Impairment of APPL1/Myoferlin facilitates adipogenic differentiation of mesenchymal stem cells by blocking autophagy flux in osteoporosis

Abstract

An imbalance of human mesenchymal stem cells (hMSCs) adipogenic and osteogenic differentiation is crucial in the pathogenesis of osteoporosis, and elucidation of the underlying mechanism is urgently needed. APPL1, an adaptor protein of the adiponectin receptor, was recently shown to be closely related to bone mass. However, the role of APPL1 in the imbalance of hMSC differentiation in osteoporosis is unclear. Therefore, we aimed to explore the mechanisms by which APPL1 alters hMSCs adipogenic differentiation in osteoporosis. Here, we found that APPL1 expression was downregulated in elderly patients with osteoporosis and in mouse osteoporosis model. APPL1 negatively regulated hMSC adipogenic differentiation in vivo and in vitro. Mechanistically, by enhancing ubiquitination-mediated Myoferlin degradation, downregulated APPL1 expression increased the risk of lysosome dysfunction during hMSCs adipogenic differentiation. Lysosomal dysfunction inhibited autophagy flux by suppressing autophagosome degradation and promoted hMSC differentiation towards the adipocyte lineage. Our findings suggest that APPL1/Myoferlin downregulation promoted hMSCs adipogenic differentiation by inhibiting autophagy flux, further impairing the balance of hMSCs adipogenic and osteogenic differentiation in osteoporosis; the APPL1/ Myoferlin axis may be a promising diagnostic and therapeutic target for osteoporosis.

Reduced APPL1 impairs osteogenic differentiation of mesenchymal stem cells by facilitating MGP expression to disrupt the BMP2 pathway in osteoporosis

“…The Co-IP results showed that APPL1 had no binding relationship with MGP on protein ( Fig. 7 A ), which is consistent with the results of liquid chromatography combined with tandem MS (LC‒MS/MS) in our previous study ( 10 ). We confirmed that APPL1 knockdown increased both the mRNA and protein levels of the MGP gene, and APPL1 overexpression decreased the mRNA and protein levels of MGP in MSCs ( Figs.…”

“…Moreover, APPL1 overexpression effectively alleviated osteoporosis and promoted osteogenic differentiation of MSCs, whereas APPL1 knockdown attenuated osteogenic differentiation of MSCs. Combined with our previous study ( 10 ), it suggests that APPL1 may be an important molecule leading to the abnormal balance of adipogenic and osteogenic differentiation of MSCs in osteoporosis.…”

“…APPL1 interacts with AdipoR and mediates p38-mitogen-activated protein kinase (MAPK) and AMP-activated protein kinase activation, thereby regulating APN signaling and downstream events ( 8 , 9 ). Our previous study verified that APPL1/myoferlin deficiency promotes adipogenic differentiation of MSCs by blocking autophagic flux in osteoporosis ( 10 ). Recent studies have shown that APPL1 is involved in regulating the osteogenic differentiation ability of MSCs.…”

“…Our previous study showed that the expression of APPL1 was downregulated in osteoporosis and that the impairment of APPL1/myoferlin facilitates adipogenic differentiation of MSCs by blocking autophagic flux ( 10 ). To further clarify the role of APPL1 in osteogenesis in osteoporosis, we successfully established a mouse model of glucocorticoid-induced osteoporosis (GIOP).…”

“…However, the role of APPL1 in osteoporosis has not yet been elucidated. Our previous study has shown that the impairment of APPL1/myoferlin facilitates adipogenic differentiation of MSCs by blocking autophagic flux in osteoporosis ( 10 ). In this study, we found that APPL1 expression was downregulated in osteoporosis patients and mice.…”