title: Insulin decreases autophagy and leads to cartilage degradation.
abstract: OBJECTIVE
  Autophagy, a key homeostasis mechanism, is defective in Osteoarthritis (OA) and Type 2 Diabetes (T2D). T2D has been proposed as a risk factor for OA. We hypothesized that diabetes impairs articular cartilage integrity by decreasing autophagy. Our objective was to investigate the effects of high glucose and insulin, characteristics of T2D, on cartilage homeostasis.
  
  
  METHODS
  Immortalized human chondrocytes (TC28a2) and primary human chondrocytes (HC) were cultured in 25 mM or 0 mM glucose and treated with insulin (10, 100, 500 nM) for 2, 6 or 24 h. Activity of LC3-II, Akt and rpS6 was evaluated by Western blotting (WB). Human cartilage explants were cultivated with 25 mM glucose and insulin (100,1000 nM) for 24 h to evaluate histopathology. MMP-13 and IL-1β expression was determined by immunohistochemistry and WB. Effects of Rapamycin (10 μM) were analyzed by WB. LC3 and rpS6 expression was determined by WB in chondrocytes from Healthy, Non Diabetic-OA and Diabetic-OA patients.
  
  
  RESULTS
  Insulin downregulates autophagy by reducing LC3 II expression and increasing Akt and rpS6 phosphorylation. Loss of proteoglycans and increased MMP-13 and IL-1β expression was observed after insulin treatment. Autophagy activation by rapamycin reversed insulin effects. Importantly, chondrocytes from diabetic-OA patients showed decreased LC3 and increased p-rpS6 expression compared to Healthy and Non-Diabetic OA patients.
  
  
  CONCLUSIONS
  These results suggest that decreased autophagy might be a mechanism by which diabetes influences cartilage degradation. Pharmacological activation of autophagy may be an effective therapeutic approach to prevent T2D-induced cartilage damage.
authors.affiliation: Grupo de Biología del Cartílago, Servicio de Reumatología, Instituto de Investigación Biomédica de A Coruña (INIBIC), Complexo Hospitalario Universitario de A Coruña (CHUAC), Spain; Centre for Neuroscience and Cell Biology and Faculty of Pharmacy, University of Coimbra, Portugal.
authors.forename: M
authors.initials: M
authors.lastname: Ribeiro
authors.affiliation: Grupo de Biología del Cartílago, Servicio de Reumatología, Instituto de Investigación Biomédica de A Coruña (INIBIC), Complexo Hospitalario Universitario de A Coruña (CHUAC), Spain.
authors.forename: P
authors.initials: P
authors.lastname: López de Figueroa
authors.affiliation: Grupo de Biología del Cartílago, Servicio de Reumatología, Instituto de Investigación Biomédica de A Coruña (INIBIC), Complexo Hospitalario Universitario de A Coruña (CHUAC), Spain.
authors.forename: F J
authors.initials: FJ
authors.lastname: Blanco
authors.affiliation: Centre for Neuroscience and Cell Biology and Faculty of Pharmacy, University of Coimbra, Portugal.
authors.forename: A F
authors.initials: AF
authors.lastname: Mendes
authors.affiliation: Grupo de Biología del Cartílago, Servicio de Reumatología, Instituto de Investigación Biomédica de A Coruña (INIBIC), Complexo Hospitalario Universitario de A Coruña (CHUAC), Spain. Electronic address: beatriz.carames.perez@sergas.es.
authors.forename: B
authors.initials: B
authors.lastname: Caramés
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001343:Autophagy / Q000187:drug effects* / Q000502:physiology; D002358:Cartilage, Articular / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000378:metabolism / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D053583:Interleukin-1beta / Q000096:biosynthesis; D053509:Matrix Metalloproteinase 13 / Q000096:biosynthesis; D008875:Middle Aged; D010003:Osteoarthritis / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D011509:Proteoglycans / Q000172:deficiency; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000502:physiology; D046509:Tissue Culture Techniques; D015854:Up-Regulation / Q000187:drug effects
chemical_list: C508585:IL1B protein, human; D007328:Insulin; D053583:Interleukin-1beta; D011509:Proteoglycans; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D053509:Matrix Metalloproteinase 13; D005947:Glucose; D020123:Sirolimus
keywords: Autophagy; Chondrocytes; Diabetes; Insulin; Osteoarthritis (OA)