Phenotype of the first mouse model of Cole Carpenter Syndrome
b KU Leuven, Angiogenesis and Vascular Metabolism -VIB, Leuven, Belgium Background/Introduction: Proliferation and matrix synthesis by growth plate chondrocytes are essential for proper bone development. To fulfill these anabolic functions in an avascular environment, chondrocytes need to be metabolically adapted to this nutrient-restricted microenvironment. Purpose: Our single-cell transcriptomic profiling of neonatal growth plates shows that glucose metabolism via the pentose phosphate
... se phosphate pathway (PPP) increases with chondrocyte maturation. Generally, the PPP is considered to regulate redox homeostasis and cell proliferation through the synthesis of NADPH and ribose-5phosphate for nucleotide synthesis, but its role in chondrocytes is completely unknown. Methods: To determine whether and how the PPP in chondrocytes regulates endochondral ossification, we deleted glucose-6-phosphate dehydrogenase (G6PDH), the rate-limiting enzyme of the PPP, in these cells using Col2-Cre mice (G6pdh chon-). Results: G6pdh chonmice had shorter long bones at post-natal day (PD) 3 as evidenced by decreased tibia length (-20%; n=15; pb0.001). Histological analysis of the tibia at PD3 showed smaller growth plates (-18%; n=15; pb0.001) with disorganization of the columnar and hypertrophic zone. The observed hypocellularity (-25%; n=8; pb0.01) was not due to decreased proliferation, assessed by BrdU incorporation. Instead, we detected only in G6pdh chonmice pronounced cell death in the central region of the growth plate, analyzed by TUNEL staining (n=11). This central region stained also positive for ATF4 in G6pdh chonmice (n=8), indicative for an activated unfolded protein response and impaired protein homeostasis. Ex vivo evidence of proteostasis disturbance was provided by increased expression of genes involved in endoplasmic-reticulum associated protein degradation (ERAD), including Edem1 (+20%; n=6-9; pb0.01) and Man1a2 (+25%; n=6-9; pb0.05). Conclusion(s): Taken together, the PPP controls chondrocyte survival and protein homeostasis, which are both critical for normal growth plate organization and bone lengthening.