Sex-specific differences in direct osteoclastic versus indirect osteoblastic effects underlay the low bone mass of Pannexin1 deletion in TRAP-expressing cells in mice

Abstract

Pannexin1 (Panx1) is a hemichannel-forming protein that participates in the communication of cells with the extracellular space. To characterize the role of osteoclastic Panx1 on bone, Panx1 fl/fl ;TRAP-Cre (Panx1 ΔOc ) mice were generated, and compared to Panx1 fl/fl littermates at 6 weeks of age. Total and femoral BMD was ~20% lower in females and males whereas spinal BMD was lower only in female Panx1 ΔOc mice. μCT analyses showed that cortical bone of the femoral mid-diaphysis was not altered in Panx1 ΔOc mice. In contrast, cancellous bone in the distal femur and lumbar vertebra was significantly decreased in both female and male Panx1 ΔOc mice compared to Panx1 fl/fl controls and was associated with higher osteoclast activity in female Panx1 ΔOc mice, with no changes in the males. On the other hand, vertebral bone formation was decreased for both sexes, resulting from lower mineral apposition rate in the females and lower mineralizing surface in the males. Consistent with an osteoclastic effect in female Panx1 ΔOc mice, osteoclast differentiation with RANKL/M-CSF and osteoclast bone resorbing activity in vitro were higher in female, but not male, Panx1 ΔOc mice, compared to Panx1 fl/fl littermates. Surprisingly, although Panx1 expression was normal in bone marrow stromal-derived osteoblasts from male and female Panx1 ΔOc mice, mineral deposition by male (but not female) Panx1 ΔOc osteoblasts was lower than controls, and it was reduced in male Panx1 fl/fl osteoblasts when conditioned media prepared from male Panx1 ΔOc osteoclast cultures was added to the cell culture media. Thus, deletion of Panx1 in TRAP-expressing cells in female mice leads to low bone mass primarily through a cell autonomous effect in osteoclast activity. In contrast, our evidence suggests that changes in the osteoclast secretome drive reduced osteoblast function in male Panx1 ΔOc mice, resulting in low bone mass.

Sex‐dependent role of Pannexin 1 in regulating skeletal muscle and satellite cell function

“…This raises the possibility that at least part of the skeletal muscle phenotype observed in the global Panx1 KO mice could result from Panx1 deletion in cells other than skeletal muscle. More recently, it has been reported that Panx1 has sex‐dependant roles in regulating the number of osteoclasts, cells required for bone resorption (Deosthale et al, 2022).…”

Pannexins in the musculoskeletal system: new targets for development and disease progression

“… 115 This evidence suggests that alterations in the osteoclast secretome lead to reduced osteoblast function and low bone mass in male Panx1-deficient mice. 115 …”

“…114 McCutcheon et al found that both female and male Panx1-deficient mice had significantly reduced cancellous bone in the distal femur and lumbar spine, with higher osteoclast activity observed in female Panx1-deficient mice, while there was no change in males. 115 Conversely, Panx1-deficient mice exhibited higher osteoclast differentiation and in vitro osteoclast bone resorption activity. 115 This evidence suggests that alterations in the osteoclast secretome lead to reduced osteoblast function and low bone mass in male Panx1-deficient mice.…”

“… 115 Conversely, Panx1-deficient mice exhibited higher osteoclast differentiation and in vitro osteoclast bone resorption activity. 115 This evidence suggests that alterations in the osteoclast secretome lead to reduced osteoblast function and low bone mass in male Panx1-deficient mice. 115 …”

Potential Implications of Exercise Training on Pannexin Expression and Function

“…Interestingly, TRAP-specific Panx1 KO mice (osteoclast cells) had higher rates of bone resorption, reduced formation, and a resultant lower trabecular bone mass in female mice [82]. This would suggest PANX1 function in osteoclasts is necessary to ensure proper coupling between bone formation and resorption, while in osteocytic-specific Panx1 KO mice, bone mineral density, after reaching skeletal maturity, is higher in female KO mice than in wild-type mice.…”