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J Biol Chem. 2015 Aug 28;290(35):21443-59. doi: 10.1074/jbc.M115.640425. Epub 2015 Jul 15.

Fibulin-4 E57K Knock-in Mice Recapitulate Cutaneous, Vascular and Skeletal Defects of Recessive Cutis Laxa 1B with both Elastic Fiber and Collagen Fibril Abnormalities.

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From the Department of Dermatology and Cutaneous Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
the Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Department of Molecular Pharmacology and Physiology, University of South Florida, Morsani College of Medicine, Tampa, Florida 33612, and.
the Department of Biochemistry, Faculty of Medicine, Oita University, Yufu, Oita 879-5593, Japan.
From the Department of Dermatology and Cutaneous Biology, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107,


Fibulin-4 is an extracellular matrix protein essential for elastic fiber formation. Frameshift and missense mutations in the fibulin-4 gene (EFEMP2/FBLN4) cause autosomal recessive cutis laxa (ARCL) 1B, characterized by loose skin, aortic aneurysm, arterial tortuosity, lung emphysema, and skeletal abnormalities. Homozygous missense mutations in FBLN4 are a prevalent cause of ARCL 1B. Here we generated a knock-in mouse strain bearing a recurrent fibulin-4 E57K homozygous missense mutation. The mutant mice survived into adulthood and displayed abnormalities in multiple organ systems, including loose skin, bent forelimb, aortic aneurysm, tortuous artery, and pulmonary emphysema. Biochemical studies of dermal fibroblasts showed that fibulin-4 E57K mutant protein was produced but was prone to dimer formation and inefficiently secreted, thereby triggering an endoplasmic reticulum stress response. Immunohistochemistry detected a low level of fibulin-4 E57K protein in the knock-in skin along with altered expression of selected elastic fiber components. Processing of a precursor to mature lysyl oxidase, an enzyme involved in cross-linking of elastin and collagen, was compromised. The knock-in skin had a reduced level of desmosine, an elastin-specific cross-link compound, and ultrastructurally abnormal elastic fibers. Surprisingly, structurally aberrant collagen fibrils and altered organization into fibers were characteristics of the knock-in dermis and forelimb tendons. Type I collagen extracted from the knock-in skin had decreased amounts of covalent intermolecular cross-links, which could contribute to the collagen fibril abnormalities. Our studies provide the first evidence that fibulin-4 plays a role in regulating collagen fibril assembly and offer a preclinical platform for developing treatments for ARCL 1B.


aneurysm; aorta; collagen; connective tissue; elastin; extracellular matrix; forelimb; lysyl oxidase; skin; tendon

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