Aims
Adipocyte-derived exosomes (ADEs) stimulate the activation of macrophages and contribute to the development of insulin resistance. Sonic Hedgehog (Shh) is an exosome-carrying protein and stimulates macrophages to secrete inflammatory cytokines. However, the impact of ADEs carrying Shh on the pro-inflammatory activation of macrophages and consequently, adipocyte insulin resistance is unclear.
Background/aims
Adipocyte-derived exosomes (ADEs) stimulate the activation of macrophages and contribute to the development of insulin resistance. Sonic Hedgehog (Shh) is an exosome-carrying protein and stimulates macrophages to secrete inflammatory cytokines. However, the impact of ADEs carrying Shh on the pro-inflammatory activation of macrophages and consequently, adipocyte insulin resistance is unclear.
Conclusion
Together, these data indicate that ADEs carrying Shh induce the M1 polarization of macrophages, which contributes to insulin resistance in adipocytes through the Ptch/PI3K pathway.
Methods
3T3-L1 adipocytes were cultured with high glucose and insulin to imitate the pathogeny of insulin resistance. ADEs were isolated from conditioned media of 3T3-L1 adipocytes via differential ultracentrifugation. We explored the role of ADEs carrying Shh in the polarization of macrophages by flow cytometry. Western blot and electrophoretic mobility shift assay (EMSA) were performed to determine the activation of Shh-mediated signalling pathways. The effects of ADE-treated macrophages on adipocyte insulin signalling were studied by Western blot.
Results
We found that circulating Shh-positive exosomes were increased in type 2 diabetes patients. High glucose and insulin increased the secretion of Shh-positive ADEs. The ADEs carrying Shh induced pro-inflammatory or M1 polarization of bone marrow-derived macrophages (BMDM) and RAW 264.7 macrophages. Inhibitors of Ptch and PI3K blocked the M1 polarization induced by ADEs, which suggests that ADEs carrying Shh mediated M1 macrophage polarization through the Ptch/PI3K signalling pathway. ADE-treated RAW 264.7 macrophages were subsequently used to assess the effect on insulin signalling in adipocytes. Using a co-culture assay, we showed that both ADE-treated macrophages and exosomes from these macrophages could decrease the expression of insulin-resistant substrate-1 (IRS-1) and hormone-sensitive lipase (HSL) in adipocytes. Inhibitors of Ptch and PI3K blocked the down-regulation of IRS-1 and HSL induced by ADE-treated macrophages.