Knee Joint Tissues Effectively Separate Mixed Sized Molecules Delivered in a Single Bolus to the Heart

Lucy Ngo,Lillian E Knothe,Melissa L Knothe Tate

doi:10.1038/s41598-018-28228-w

Abstract

The role of molecular size selectivity in the onset and progression of osteoarthritis (OA), a degenerative disease of the musculoskeletal system and the most common cause of disability in aging adults, is unknown. Here we delivered a mixture of Texas-red (70 kDa), and Rhodamine-green (10 kDa) tagged, dextrans of neutral charge in a single bolus via heart injection to middle aged (8–10 months) and aged (17–19 months) Dunkin-Hartley Guinea pigs, a natural model for OA. We quantified tracer transport in serial-sectioned, cryofixed block specimens after five minutes’ circulation. A remarkable separation of the molecules was observed in serial fluorescent images of whole joint sections. The larger, 70 kDa red tracer was abundant in the marrow cavity albeit less prevalent or absent in the bone, cartilage, meniscus and other tissues of the joint. Tissues of the meniscus, ligament, and tendon exhibited abundant 10 kDa tracer; volumes of tissue containing this molecular tracer were significantly lower in older than in younger animals. Surprisingly, muscle fiber bundles exhibited little fluorescence, while their bounding fasciae fluoresced either red or green. Small caliber channels through the articular cartilage appeared to show a degree of green fluorescence not observed in the surrounding cartilage matrix. This study opens up new avenues for study of musculoskeletal physiology in health and disease as well as new strategies for drug delivery.

Highlights

It is currently unknown whether the bounding layers of bone and cartilage actively modulate transport into and out of tissue compartments of the joint and musculoskeletal system
The expression of ZO-1 proteins by periosteal cells[8] may implicate tight junctions as a means to control permeability across the periosteum, the outer bounding envelope of all bone surfaces not covered in cartilage
A recent study implicates the relative balance of two tight cell-cell adhesion architectures (‘zippers’ that seal surfaces and ‘buttons’ that enable controlled infiltration of lymph under controlled flow or pressure gradients) as a putative means to control relative drainage of interstitial fluid via the lymphatic system, in particular during development, and inphysiology[9]

Summary

Introduction

It is currently unknown whether the bounding layers of bone and cartilage (periosteum, subchondral bone) actively modulate transport into and out of tissue compartments of the joint and musculoskeletal system. A recent study implicates the relative balance of two tight cell-cell adhesion architectures (‘zippers’ that seal surfaces and ‘buttons’ that enable controlled infiltration of lymph under controlled flow or pressure gradients) as a putative means to control relative drainage of interstitial fluid via the lymphatic system, in particular during development, and in (patho-)physiology[9]. Assessment of the transport to/from and between tissue compartments via blood and interstitial fluid flow necessitates the use of an imaging modality that allows for seamless imaging of transport across organ, tissue, cellular and molecular length scales. We aimed to quantify differences in transport between tissue compartments of the knee joint, to test the hypothesis that boundary tissues exhibit molecular size dependent barrier properties similar to those observed in the brain, lung and gut

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