|M.Sc Student||Plotnikov Maria|
|Subject||Cannabinoids and Post-Natal Skeletal Growth|
|Department||Department of Medicine||Supervisor||Dr. Gila Maor|
|Full Thesis text|
Postnatal skeleton presents two major physiologic processes: bone remodeling, which determines the skeletal architecture and strength, and bone growth, which determines body dimensions. Post-natal growth proceeds through endochondral ossification - a process whereby cartilage in the skeletal growth plates of long bones is exchanged by bone. Interference of cartilage-to-bone transition leads to growth retardation. These processes are regulated by a multiple genetic factors, hormones, local growth factors and environment and nutrition conditions. One of the main local factors that governs skeletal growth rate is endogenous cannabinoids system (ECS), that down regulates linear elongation of the skeleton. The actions of 9-tetrahydrocannabinol (THC), the major psychoactive component of marijuana and hashish are mediated through CB1 and CB2 cannabinoid receptors.
Our research was aimed at studying the mechanisms responsible for the EC-induced growth retardation, and to elucidate the regulatory mechanisms involved in this activity.
The research is based on an in vitro model of chondrogenesis. Neonatal mandibular condyle-derived chondrocytes, cultured under supporting conditions, undergo spontaneous chondrogenesis processes. We studied the influences of THC and AM 251and SR 144528 - specific antagonists of CB1 and CB2 respectively on chondrogenesis to establish mechanisms of EC growth inhibition.
THC as a non-specific agonist of CB1 and CB2 decreased chondrocyte proliferation rate, the expression of differentiation factors like type II collagen, aggrecan and type X collagen expressed at the maturation phase. THC also decreased the expression of IGF1 receptor-responsible for the major chondrogenesis regulatory mechanism.
Using CB1and CB2 specific inhibitors, we found that CB1 and CB2 receptors participate in down regulation of type II collagen expression and secretion. CB2 is also involved in aggrecan secretion slowdown. So we can assume that EC system is strongly involved in modulating chondrocyte differentiation processes.
ECs, through both CB1 and CB2, down regulate chondrocyte maturation. Activation of both CB1 and CB2 lead to decrease of expression and secretion of type X collagen.
CB2 is also involved in delayed onset of osteogenic processes as indicated by down regulation of type I collagen-essential for osteoid biosynthesis.
Regarding EC activities on local regulatory growth factors, we have found that ECs apparently are not involved in Ihh/PTHrP axis modulation.
However, ECs through both CB1 and CB2 remarkably decreased levels of IGF1R, one of the chondrogenesis key factors.
We assume that EC system, mediated by its both receptors: CB1 and CB2, is strongly involved in down regulation of all stages of chondrogenesis, most probably by hindering the activity of the IGF1/IGF1 receptor axis.