Abnormal epiphyseal development in a feline model of Sandhoff disease

Abstract

Sandhoff disease (SD) is caused by decreased function of the enzyme β-N-acetylhexosaminidase, resulting in accumulation of GM2 ganglioside in tissues. Neural tissue is primarily affected and individuals with the infantile form of the disease generally do not survive beyond 4 years of age. Current treatments address neurometabolic deficits to improve lifespan, however, this extended lifespan allows clinical disease to become manifest in other tissues, including the musculoskeletal system. The impact of SD on bone and joint tissues has yet to be fully determined. In a feline model of infantile SD, animals were treated by intracranial injection of adeno-associated virus vectors to supply the central nervous system with corrective levels of hexosaminidase, resulting in a twofold to threefold increase in lifespan. As treated animals aged, signs of musculoskeletal disease were identified. The present study characterized bone and joint lesions from affected cats using micro-computed tomography and histology. All affected cats had similar lesions, whether or not they were treated. SD cats displayed a significant reduction in metaphyseal trabecular bone and markedly abnormal size and shape of epiphyses. Abnormalities increased in severity with age and appear to be due to alteration in the function of chondrocytes within epiphyseal cartilage, particularly the articular-epiphyseal complex. Older cats developed secondary osteoarthritic changes. The changes identified are similar to those seen in humans with mucopolysaccharidoses. Statement of clinical significance: the lesions identified will have significant implications on the quality of life of individuals whose lifespans are extended due to treatments for the primary neurological effects of SD.

Keywords: animal models; bone development; chondrocytes; gangliosidosis; growth plate.

FIGURE 1

3D reconstruction of μCT scans of the medial distal femur (left), cranial femur (center), and lateral proximal humerus (right) from a 3.9 months old unaffected control (A), 5 months old unaffected control (B), 3.9 months old affected (C), and 5 months old affected (D). Arrows indicate widened distal physes compared to controls; arrow heads indicate underdeveloped humeral head and greater tubercle, which is more visually apparent in group 1 than group 2. Distal femoral epiphysis also is remarkably decreased in size compared with that of unaffected control animals. Both humeral and femoral epiphyses contain numerous pits over the surface of the bone from affected cat (C). μCT, micro-computed tomography; FC, femoral condyle; GT, greater tubercle; H, humeral head

FIGURE 2

3D reconstruction of μCT scans of the distal femur showing cranial, caudal, medial, and distal views, as well as isolated metaphyseal trabecular bone from (A-E) a 29.7 months old unaffected control cat and (F-J) a 30.8 months old affected cat, demonstrating osteopenia of the trabecular bone (J). Red arrow heads indicate a periarticular osteophyte on the medial aspect of the femur of the affected cat; red arrows indicate subchondral cavitations; white arrow heads indicate sesamoid bones embedded into the gastrocnemius muscle (likely displaced in the affected animal due to tissue preparation) and remnants of a calcified meniscus. μCT, micro-computed tomography; FC, femoral condyle; FT, femoral trochlea

FIGURE 3

3D reconstruction of μCT scans of the intact elbow joint (cranial, lateral, and medial views) from a 29.7 months old unaffected control (A-C) and a 20.8 months old affected cat (D-F). Arrow heads indicate widening of the lateral joint space and arrows indicate periarticular osteophytes on the proximal radius and ulna. Last, the distal epiphysis of the humeri and the proximal epiphyses of the radii and ulnae of the affected animals (D) were reduced in size compared to the controls (A). μCT, micro-computed tomography; LE, lateral epicondyle; ME, medial epicondyle; OP, olecranon process; R, radius; U, ulna

FIGURE 4

Bone volume/total volume (BV/TV) and bone surface (BS) of trabecular bone within the distal femur and proximal humerus from affected cats and unaffected controls in groups 2 and 3. *P < .05 when compared to the unaffected control group, and **P < 0.01 when compared to the unaffected control group

FIGURE 5

Histological sections from the articular cartilage of distal femur of representative cats: (A) a 5 months old unaffected control; (B) a 37.2 months old unaffected control; (C) a 5 months old affected; and (D) a 30.8 months old affected cat demonstrating diffusely vacuolated chondrocytes in (C) and (D) (arrow heads). Bar = 75 μm

FIGURE 6

Histological sections from distal femur of representative cats: (A) a 5 months old unaffected control; (B) a 37.2 months old unaffected control; (C) a 5 months old affected cat demonstrating reduced trabecular bone, increased thickness of articular-epiphyseal complex (double arrows), and bone marrow hypocellularity when compared to (A); and (D) a 30.8 months old affected cat demonstrating reduced trabecular bone, bone marrow hypercellularity, retained growth plate cartilage (boxes), and lesions associated with osteoarthritis (arrow heads indicate articular cartilage fibrillation, arrow indicates periarticular osteophyte) when compared to (B). Bar = 2000 μm. FT, femoral trochlea

FIGURE 7

Histological sections from distal femora of representative cats: (A) a 5 months old affected cat with retained cartilage canal vessels (arrows) and (B) retained epiphyseal (growth plate) cartilage; (C) a 37.2 months old unaffected control cat demonstrating normal epiphyseal trabecular bone; (D) a 30.8 months old affected cat demonstrating retained growth plate cartilage within trabecular bone; (E) a 21.3 months old affected cat exhibiting retained and thickened calcified cartilage/deep epiphyseal cartilage (arrows); (F) a 30.8 months old affected cat demonstrating osteoarthritis lesions characterized by areas of articular cartilage fibrillation/degeneration (arrows). Bar in (A) = 300 μm, bars in B-F = 500 μm