The Viability of Perilabyrinthine Osteocytes: A Quantitative Study Using Bulk‐Stained Undecalcified Human Temporal Bones

Abstract

Bone remodeling is highly inhibited around the inner ear space, most likely by the anti-resorptive action of the inner ear cytokine osteoprotegerin (OPG) entering perilabyrinthine bone through the lacuno-canalicular porosity (LCP). This extracellular signaling pathway depends on the viability of individual osteocytes. The objective of this study was to evaluate the patency of the LCP at different ages. Sixty-five bulk-stained undecalcified human temporal bones and 19 ribs were selected to span the ages from the 30th gestational week to 95 years. Osteocytes from inside a 2-mm wide perilabyrinthine zone of bone were identified by 3D vector calculations and the numerical densities estimated with an optical dissector and compared to age-matched ribs. From a high fetal count of 90,000 cells/mm 3 , the density of viable capsular osteocytes declined rapidly to 73,000 cells/mm 3 at three years of age, and non-viable osteocytes increased inversely. After 3 years, this decline/increase continued at a much slower rate. The densities of viable as well as non-viable osteocytes and the rates of change were much higher in perilabyrinthine bone compared to ribs. Only after the age of 80 years had the density of viable capsular osteocytes declined to the level of ribs. The bi-phasic osteocyte kinetics reflects different development stages. The high initial density of viable osteocytes may secure a life-long anatomical route for inner-ear OPG despite the unique accumulation of non-viable osteocytes. Clustering of non-viable osteocytes may cause local aberrations in the signaling system by closure of the LCP.

Medication-related osteonecrosis of the jaws after tooth extraction in senescent female mice treated with zoledronic acid: microtomographic, histological and immunohistochemical characterization

“…However, osteocyte apoptosis is essential to replace damaged bone [67]. When osteocytes age, some of these cells die, though in areas of low bone turnover, such as ear bones, empty lacunae do not necessarily indicate necrotic bone [71]. In aged bone, senescent osteocytes will actually increase their number of dendritic processes [69,77], indicating increases in regulation of bone homeostasis.…”

Ratio of mitochondrial to nuclear DNA affects contamination estimates in ancient DNA analysis

“…This assumption, of different metabolic activity resulting in different mt/nc ratios could also be applied to other skeletal elements, the petrous bone in particular. In the cortical part of the petrous bone, bone remodelling is suppressed compared to surrounding tissue by a specific signalling-pathway, and the number of metabolic active osteoclasts and osteoblasts is reduced 28 . Furthermore, the more compact bone regions contain a higher number of osteocytes, which have lower numbers of mitochondria 29 .…”

Quantifying the osteocyte network in the human skeleton

“…Although some osteocytes, such as those in the inner ear, may exist for as long as human life [38], the majority are regularly removed and replaced due to the renewal of the bone matrix during remodelling. Parfitt [25, Table 7] estimated the average skeletal remodelling rate (Rem.R) to be 7.6%/year (combining both cortical and trabecular turnover rates).…”