D. Individual protein degradation increased with insulin deprivation, including those involved in mitochondrial function, proteome homeostasis, nDNA support, and contractile/cytoskeleton. Individual mitochondrial proteins that generated more LMW fragment with insulin deprivation included ATP synthase subunit-γ (+0.5-fold, P = 0.007) and cytochrome c oxidase subunit 6 (+0.305-fold, P = 0.03). In conclusion, identifying LMW peptide fragments offers an approach to determine the degradation of individual proteins. Insulin deprivation increases degradation of select proteins and provides insight into the regulatory role of insulin in maintaining proteome homeostasis, especially of mitochondria.
authors.affiliation: Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota;
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Robinson
authors.affiliation: Department of Health Sciences Research, Mayo Clinic, Rochester, Minnesota; and.
authors.forename: Surendra
authors.initials: S
authors.lastname: Dasari
authors.affiliation: Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota;
authors.forename: Helen
authors.initials: H
authors.lastname: Karakelides
authors.affiliation: Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota.
authors.forename: H Robert
authors.initials: HR
authors.lastname: Bergen
authors.affiliation: Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota; nair.sree@mayo.edu.
authors.forename: K Sreekumaran
authors.initials: KS
authors.lastname: Nair
mesh_terms: D000328:Adult; D000818:Animals; D001343:Autophagy; D003285:Contractile Proteins / Q000096:biosynthesis / Q000235:genetics; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D003922:Diabetes Mellitus, Type 1 / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000172:deficiency*; D051379:Mice; D008810:Mice, Inbred C57BL; D008931:Mitochondria, Muscle / Q000378:metabolism; D008970:Molecular Weight; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000235:genetics
chemical_list: D003285:Contractile Proteins; D007328:Insulin; D009124:Muscle Proteins; D010446:Peptide Fragments; D046988:Proteasome Endopeptidase Complex
keywords: autophagy; isotope tracer; low molecular weight; method; peptidomics