Increased Tartrate-Resistant Acid Phosphatase Expression in Osteoblasts and Osteocytes in Experimental Osteoporosis in Rats

Abstract

Tartrate-resistant acid phosphatase (TRAP) is known as an osteoclast marker, but osteoblasts and osteocytes in the vicinity of bone remodeling sites also express TRAP. Cell culture studies suggest that osteoblasts endocytose osteoclastic TRAP for inactivation. To evaluate whether changes in osteoclast activity could alter TRAP expression in osteoblasts and/or osteocytes in vivo, we studied the ovariectomized and vitamin D-deficient rat (Ovx-D) and rats healing from rickets. Bone sections were analyzed for TRAP gene expression by in situ hybridization, TRAP protein by immunogold labeling, and TRAP enzyme activity using the fluorescent substrate ELF97. Osteoblasts and osteocytes close to intracortical remodeling sites and bone surfaces demonstrated TRAP, most prominently in cancellous bone and osteocytes. Intracellular TRAP was located to electron-dense vesicles with similar morphology in both cell types. Ovx-D increased osteoclast activity (p < 0.001) and ELF97+ osteocytes (p < 0.05) in cancellous bone, but no corresponding increase was observed in the osteocyte lacunar area. The level of TRAP+ vesicles in cortical osteoblasts (p < 0.01) in Ovx-D rats was also increased. Enhanced osteoclast activity was noted in healing rickets after 72 h (p < 0.05), but no differences in TRAP expression were detected in osteoblasts or osteocytes. Thus, increased osteoclast activity does not affect TRAP expression in osteoblasts and osteocytes, favoring the notion that increased TRAP in these cells is rather due to increased synthesis. Although the role of TRAP in osteoblasts and osteocytes remains elusive, we speculate that the function is related to the capability of the enzyme to regulate the phosphorylation of proteins known to be expressed by these cells.Electronic supplementary materialThe online version of this article (doi:10.1007/s00223-013-9834-3) contains supplementary material, which is available to authorized users.

White Tea Reduced Bone Loss by Suppressing the TRAP/CTX Pathway in Ovariectomy-Induced Osteoporosis Model Rats

“…Similarly, the serum CTX level is an important biomarker for bone resorption. Increased levels of TRAP and CTX were shown in OVX rats [Solberg et al, 2014]. A previous study showed that tea consumption in rats with OVX-induced bone loss can suppress the level of TRAP, one of the osteoclast-specific genes [Wu et al, 2018].…”

Identification of inhibitors of Tartrate‐resistant acid phosphatase (TRAP/ACP5) activity by small‐molecule screening

“…TRAP has been implicated as a potential drug target because of its association with several pathologies, such as bone‐associated diseases, chronic inflammation, and cancer . Several attempts to find potent and specific inhibitors for TRAP have been performed; however, the compounds found are often toxic and lack drug‐like characteristics.…”

Regulation of Bone Homeostasis by Osteocytes

“…Oste ocy ty po sia da ją takie sa me en zy my hy dro li zu ją ce, jak oste okla sty i wy kazu ją eks pre sję wi nia no opor nej fos fa ta zy kwa śnej (TRAP, ang. Tar tra te -re si stant acid pho spha ta se), en zymu uzna wa ne go za spe cy ficz ny dla oste okla stów [34,35]. In ni au to rzy jed nak nie wy ka za li eks pre sji ge nów dla wi nia no opor nej kwa śnej fos fa ta zy w oste ocy tach ko ści szczu rów pod da nej ob cią że niu [36].…”

“…Do nie daw na je dy ną do stęp ną usta lo ną li nią mysich ko mó rek o ce chach oste ocy tów by ła my sia li nia bra nes of osteocytes and their processes provide a large surface for ion exchange between bone matrix and the fluid which fills lacunae and canaliculi. Osteocytes are armed with the same hydrolytic enzymes as are osteoclasts, and express tartrate-resistant acid phosphatase, an enzyme considered specific for osteo clasts [34,35]. Some authors, however, were una ble to detect this enzyme in osteocytes from bone subjected to mechanical loading [36].…”