Bone fragility and decline in stem cells in prematurely aging DNA repair deficient trichothiodystrophy mice

Trichothiodystrophy (TTD) is a rare, autosomal recessive nucleotide excision repair (NER) disorder caused by mutations in components of the dual functional NER/basal transcription factor TFIIH. TTD mice, carrying a patient-based point mutation in the Xpd gene, strikingly resemble many features of the human syndrome and exhibit signs of premature aging. To examine to which extent TTD mice resemble the normal process of aging, we thoroughly investigated the bone phenotype. Here, we show that female TTD mice exhibit accelerated bone aging from 39 weeks onwards as well as lack of periosteal apposition leading to reduced bone strength. Before 39 weeks have passed, bones of wild-type and TTD mice are identical excluding a developmental defect. Albeit that bone formation is decreased, osteoblasts in TTD mice retain bone-forming capacity as in vivo PTH treatment leads to increased cortical thickness. In vitro bone marrow cell cultures showed that TTD osteoprogenitors retain the capacity to differentiate into osteoblasts. However, after 13 weeks of age TTD females show decreased bone nodule formation. No increase in bone resorption or the number of osteoclasts was detected. In conclusion, TTD mice show premature bone aging, which is preceded by a decrease in mesenchymal stem cells/osteoprogenitors and a change in systemic factors, identifying DNA damage and repair as key determinants for bone fragility by influencing osteogenesis and bone metabolism

Functions of the osteocyte network in the regulation of bone mass

Osteocytes establish an extensive intracellular and extracellular communication system via gap-junction-coupled cell processes and canaliculi throughout bone and the communication system is extended to osteoblasts on the bone surface. The osteocyte network is an ideal mechanosensory system and suitable for mechanotransduction. However, the overall function of the osteocyte network remains to be clarified, since bone resorption is enhanced by osteocyte apoptosis, which is followed by a process of secondary necrosis attributable to the lack of scavengers. The enhanced bone resorption is caused by the release of intracellular content, including immunostimulatory molecules that activate osteoclastogenesis through the canaliculi. Therefore, a mouse model is required in which the osteocyte network is disrupted but in which no bone resorption is induced, in order to evaluate the overall functions of the osteocyte network. One such model is the BCL2 transgenic mouse, in which the osteocyte network, including both intracellular and extracellular networks, is disrupted. Another model is the osteocyte-specific Gja1 knockout mouse, in which intercellular communication through gap junctions is impaired but the canalicular system is intact. Combining the findings from these mouse models with previous histological observations showing the inverse linkage between osteocyte density and bone formation, we conclude that the osteocyte network enhances bone resorption and inhibits bone formation under physiological conditions. Further, studies with BCL2 transgenic mice show that these osteocyte functions are augmented in the unloaded condition. In this condition, Rankl upregulation in osteoblasts and Sost upregulation in osteocytes are, at least in part, responsible for enhanced bone resorption and suppressed bone formation, respectively

The Effects of Sevoflurane Anesthesia and Cardiopulmonary Bypass on Renal Function in Cyanotic and Acyanotic Children Undergoing Cardiac Surgery

Background: There are few data on the effects of anesthesia and cardiopulmonary bypass (CPB) on perioperative renal function in children with cyanotic congenital heart disease undergoing open heart surgery. This study aims to investigate the perioperative renal function in cyanotic versus acyanotic children undergoing sevoflurane anesthesia for open heart surgery. Methods: After receiving ethical committee approval, 12 acyanotic patients (preoperative oxygen saturation: SaO(2) > 85%) and 12 cyanotic children (SaO(2) < 85%) were included. Sevoflurane was administered at concentration levels of 2% before CPB and 1-2% during CPB after standard anesthesia induction. Inorganic fluoride, electrolytes, creatinine, urea nitrogen in serum and urine samples, and N-acetyl-beta-D-glucosaminidase (NAG) in urine samples were measured before induction, before CPB, during CPB, after CPB, at the end of surgery, and at 24th h postoperatively. Results: The levels of serum uric acid levels were higher in the cyanotic group (p < 0.05). There were no differences in the levels of serum creatinine and urine creatinine, urea nitrogen, and electrolytes between the two groups. Serum inorganic fluoride levels were always higher in the acyanotic group than in the cyanotic group, but these differences between the groups reached statistical significance at two measurement times (before CPB and end of surgery) (p < 0.05). Urinary inorganic fluoride levels increased with time in both groups. Although urinary NAG increased significantly after the CPB in the cyanotic group, the differences between the two groups did not reach statistical significance. Conclusions: We have concluded that renal function was not affected during open heart surgery with sevoflurane anesthesia, in both cyanotic and acyanotic children.WoSScopu