The microstructure of osteocytic lacunar-canalicular system varies with age and bone mineral density in osteoporotic and osteoarthritic patients
Date
2017
Authors
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Publisher
University of Delaware
Abstract
Osteocytes form an interconnecting network in bone and play an important role in maintaining bone health. They reside in ellipsoidal spaces called lacunae and communicate with other cells by extending dendrites known as canaliculi. The osteocyte lacunar-canalicular system (LCS) also functions as a means of transporting fluid, nutrients, and signaling molecules in bones. LCS parameters, such as lacunar density, lacunar size, and the number of canaliculi emanating from individual lacunae, differ in patients and may function as indicators of bone health. While there have been ample studies providing information on the LCS of animals such as mice, quantitative data concerning human LCS is currently lacking. ☐ The osteocyte LCS from 19 osteoporotic and 6 osteoarthritic patients were quantified and compared in this study. The patients included 8 males and 17 females with age range from 51 to 95 years old. Among the osteoporotic group, 10 patients suffered fracture. Transverse sections of cortical bone, from the superior side of the femoral neck, were stained with sodium fluorescein, imaged with confocal laser scanning microscopy, and analyzed for LCS parameters. Micro-computed tomography was used to obtain the cortical bone/tissue mineral density for the same samples. ☐ The results demonstrate that the lacunar perimeter and number of canaliculi significantly increase with age for the osteoporotic group, yet tend to decrease (although not significantly) for the osteoarthritic group. Lacunar size tends to be larger in males but was not statistically different from that in females. Canalicular density (i.e., the number of canaliculi per unit length of lacunar perimeter) does not vary with age or any patient category (males vs. females, osteoporotic vs. osteoarthritic, fractured vs. non-fractured), in agreement with our previous results in mice. Interestingly, we found that the canalicular density increases with bone mineral density with a very high significance (R2 = 0.30 and p = 0.005) mainly due to the decreasing lacunar perimeter with higher bone mineral density. For our knowledge, this is the first experimental evidence that osteocytes actively sense their matrix environment in terms of mineral content and adapt their morphology accordingly. ☐ In summary, the current investigations provided much needed quantitative data on human osteocyte LCS microstructure and its relations to age, gender, and bone mineral density in a mixed patient population with osteoporosis and osteoarthritis. The intriguing finding of increased canalicular number density in denser bone matrix needs to be tested in normal human population in the future. The potential cellular and molecular mechanisms by which osteocytes sense and adapt to their environment in both healthy and disease conditions remain to be determined. This line of research will enhance our understanding of how to maintain the health of bone cells and improve bone quality in humans.
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Keywords
Biological sciences, Bone mineral density, Femoral head, Lacunar-canalicular system, Osteoarthritis, Osteocyte, Osteoporosis, mir