title: Effect of calpain and proteasome inhibition on Ca2+-dependent proteolysis and muscle histopathology in the mdx mouse.
abstract: Dystrophin deficiency is the underlying molecular cause of progressive muscle weakness observed in Duchenne muscular dystrophy (DMD). Loss of functional dystrophin leads to elevated levels of intracellular Ca(2+), a key step in the cellular pathology of DMD. The cysteine protease calpain is activated in dystrophin-deficient muscle, and its inhibition is regarded as a potential therapeutic approach. In addition, previous work has shown that the ubiquitin-proteasome system also contributes to muscle protein breakdown in dystrophic muscle and, therefore, also qualifies as a potential target for therapeutic intervention in DMD. The relative contribution of calpain- and proteasome-mediated proteolysis induced by increased Ca(2+) levels was characterized in cultured muscle cells and revealed initial Ca(2+) influx-dependent calpain activity and subsequent Ca(2+)-independent activity of the ubiquitin-proteasome system. We then set out to optimize novel small-molecule inhibitors that inhibit both calpain as well as the 20S proteasome in a cellular system with impaired Ca(2+) homeostasis. On administration of such inhibitors to mdx mice, quantitative histological parameters improved significantly, in particular with compounds strongly inhibiting the 20S proteasome. To investigate the role of calpain inhibition without interfering with the ubiquitin-proteasome system, we crossed mdx mice with transgenic mice, overexpressing the endogenous calpain inhibitor calpastatin. Although our data show that proteolysis by calpain is strongly inhibited in the transgenic mdx mouse, this calpain inhibition did not ameliorate muscle histology. Our results indicate that inhibition of the proteasome rather than calpain is required for histological improvement of dystrophin-deficient muscle. In conclusion, we have identified novel proteasome inhibitors that qualify as potential candidates for pharmacological intervention in muscular dystrophy.
authors: Santhera Pharmaceuticals (Switzerland) Ltd, Hammerstrasse 47, CH-4410 Liestal, Switzerland.
authors: Alexandre
authors: A
authors: Briguet
authors: Michael
authors: M
authors: Erb
authors: Isabelle
authors: I
authors: Courdier-Fruh
authors: Patrizia
authors: P
authors: Barzaghi
authors: Gesa
authors: G
authors: Santos
authors: Holger
authors: H
authors: Herzner
authors: Cyrille
authors: C
authors: Lescop
authors: Hervé
authors: H
authors: Siendt
authors: Marco
authors: M
authors: Henneboehle
authors: Philipp
authors: P
authors: Weyermann
authors: Josef P
authors: JP
authors: Magyar
authors: Judith
authors: J
authors: Dubach-Powell
authors: Günther
authors: G
authors: Metz
authors: Thomas
authors: T
authors: Meier
mesh_terms: D000818:Animals; D002118:Calcium / Q000009:adverse effects*; D002135:Calcium-Binding Proteins / Q000096:biosynthesis; D002154:Calpain / Q000037:antagonists & inhibitors*; D002478:Cells, Cultured; D006801:Humans; D051379:Mice; D018101:Mice, Inbred mdx; D008822:Mice, Transgenic; D009132:Muscles / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D020388:Muscular Dystrophy, Duchenne / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*; D032446:Myoblasts / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D011480:Protease Inhibitors / Q000627:therapeutic use*; D061988:Proteasome Inhibitors
chemical_list: D002135:Calcium-Binding Proteins; D009842:Oligopeptides; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; C033668:calpastatin; D002154:Calpain; D002118:Calcium