The Cannabinoid Receptor Type 1 Is Essential for Mesenchymal Stem Cell Survival and Differentiation: Implications for Bone Health

Figure 1

The CB₁ receptor is increased during early osteogenesis and is essential for the survival of differentiated MSCs. (a) Differentiated MSCs displayed a significant increase in CB₁ receptor mRNA expression after 2 weeks of differentiation compared to undifferentiated MSCs (**𝑃=0.002, Student’s unpaired 𝑡-test, 𝑛=5). (b) Serum withdrawal significantly reduced the metabolic function of undifferentiated MSCs (Con; **𝑃<0.01, 1-way ANOVA and Newman-Keuls, 𝑛=5). In differentiated MSCs, serum withdrawal had no effect on metabolic function, and serum deprived differentiated MSCs displayed significantly greater metabolic function compared to serum deprived undifferentiated MSCs (⁺⁺𝑃<0.01, 1-way ANOVA and Newman-Keuls, 𝑛=5). Treatment of differentiated MSCs with SR141716 (SR1, 1 μM; 24 hours) blocked the ability of differentiated MSCs to survive serum withdrawal (^££𝑃<0.01, 1-way ANOVA and Newman-Keuls, 𝑛=5). (c) Serum withdrawal induced a significant increase in the numbers of undifferentiated MSCs displaying apoptotic nuclei (Con; ***𝑃<0.001, 1-way ANOVA and Newman-Keuls, 𝑛=4) compared to undifferentiated MSCs maintained with serum. Differentiated MSCs survived serum withdrawal compared to serum deprived undifferentiated MSCs (⁺⁺⁺𝑃<0.001, 1-way ANOVA and Newman-Keuls, 𝑛=4). Treatment of differentiated MSCs with SR1 blocked the ability of differentiated MSCs to survive serum withdrawal compared to serum deprived differentiated MSCs (^£££𝑃<0.001, 1-way ANOVA and Newman-Keuls, 𝑛=4). (d) Representative images of caspase-3 activity in undifferentiated MSCs exposed to control (i) and (ii) serum withdrawal conditions and caspase-3 activity in differentiated MSCs exposed to control (iii) and serum withdrawal in the presence of SR1 (iv).