Title: Osteoblast-Osteocyte Specific Contributions of Kalirin to Dendritic Morphology
loan Anh Do (Presenter)
Indiana University School of Dentistry
Jung Min Hong, Indiana University School of Dentistry
Tyler Terhune, Indiana University School of Dentistry
Angela Bruzzaniti, Indiana University School of Dentistry
Objectives: Bone formation and regeneration are controlled by osteoblasts. Osteocytes are differentiated from mature osteoblasts that become trapped in the bone matrix. Osteocytes contain membrane extensions known as dendrites that enable osteocytes to communicate with neighboring osteocytes and to send signals that regulate the activity of osteoblasts and osteoclasts. Dendrite morphogenesis is thought to occur during the transition of late osteoblasts into early osteocytes. Disruption in osteocytes number and the dendritic network has negative effects on bone homeostasis that may lead to osteoporosis and other degenerative bone diseases. We reported that global deletion of Kalirin (Kal-KO), a multi-domain GDP/GTP-exchange factor, leads to low bone mass. The goal of this research is to understand the role of Kalirin in osteoblast-osteocyte function and its contribution to osteocyte dendrite morphogenesis.
Methods: To examine dendrite length, primary osteocytes were isolated by sequential collagenase digestion from the long bones of wild-type (WT) or Kal-KO mice which lack all three known Kalirin isoforms. In addition, we examined Kal7-KO mice, which lack only the Kalirin7 isoform that is known to regulate neuronal dendrite elongation. Osteocytes cultured in vitro were imaged and the length and number of dendrites per osteocyte was calculated using ImagePro software.
Results: Our data showed a 55.6±2.6% decrease in primary dendrite length for global Kal-KO osteocytes, compared to WTs (p-value=0.01). In addition, Kal7-KO showed a 73.86±5.29% decrease in primary dendrite length compared to WTs (p-value=0.01).
Conclusions: These results demonstrate that deletion of Kalirin results in a significant decrease in osteocyte dendrite length. Further, our studies suggest that deletion of the Kalirin7 isoform is sufficient to decrease osteocyte dendrite length. Understanding the mechanisms of dendrite elongation by Kalirin may help us develop novel ways to prevent bone loss and improve bone mass.