Purpose of Review Mitochondria are recognized to be one of the most important organelles in chondrocytes for their role in triphosphate (ATP) generation through aerobic phosphorylation. Mitochondria also participate in many intracellular processes involving modulating reactive oxygen species (ROS), responding to instantaneous hypoxia stress, regulating cytoplasmic transport of calcium ion, and directing mitophagy to maintain the homeostasis of individual chondrocytes. Designs To summarize the specific role of mitochondria in chondrocytes, we screened related papers in PubMed database and the search strategy is ((mitochondria) AND (chondrocyte)) AND (English [Language]). The articles published in the past 5 years were included and 130 papers were studied. Results In recent years, the integrity of mitochondrial structure has been regarded as a prerequisite for normal chondrocyte survival and defect in mitochondrial function has been found in cartilage-related diseases, such as osteoarthritis (OA) and rheumatoid arthritis (RA). However, the understanding of mitochondria in cartilage is still largely limited. The mechanism on how the changes in mitochondrial structure and function directly lead to the occurrence and development of cartilage-related diseases remains to be elusive. Conclusion This review aims to summarize the role of mitochondria in chondrocytes under the physiological and pathological changes from ATP generation, calcium homeostasis, redox regulation, mitophagy modulation, mitochondria biogenesis to immune response activation. The enhanced understanding of molecular mechanisms in mitochondria might offer some new cues for cartilage remodeling and pathological intervention.

Fibroblast growth factor 19 (FGF19) is recognized to play an essential role in cartilage development and physiology, and has emerged as a potential therapeutic target for skeletal metabolic diseases. However, FGF19-mediated cellular behavior in chondrocytes remains a big challenge. In the current study, we aimed to investigate the role of FGF19 on chondrocytes by characterizing mitochondrial biogenesis and fission–fusion dynamic equilibrium and exploring the underlying mechanism. We first found that FGF19 enhanced mitochondrial biogenesis in chondrocytes with the help of β Klotho (KLB), a vital accessory protein for assisting the binding of FGF19 to its receptor, and the enhanced biogenesis accompanied with a fusion of mitochondria, reflecting in the elongation of individual mitochondria and the up-regulation of mitochondrial fusion proteins. We then revealed that FGF19-mediated mitochondrial biogenesis and fusion required the binding of FGF19 to the membrane receptor, FGFR4, and the activation of AMP-activated protein kinase alpha (AMPKα)/peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α)/sirtuin 1 (SIRT1) axis. Finally, we demonstrated that FGF19-mediated mitochondrial biogenesis and fusion was mainly dependent on the activation of p-p38 signaling. Inhibition of p38 signaling largely reduced the high expression of AMPKα/PGC-1α/SIRT1 axis, decreased the up-regulation of mitochondrial fusion proteins and impaired the enhancement of mitochondrial network morphology in chondrocytes induced by FGF19. Taking together, our results indicate that FGF19 could increase mitochondrial biogenesis and fusion via AMPKα-p38/MAPK signaling, which enlarge the understanding of FGF19 on chondrocyte metabolism.

Osteocytes are the main sensitive cells in bone remodeling due to their potent functional cell processes from the mineralized bone matrix to the bone surface and the bone marrow. Neighboring osteocytes communicate with each other by these cell processes to achieve molecular exchange through gap junction channels. Platelet-derived growth factor-AA (PDGF-AA) has been reported to enhance bone tissue remodeling by promoting cell proliferation, migration, and autocrine secretion in osteoid cell linage. However, the effect of PDGF-AA on intercellular communication between osteocytes is still unclear. In the present study, we elucidated that PDGF-AA could enhance the formation of dendritic processes of osteocytes and the gap junctional intercellular communication by promoting the expression of connexin43 (Cx43). This modulation process was mainly dependent on the activation of phosphorylation of Akt protein by phosphatidylinositol 3-kinase (PI3K)/Akt (also known as protein kinase B, PKB) signaling. Inhibition of PI3K/Akt signaling decreased the Cx43 expression induced by PDGF-AA. These results establish a bridge between PDGF-AA and cell–cell communication in osteocytes, which could help us understand the molecular exchange between bone cells and fracture healing.

Nonsyndromic cleft lip with/without cleft palate (NSCL/P) is one of the most common human congenital defects. Rs2262251 (G>C) in long noncoding RNA (lncRNA) RP11‐462G12.2 is in high linkage disequilibrium with rs8049367, which was identified in our previous genome‐wide association study on NSCL/P, and is a potential causative single‐nucleotide polymorphism (SNP) for NSCL/P. To test these hypotheses, rs2262251 was evaluated in another cohort of 1,314 cases and 1,259 controls. Rs2262251 was associated with NSCL/P risk (p = .003). However, no association was detected for cleft palate only. SNP rs2262251 affected the structure and expression of lncRNA RP11‐462G12.2 in HEK293 and HEPM cells and in lip tissues from patients with NSCL/P. Overexpression of the rs2262251 G allele contributed to reducing the number of cells in the G0/G1 phase, inhibiting cell apoptosis, and promoting cell proliferation in vitro. The rs2262251 C allele regulated the expression of miR‐744‐5p and its target gene IQSEC2, both of which were expressed in human lip tissues, and showed reverse correlation during mouse lip development. Taken together, these findings suggest that rs2262251 is associated with the risk of NSCL/P and participates in a lncRNA–miRNA–mRNA regulatory axis in which miR‐744‐5p and IQSEC2 combine to control NSCL/P development.

Objective Non‐syndromic tooth agenesis (NSTA) may share common genetic factors with non‐syndromic cleft lip with or without cleft palate (NSCL/P). Single‐nucleotide polymorphisms (SNPs) were associated with individual's susceptibility to these anomalies. We selected five NSCL/P‐associated SNPs from our previous genome‐wide association study (GWAS) to test for the associations with NSTA. Materials and methods A total of 677 NSTA cases and 1,144 healthy controls were recruited in this case–control study. Five genome‐wide NSCL/P‐associated SNPs (rs2235371, rs7078160, rs8049367, rs4791774, and rs13041247) were genotyped by TaqMan platform and evaluated for the associations with NSTA using plink software. Results No significant associations between these SNPs and risk of NSTA were observed in the overall analysis and subgroup analysis with the number of missing teeth. However, in the subgroup analysis by tooth position, rs8049367 was nominally associated with mandibular premolar agenesis (Dominant model: ORdom = 0.66, 95% CIdom = 0.47–0.93, pdom = 0.016; Heterozygote model: ORhet = 0.60, 95% CIhet = 0.41–0.88, Phet = 0.008). Rs4791774 showed a nominal association with congenitally missing maxillary canine (Dominant model: ORdom = 0.53, 95% CIdom = 0.28–0.98, pdom = 0.041; Heterozygote model: ORhet = 0.50, 95% CIhet = 0.26–0.97, Phet = 0.041) and premolar (Additive model: OR = 0.59, 95% CI = 0.36–0.96, p = 0.035). Conclusion This study showed that NSCL/P susceptible loci rs8049367 and rs4791774 were probably associated with the risk of NSTA.