Abstract
From the age of about 35 years, women gradually lose bone. Around menopause, the rate of bone loss escalates due to increased bone resorption and declining bone formation levels, rendering them more prone to develop osteoporosis. However, there are large variations in both the onset and progression of age induced bone loss and osteoporosis, and such patient-related variations can also be observed in the treatment of cancer patients with bone metastases. Interindividual variation is a well-known phenomenon in the clinic, but better tools are still needed for investigating and incorporating these differences into health sciences, to support the development of more personalized treatment strategies for bone diseases. We therefore believe that it is important to initiate studies that are closer to the clinical reality, which take into consideration how different people really are, and what significance these differences may have on their osteoclasts differentiation, their basic bone resorptive properties, as well as their sensitivity to anti-resorptive treatment. To investigate this, 49 healthy female blood donors (40 - 66 years) were recruited. Donor demographics were collected and their biomarker levels of the bone formation marker (PINP) and bone resorption marker (CTX-I) were measured. This information was compared to their monocytes’ ability to differentiate into mature osteoclasts, the in vitro differentiated osteoclasts ability to resorb bone, and their sensitivity to zoledronic acid.
1) The first two studies investigated whether aging and/or menopause induce long-term changes in osteoclast precursors, resulting in an increased ability to resorb bone. We found that monocytes are “reprogrammed” in vivo allowing them to “remember” in vitro the age, menopause status, and bone formation status resulting in more aggressive osteoclasts. An age-induced increase in the fusion-potential of osteoclasts was found to be a contributing factor for the enhanced bone resorption in vitro, but also in vivo. Our results suggested that this fusion-potential was related to expression levels of DCSTAMP and that the reprogramming of monocytes may be mediated through changes in DNA-methylation levels.
2) The third study investigated if osteoclasts generated from different healthy individuals would show a variable sensitivity to zoledronic acid in vitro, and if so, if we could explain the observed variation. We found more than a 200-fold difference in the osteoclast sensitivity to zoledronic acid in vitro. In addition, we found that osteoclasts from current smokers were less sensitive to zoledronic acid and that osteoclasts with a higher degree of nuclearity were less sensitive to treatment. Increasing protein levels of mature cathepsin K in osteoclast cultures rendered them less sensitive to zoledronic acid. Surprisingly, neither the gene nor the protein expression of farnesyl diphosphate synthase was found to be relevant for the zoledronic acid sensitivity.
3) The fourth study investigated what primes the osteoclast towards becoming a pit- or trench-forming osteoclast, and whether the prevalence of a given resorption mode is linked to the origin
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of the precursor. We found that there are substantial variations among donors in the extent of trench formation their osteoclast make, and that a high proportion of trenches was associated with smoking habits of the donor and a high number of nuclei per osteoclast. This aggressive type of resorption is not linked to the total amount of cathepsin K found in the cell, but rather the cells relative ability to convert prepro- and pro cathepsin K to mature cathepsin K.
When working with primary cell cultures it is often common practice to aim towards eliminating interindividual variations as much as possible. From this study, we conclude that both scientifically and clinically relevant information was gained, as the interindividual variations were incorporated and investigated for the primary cell cultures, instead of eliminating them. In this study, we have discovered that interindividual variations among female donors are highly relevant for their bone resorptive properties, as well as their sensitivity to zoledronic acid treatment. These results may prove to be of importance for the development of more personalized treatment strategies for bone diseases. Our data suggest that DNA methylation profiles might be a potential supplementary method for the prediction of patient sensitivity to zoledronic acid (and possibly other bisphosphonates) and for an early prediction of the individual rate of bone loss for future osteoporosis patients, enabling preventive measures.
1) The first two studies investigated whether aging and/or menopause induce long-term changes in osteoclast precursors, resulting in an increased ability to resorb bone. We found that monocytes are “reprogrammed” in vivo allowing them to “remember” in vitro the age, menopause status, and bone formation status resulting in more aggressive osteoclasts. An age-induced increase in the fusion-potential of osteoclasts was found to be a contributing factor for the enhanced bone resorption in vitro, but also in vivo. Our results suggested that this fusion-potential was related to expression levels of DCSTAMP and that the reprogramming of monocytes may be mediated through changes in DNA-methylation levels.
2) The third study investigated if osteoclasts generated from different healthy individuals would show a variable sensitivity to zoledronic acid in vitro, and if so, if we could explain the observed variation. We found more than a 200-fold difference in the osteoclast sensitivity to zoledronic acid in vitro. In addition, we found that osteoclasts from current smokers were less sensitive to zoledronic acid and that osteoclasts with a higher degree of nuclearity were less sensitive to treatment. Increasing protein levels of mature cathepsin K in osteoclast cultures rendered them less sensitive to zoledronic acid. Surprisingly, neither the gene nor the protein expression of farnesyl diphosphate synthase was found to be relevant for the zoledronic acid sensitivity.
3) The fourth study investigated what primes the osteoclast towards becoming a pit- or trench-forming osteoclast, and whether the prevalence of a given resorption mode is linked to the origin
13
of the precursor. We found that there are substantial variations among donors in the extent of trench formation their osteoclast make, and that a high proportion of trenches was associated with smoking habits of the donor and a high number of nuclei per osteoclast. This aggressive type of resorption is not linked to the total amount of cathepsin K found in the cell, but rather the cells relative ability to convert prepro- and pro cathepsin K to mature cathepsin K.
When working with primary cell cultures it is often common practice to aim towards eliminating interindividual variations as much as possible. From this study, we conclude that both scientifically and clinically relevant information was gained, as the interindividual variations were incorporated and investigated for the primary cell cultures, instead of eliminating them. In this study, we have discovered that interindividual variations among female donors are highly relevant for their bone resorptive properties, as well as their sensitivity to zoledronic acid treatment. These results may prove to be of importance for the development of more personalized treatment strategies for bone diseases. Our data suggest that DNA methylation profiles might be a potential supplementary method for the prediction of patient sensitivity to zoledronic acid (and possibly other bisphosphonates) and for an early prediction of the individual rate of bone loss for future osteoporosis patients, enabling preventive measures.
Original language | English |
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Publication status | Published - 2020 |