Single Cell RNA-Sequencing Reveals a Murine Gallbladder Cell Transcriptome Atlas During the Process of Cholesterol Gallstone Formation

Effects of Extracellular Matrix Changes Induced by a High-Fat Diet on Gallbladder Smooth Muscle Dysfunction

BACKGROUND

Gallstone formation is a common digestive ailment, with unclear mechanisms underlying its development. Dysfunction of the gallbladder smooth muscle (GSM) may play a crucial role, particularly with a high-fat diet (HFD). This study aimed to investigate the effects of an HFD on GSM and assess how it alters contractility through changes in the extracellular matrix (ECM).

METHODS

Guinea pigs and C57BL/6 mice were fed either an HFD or normal diet (ND). Primary cultures of their (guinea pigs) gallbladder smooth muscle cells (GSMCs) were used for in vitro experiments. Histological stains, RNA-sequencing, bioinformatics analysis, three-dimensional tissue culture, real-time polymerase chain reaction (PCR), Western blot, atomic force microscopy, and muscle tension measurements were performed.

RESULTS

Histological evidence indicated structural changes in the gallbladder muscle layer and ECM collagen deposition in the HFD group. The HFD group also showed increased expression of collagen, integrin family, and matrix metalloproteinase (MMP) and the phosphoinositide 3-kinase (PI3K)-protein kinase B (PKB/Akt) signaling pathway. Compared with GSMCs cultured on Matrigel containing 1 mg/mL of collagen I, those cultured with 2 mg/mL showed a phenotype change from contractile to synthetic cells. Consistent with these findings, the HFD group also demonstrated increased ECM stiffness and decreased smooth muscle contractility.

CONCLUSIONS

Our findings reveal a mechanism by which an HFD alters the ECM composition of the gallbladder muscle, activating the integrin/PI3K-Akt/MMP signaling pathway, thereby impacting GSMC phenotype and contractility. These insights enhance the understanding of gallstone formation mechanism and provide potential therapeutic targets to treat gallbladder dysfunction.

Inhibiting miRNA-146a suppresses mouse gallstone formation by regulating LXR/megalin/cubilin-media cholesterol absorption

Background

miRNA has been implicated in regulating cholesterol homeostasis, a critical factor in gallstone formation. Here, we focused on elucidating the role of miR-146a in this pathological process.

Methods

C57BL/6 mice were fed with lithogenic diet (LD) and injected with miR-146 antagomir (anta-146) via the tail vein for various weeks. The gallbladders and liver tissues were collected for cholesterol crystal imaging, gallstone mass quantification, and molecular analysis. Levels of cholesterol, bile salt, phospholipids, and metabolic parameters in serum and bile were assessed by ELISA. A 3' UTR reporter gene assay was used to verify the direct target genes for miR-146. The relative expression of metabolism genes was analyzed by quantitative real-time PCR and immunoblotting.

Results

miR-146a-5p expression was reduced in mice and clinical samples with gallstones. Anta-146 treatment effectively prevented LD-induced gallstone formation in mice without hepatic and cholecystic damage. The mice treated with anta-146 exhibited beneficial alterations in bile cholesterol and bile acids and lipid levels in the blood. A key biliary cholesterol transporter-Megalin was identified as a direct target of miR-146. Anta-146 administration upregulated megalin expression, thereby ameliorating impaired gallbladder cholesterol absorption associated with the LXR-megalin/cubilin pathway.

Conclusion

The data demonstrates that miR-146 modulates gallbladder cholesterol absorption by targeting megalin, and prevents the pathogenesis of cholesterol gallstones.

Functional relevance of MMP2 promoter variants in gallbladder cancer: A case-control study in an Eastern Indian Population

Gallbladder cancer (GBC) is a prevalent and deadly form of bile duct cancer, associated with poor prognosis. This study aimed to investigate the genetic factors contributing to the high incidence of GBC in certain geographical regions, particularly in the Northern and Eastern parts of India. The present case-control study focused on MMP2, a gene involved in tumor progression and metastasis, as a potential candidate in GBC pathogenesis. We scanned MMP2 promoter for twelve SNPs using Sanger's sequencing and carried out a case-control study in 300 cases and 300 control samples. We found five rare variants (rs1961998763, rs1961996235, rs1391392808, rs1488656253, and rs17859816) and one nonpolymorphic SNP (rs17859817). Our results revealed a significant association between GBC and MMP2 promoter SNPs, rs243865 (Allelic-Padjusted = 0.0353) and g.55477735G > A (Allelic-Padjusted = 9.22E-05). Moreover, the haplotype "C-C-A-C-C" exhibited a significant association with GBC (P = 4.23E-05). Genotype-phenotype correlation for variant rs243865, in the GBC patient tissue samples, established that 'T' risk allele carriers had higher expression levels of MMP2. Additionally, luciferase reporter assay in HEK293T cells revealed the probable regulatory role of rs243865 variant allele 'T' in MMP2 expression. Our study uncovers the association of MMP2 promoter SNPs with GBC and their role in regulating its expression.

Resident Fibroblast MKL1 Is Sufficient to Drive Pro-fibrogenic Response in Mice

Fibrosis is an evolutionarily conserved pathophysiological process serving bifurcated purposes. On the one hand, fibrosis is essential for wound healing and contributes to the preservation of organ function. On the other hand, aberrant fibrogenic response may lead to tissue remodeling and precipitate organ failure. Recently lineage tracing studies have shown that resident fibroblasts are the primary mediator of fibrosis taking place in key organs such as the heart, the lungs, and the kidneys. Megakaryocytic leukemia 1 (MKL1) is transcriptional regulator involved in tissue fibrosis. Here we generated resident fibroblast conditional MKL1 knockout (CKO) mice by crossing the Mkl1^f/f mice to the Col1a2-Cre^ERT2 mice. Models of cardiac fibrosis, pulmonary fibrosis, and renal fibrosis were reproduced in the CKO mice and wild type (WT) littermates. Compared to the WT mice, the CKO mice displayed across-the-board attenuation of fibrosis in different models. Our data cement the pivotal role MKL1 plays in tissue fibrosis but point to the cellular origin from which MKL1 exerts its pro-fibrogenic effects.