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. 2021 Nov 11:8:764024.
doi: 10.3389/fcvm.2021.764024. eCollection 2021.

Loss of Hepatic Surf4 Depletes Lipid Droplets in the Adrenal Cortex but Does Not Impair Adrenal Hormone Production

Xiaole Chang  1 , Yongfang Zhao  1 , Shucun Qin  1 , Hao Wang  1 , Bingxiang Wang  1 , Lei Zhai  1 , Boyan Liu  1 , Hong-Mei Gu  2 , Da-Wei Zhang  2
Affiliations

Loss of Hepatic Surf4 Depletes Lipid Droplets in the Adrenal Cortex but Does Not Impair Adrenal Hormone Production

Xiaole Chang et al. Front Cardiovasc Med. .

Erratum in

Abstract

The adrenal gland produces steroid hormones to play essential roles in regulating various physiological processes. Our previous studies showed that knockout of hepatic Surf4 (Surf4LKO) markedly reduced fasting plasma total cholesterol levels in adult mice, including low-density lipoprotein and high-density lipoprotein cholesterol. Here, we found that plasma cholesterol levels were also dramatically reduced in 4-week-old young mice and non-fasted adult mice. Circulating lipoprotein cholesterol is an important source of the substrate for the production of adrenal steroid hormones. Therefore, we investigated whether adrenal steroid hormone production was affected in Surf4LKO mice. We observed that lacking hepatic Surf4 essentially eliminated lipid droplets and significantly reduced cholesterol levels in the adrenal gland; however, plasma levels of aldosterone and corticosterone were comparable in Surf4LKO and the control mice under basal and stress conditions. Further analysis revealed that mRNA levels of genes encoding enzymes important for hormone synthesis were not altered, whereas the expression of scavenger receptor class B type I (SR-BI), low-density lipoprotein receptor (LDLR) and 3-hydroxy-3-methyl-glutaryl-CoA reductase was significantly increased in the adrenal gland of Surf4LKO mice, indicating increased de novo cholesterol biosynthesis and enhanced LDLR and SR-BI-mediated lipoprotein cholesterol uptake. We also observed that the nuclear form of SREBP2 was increased in the adrenal gland of Surf4 LKO mice. Taken together, these findings indicate that the very low levels of circulating lipoprotein cholesterol in Surf4LKO mice cause a significant reduction in adrenal cholesterol levels but do not significantly affect adrenal steroid hormone production. Reduced adrenal cholesterol levels activate SREBP2 and thus increase the expression of genes involved in cholesterol biosynthesis, which increases de novo cholesterol synthesis to compensate for the loss of circulating lipoprotein-derived cholesterol in the adrenal gland of Surf4LKO mice.

Keywords: LDL receptor (LDLR); LDL–cholesterol; atherosclerosis; cholesterol; proprotein convertase subtilisin/kexin 9; triglyceride.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
The effect of hepatic knockout of Surf4 on plasma lipids and the adrenal gland. (A–E) Plasma lipid levels. Blood samples were collected from 4-week-old mice (A,B) fasted for 10 h or 14-week-old mice fasted for 10 h and refed for 4 h (C–E). Plasma levels of total cholesterol (TC), triglycerides (TG), and HDL cholesterol (HDL-C) were measured using their specific enzymatic kits (n ≥ 6). Non-HDL-C was calculated by subtracting HDL-C from TC. (F,G) Representative images of the adrenal glands of Surf4Flox (F) and Surf4LKO mice (G) (green frame). Similar results were observed in other mice. (H) Ratio of the adrenal weight to the body weight of the same mouse. Values of all data were mean ± S.D. The significance was defined as ****p < 0.0001 and P > 0.05, no significance (ns.).
Figure 2
Figure 2
Impact of lacking hepatic Surf4 on the adrenal gland. (A) H&E staining of adrenal sections. (B,C) Oil Red O of adrenal sections. Representative figures were shown. Similar results were obtained in other mice. The images of Oil Red O staining were quantified using ImageJ (C) (8 mice per group). Data were analyzed by a Student's t-test (p < 0.0001) and a Mann Whitney test (p = 0.0002). (D–F) Adrenal total cholesterol (D), cholesteryl ester (E), and free cholesterol (F) levels. Lipids were extracted from mouse adrenal glands using the MTBE method and then subjected to total cholesterol and free cholesterol measurement using their specific enzymatic kit. Cholesteryl ester levels were calculated by subtracting free cholesterol from total cholesterol. Values of all data were mean ± S.D. The significance was defined as *p < 0.05 and ****p < 0.0001, p > 0.05, no significance (ns.).
Figure 3
Figure 3
Impact of lacking hepatic Surf4 on plasma levels of adrenal hormones. (A–C) Plasma adrenal hormone levels. Blood samples were collected from non-fasted mice [Surf4Flox (Flox) and Surf4LKO (LKO) mice, 10–14-week-old]. Aldosterone (A), corticosterone (B), and DHEA (C) were measured using their specific ELISA kits. (D) qRT-PCR. Total RNAs were extracted from adrenal glands and then subjected to qRT-PCR. The relative mRNA levels were the ratio of the target's mRNA levels indicated to that of Gapdh at the same condition (n = 4). Values of all data were mean ± S.D. p > 0.05 was defined as no significant difference (ns.).
Figure 4
Figure 4
Plasma levels of adrenal steroid hormones. (A–C) Fasting plasma hormone levels. Mice were fasted for 12 h, and blood samples were collected for the measurement of corticosterone (A), aldosterone (B), and DHEA (C) with their specific ELISA kits. (D) Plasma corticosterone levels. Mice fasted for 12 h were subjected to cold stimulation (4°C). Blood samples were collected at the indicated time points. Plasma corticosterone levels were measured using its specific ELISA kit (n = 6). Values of all data were mean ± S.D. p > 0.05 was defined as no significant difference (ns.).
Figure 5
Figure 5
The expression of genes involved in cholesterol metabolism. (A,B) qRT-PCR. The relative mRNA levels were the ratio of the target's mRNA levels indicated to that of Gapdh at the same condition. (C,D) Immunoblotting. The same amount of adrenal homogenate was applied to Western Blot using antibodies as indicated. Representative figures were shown. The densitometry was assessed. The relative densitometry is the densitometry of each target to that of actin in the same sample (C). (E) Plasma levels of ACTH. Mice (10–12-week-old, male) were fasted for 12 h. Plasma was then collected and subjected to the measurement of ACTH using an ELISA kit. Values of all data were mean ± S.D. The significance was defined as *p < 0.05, **p < 0.01, ***p < 0.001, and ****p < 0.0001. p > 0.05 was defined as no significant difference (ns.).
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References

    1. Ito M, Ye X, Wang Q, Guo L, Hao D, Howatt D, et al. . SR-BI (Scavenger Receptor BI), not LDL (Low-Density Lipoprotein) receptor, mediates adrenal stress response-brief report. Arterioscler Thromb Vasc Biol. (2020) 40:1830–7. 10.1161/ATVBAHA.120.314506 - DOI - PMC - PubMed
    1. Kraemer FB, Khor VK, Shen WJ, Azhar S. Cholesterol ester droplets and steroidogenesis. Mol Cell Endocrinol. (2013) 371:15–9. 10.1016/j.mce.2012.10.012 - DOI - PMC - PubMed
    1. Lyraki R, Schedl A. Adrenal cortex renewal in health and disease. Nat Rev Endocrinol. (2021) 17:421–34. 10.1038/s41574-021-00491-4 - DOI - PubMed
    1. Johnson BM, DeBose-Boyd RA. Underlying mechanisms for sterol-induced ubiquitination and ER-associated degradation of HMG CoA reductase. Semin Cell Dev Biol. (2018) 81:121–8. 10.1016/j.semcdb.2017.10.019 - DOI - PMC - PubMed
    1. Luo J, Yang H, Song BL. Mechanisms and regulation of cholesterol homeostasis. Nat Rev Mol Cell Biol. (2020) 21:225–45. 10.1038/s41580-019-0190-7 - DOI - PubMed