The Tm7sf2 Gene Deficiency Protects Mice against Endotoxin-Induced Acute Kidney Injury

INTRODUCTION: Tm7sf2 gene codifies for 3β-hydroxysterol Δ14-reductase, an endoplasmic reticulum resident protein involved in cholesterol biosynthesis (1, 2).

Cholesterol is an essential component of plasma membranes, and it can also contribute to multiple cellular functions or to injury response.

Connection between cholesterol metabolism and inflammation is exemplified by Tm7sf2-KO mice, that under stress conditions show an inflammatory phenotype (NF-kB activation and TNFα upregulation) (3).

In mouse skin, the loss of Tm7sf2 gene reduces cholesterol/cholesterol sulfate levels following inflammatory insults, and increases susceptibility to skin papillomas formation (4).

AIM OF THE STUDY: Investigation of the role of Tm7sf2 gene in renal cholesterol/lipid metabolism and inflammatory response, in an in vivo model of acute kidney injury induced by the administration of lipopolysaccharide (LPS).

MATERIALS AND METHODS: Male C57BL/6, Tm7sf2+/+, and Tm7sf2-/- mice were intraperitoneally injected with a single dose of LPS (5mg/Kg) or vehicle (0.9% saline) and sacrificed at selected time points.

- Blood urea nitrogen (BUN) and serum creatinine assessment

- Hematoxylin/eosin (HE), Oil Red O (ORO) stain, and immunohistochemistry on kidney sections

- Renal cortex lipid content (TLC); mRNA and protein analysis by qPCR or Western blotting, respectively

RESULTS:

Tm7sf2-null mice are protected against LPS-induced acute kidney injury without affecting kidney cholesterol levels.

Tm7sf2 insufficiency reduces renal LPS-triggered NF-κB activation and iNOS expression

Tm7sf2 deficiency reduces neutral lipids accumulation in kidney

The lack of Tm7sf2 gene leads to FXR activation

CONCLUSIONS:

- The lack of Tm7sf2 gene results in kidney endotoxin tolerance state contributing to dampen the inflammatory response generated by LPS exposure, i.e. NF-kB activation/iNOS expression

- Lower ectopic accumulation of triglycerides (TG) in KO kidney could reduce the lipotoxicity due to secondary metabolites generation

- We hypotesize that increased FXR activation in Tm7sf2-/- kidney antagonizes NF-kB/iNOS proinflammatory pathway and TG biogenesis process

## 引言
Tm7sf2基因编码3β-羟固醇Δ14-还原酶，这是一种定位于内质网的蛋白质，参与胆固醇的生物合成过程(1, 2)。

胆固醇是细胞膜的必需组成成分，同时也可参与多种细胞功能或损伤应答。

胆固醇代谢与炎症之间的关联可通过Tm7sf2基因敲除（Tm7sf2-KO）小鼠得到印证：该类小鼠在应激状态下会表现出炎症表型，包括核因子κB（NF-κB）活化以及肿瘤坏死因子α（TNFα）表达上调(3)。

在小鼠皮肤中，Tm7sf2基因的缺失会在炎症刺激后降低胆固醇/胆固醇硫酸酯水平，并增加皮肤乳头状瘤的形成易感性(4)。

## 研究目的
本研究旨在通过脂多糖（LPS）诱导的急性肾损伤体内模型，探究Tm7sf2基因在肾脏胆固醇/脂质代谢及炎症应答中的作用。

## 材料与方法
雄性C57BL/6背景的Tm7sf2野生型（Tm7sf2+/+）与敲除型（Tm7sf2-/-）小鼠，经腹腔注射单次剂量的脂多糖（5mg/kg）或溶剂（0.9%生理盐水），并在预设时间点处死小鼠。

- 血液尿素氮（BUN）与血清肌酐水平检测
- 肾脏组织切片的苏木精-伊红（HE）染色、油红O（ORO）染色以及免疫组织化学检测
- 肾皮质脂质含量测定（薄层色谱法，TLC）；分别通过实时定量聚合酶链式反应（qPCR）与蛋白质印迹法（Western blotting）进行mRNA与蛋白水平分析

## 研究结果
1. Tm7sf2基因敲除小鼠可免受脂多糖诱导的急性肾损伤，且不影响肾脏胆固醇水平。
2. Tm7sf2功能缺失可减轻脂多糖触发的肾脏NF-κB活化与诱导型一氧化氮合酶（iNOS）表达。
3. Tm7sf2基因缺失可减少肾脏内中性脂质蓄积。
4. Tm7sf2基因的缺失会导致法尼醇X受体（FXR）活化。

## 研究结论
1. Tm7sf2基因的缺失可使肾脏进入内毒素耐受状态，从而抑制脂多糖暴露引发的炎症反应，具体表现为NF-κB活化与iNOS表达受到抑制。
2. 敲除型小鼠肾脏内甘油三酯（TG）的异位蓄积减少，可降低因次级代谢产物生成引发的脂毒性。
3. 我们推测，Tm7sf2敲除小鼠肾脏中FXR活化水平升高，可拮抗NF-κB/iNOS促炎症通路以及甘油三酯生物合成过程。