In vitro hypoxia-induced effects on the differentiation of anterior horn, central body, and posterior horn of neonatal porcine meniscus

The meniscus plays a crucial role in load transmission and shock absorption, lubrication and nutrition of the femorotibial joint (1). Meniscal regeneration still represents one of the main challenges in orthopaedic field, as detailed knowledge about meniscal biology, composition, and gene expression is still incomplete. Meniscal injuries are particularly difficult to repair due to the complex micro- and macroscopic structure of the tissue. Our recent studies on in vitro differentiation of cultured neonatal porcine menisci suggest a positive role of hypoxia in the differentiation process during meniscal maturation (2). Here we studied in vitro newborn piglet’s medial menisci subdivided into their three anatomical parts: anterior horn (A), central body (C), and posterior horn (P). We examined the effects of two different culture conditions [normoxia (21% O2) vs. hypoxia (1% O2)] on tissue morphology, cell density, gene expression, and cellular efficiency linked to glycosaminoglycans (GAGs) production in three meniscal portions. Immunohistochemical, gene expression, and biochemical analyses were performed at four different experimental time points (T0 = day of explant; T7, T10, and, T14 DIV). The hallmark signs of meniscal maturation in control conditions were a significant reduction in cell number, the acquisition of a fibrochondrocyte-like shape in the remaining cells, and an increase in GAG content in the extracellular matrix. Amongst the three portions, the anterior horn was the most sensitive to hypoxia, displaying a slower cell loss, a higher number of PCNA- and SOX9-expressing cells, and a decrease in CASP-3 gene expression (proliferating, fibrochodrocitic and apoptotic cells, respectively). This study highlights how hypoxia acts differentially on the three portions of the meniscus. Furthermore, hypoxia increases the availability of relatively undifferentiated cells, which may offer a valid source of committed progenitors to be used in meniscal repair. References (1) Peretti, G.M.; Polito U.; Di Giancamillo M; Andreis M.E.; Boschetti F.; Di Giancamillo A. Tissue Eng. Part A 2019 Jul;25(13-14):978-989. (2) Herrera Millar V.R.; Mangiavini L.; Polito U.; Canciani B.; Nguyen VT.; Cirillo F.; Anastasia L.; Peretti G.M.; Modina S.C.; DI Giancamillo A. Int. J. Mol. Sci., 2021 22(13).