Gulp1 deficiency augments bone mass in male mice by affecting osteoclasts due to elevated 17β‐estradiol levels

Abstract

The engulfment adaptor phosphotyrosine‐binding domain containing 1 (GULP1) is an adaptor protein involved in the engulfment of apoptotic cells via phagocytosis. Gulp1 was first found to promote the phagocytosis of apoptotic cells by macrophages, and its role in various tissues, including neurons and ovaries, has been well studied. However, the expression and function of GULP1 in bone tissue are poorly understood. Consequently, to determine whether GULP1 plays a role in the regulation of bone remodeling in vitro and in vivo, we generated Gulp1 knockout (KO) mice. Gulp1 was expressed in bone tissue, mainly in osteoblasts, while its expression is very low in osteoclasts. Microcomputed tomography and histomorphometry analysis in 8‐week‐old male Gulp1 KO mice revealed a high bone mass in comparison with male wild‐type (WT) mice. This was a result of decreased osteoclast differentiation and function in vivo and in vitro as confirmed by a reduced actin ring and microtubule formation in osteoclasts. Gas chromatography‐mass spectrometry analysis further showed that both 17β‐estradiol (E2) and 2‐hydroxyestradiol levels, and the E2/testosterone metabolic ratio, reflecting aromatase activity, were also higher in the bone marrow of male Gulp1 KO mice than in male WT mice. Consistent with mass spectrometry analysis, aromatase enzymatic activity was significantly higher in the bone marrow of male Gulp1 KO mice. Altogether, our results suggest that GULP1 deficiency decreases the differentiation and function of osteoclasts themselves and increases sex steroid hormone‐mediated inhibition of osteoclast differentiation and function, rather than affecting osteoblasts, resulting in a high bone mass in male mice. To the best of our knowledge, this is the first study to explore the direct and indirect roles of GULP1 in bone remodeling, providing new insights into its regulation.

Ginsenoside Rb2 exhibits therapeutic value for male osteoporosis in orchiectomy mice by suppressing osteoclastogenesis and modulating NF-κB/MAPK signaling pathways

“…31,45 It has been observed that sex steroid deficiency, including lower testosterone and estrogen levels, has a significant influence on bone turnover especially osteoclasts and bone resorption, which is closely linked to the GULP1, Hif1α and CMKLR1 factors. 46–48 Additionally, it has been revealed that bone loss in orchiectomy rats was accompanied by increased RANKL, which could be counteracted by the RANKL inhibitor osteoprotegerin. 49 In this study, mice subjected to orchiectomy experienced severe bone loss 8 weeks after the surgery, which was mitigated by Rb2 treatment.…”

GULP1 deficiency reduces adipogenesis and glucose uptake via downregulation of PPAR signaling and disturbing of insulin/ERK signaling in 3T3‐L1 cells

“…Each organ was isolated from male wild-type or Gulp1 knockout mice at 8 weeks of age, lysed with Qiagen TissueLyser II, and reacted with TRIzol reagent to extract total RNA (Kim et al, 2023). Total RNA from 3T3-L1 cells was also extracted using TRIzol reagent.…”

“…Total RNA from 3T3-L1 cells was also extracted using TRIzol reagent. RT-PCR and qPCR were conducted as previously described (Kim et al, 2023). All primer sets used for both RT-PCR and qPCR are listed in Supporting Information S1: Table 2.…”