Reduced primary cilia length and altered Arl13b expression are associated with deregulated chondrocyte Hedgehog signaling in alkaptonuria.
Alkaptonuria (AKU) is a rare inherited disease resulting from a deficiency of the enzyme homogentisate 1,2-dioxygenase which leads to the accumulation of homogentisic acid (HGA). AKU is characterized by severe cartilage degeneration, similar to that observed in osteoarthritis. Previous studies suggest that AKU is associated with alterations in cytoskeletal organization which could modulate primary cilia structure/function. This study investigated whether AKU is associated with changes in chondrocyte primary cilia and associated Hedgehog signaling which mediates cartilage degradation in osteoarthritis. Human articular chondrocytes were obtained from healthy and AKU donors. Additionally, healthy chondrocytes were treated with HGA to replicate AKU pathology (+HGA). Diseased cells exhibited shorter cilia with length reductions of 36% and 16% in AKU and +HGA chondrocytes respectively, when compared to healthy controls. Both AKU and +HGA chondrocytes demonstrated disruption of the usual cilia length regulation by actin contractility. Furthermore, the proportion of cilia with axoneme breaks and bulbous tips was increased in AKU chondrocytes consistent with defective regulation of ciliary trafficking. Distribution of the Hedgehog-related protein Arl13b along the ciliary axoneme was altered such that its localization was increased at the distal tip in AKU and +HGA chondrocytes. These changes in cilia structure/trafficking in AKU and +HGA chondrocytes were associated with a complete inability to activate Hedgehog signaling in response to exogenous ligand. Thus, we suggest that altered responsiveness to Hedgehog, as a consequence of cilia dysfunction, may be a contributing factor in the development of arthropathy highlighting the cilium as a novel target in AKU.
Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, London, United Kingdom.
Stephen D
http://orcid.org/0000-0002-4707-7756
SD
Thorpe
Dipartimento di Biotecnologie, Chimica e Farmacia, Università degli Studi di Siena, Siena, Italy.
Silvia
S
Gambassi
Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, London, United Kingdom.
Clare L
CL
Thompson
Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, London, United Kingdom.
Charmilie
C
Chandrakumar
Dipartimento di Biotecnologie, Chimica e Farmacia, Università degli Studi di Siena, Siena, Italy.
Annalisa
A
Santucci
Institute of Bioengineering, School of Engineering and Materials Science, Queen Mary University of London, London, United Kingdom.
Martin M
MM
Knight
D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D008841:Actin Cytoskeleton / Q000378:metabolism / Q000473:pathology; D000474:Alkaptonuria / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002358:Cartilage, Articular / Q000378:metabolism* / Q000473:pathology; D016022:Case-Control Studies; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D002923:Cilia / Q000378:metabolism / Q000473:pathology; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism*; D006713:Homogentisic Acid / Q000494:pharmacology; D006801:Humans; D008024:Ligands; D000072081:Patched-1 Receptor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000071676:Zinc Finger Protein GLI1 / Q000235:genetics / Q000378:metabolism
C400551:GLI1 protein, human; D053823:Hedgehog Proteins; D008024:Ligands; C000606236:PTCH1 protein, human; D000072081:Patched-1 Receptor; D000071676:Zinc Finger Protein GLI1; D020727:ADP-Ribosylation Factors; C530391:ARL13B protein, human; D006713:Homogentisic Acid
Hedgehog signaling; actin; alkaptonuria; chondrocyte; primary cilium