N88S Seipin-related Seipinopathy is a Lipidopathy Associated with Loss of Iron Homeostasis

Academic Background

Seipin is a protein encoded by the human BSCL2 gene and the yeast SEI1 gene, forming an endoplasmic reticulum (ER)-bound homo-oligomer. This oligomer plays a crucial role in targeting ER-lipid droplet (LD) contact sites, facilitating the delivery of triacylglycerol (TG) to nascent LDs. Mutations in the BSCL2 gene, particularly N88S and S90L, lead to Seipinopathy, a group of motor neuron diseases (MNDs) characterized by the misfolding of N88S Seipin into inclusion bodies (IBs) and cellular dysfunction. Although the importance of Seipin in the nervous system has been widely recognized, its molecular mechanisms remain unclear. This study aims to explore the effects of the N88S Seipin mutation on cellular lipid metabolism and iron homeostasis through quantitative untargeted mass spectrometric proteomic and lipidomic analyses, thereby revealing the pathological mechanisms of Seipinopathy.

Source of the Paper

This paper was authored by Mariana O. Ribeiro, Mafalda Oliveira, Verónica Nogueira, Vítor Costa, and Vitor Teixeira, among others, from multiple research institutions in Portugal. The paper was published in 2025 in the journal Cell Communication and Signaling, with the DOI 10.1186/s12964-024-02007-9.

Research Process and Results

1. Proteomic and Lipidomic Analysis

The study began with quantitative untargeted mass spectrometric proteomic and lipidomic analyses to compare changes in protein and lipid abundance between wild-type (WT) and N88S Seipin mutant cells. The results showed that in N88S Seipin mutant cells, the abundance of 115 proteins decreased, while the abundance of 97 proteins increased. These differentially expressed proteins were primarily involved in ion transport, phospholipid biosynthetic processes, and lipid metabolism.

2. Alterations in Lipid Metabolism

Lipidomic analysis revealed a significant increase in phosphatidic acid (PA) levels in N88S Seipin mutant cells, while levels of phosphoinositides (PIP) and phosphatidylinositol triphosphate (PIP3) in the phosphatidylinositol (PI) metabolic pathway decreased. This indicates that the N88S Seipin mutation leads to significant changes in lipid metabolism, particularly the dysregulation of phospholipid metabolism.

3. Dysregulation of Inositol Metabolism

The study further found that inositol metabolism was significantly altered in N88S Seipin mutant cells. Through the detection of the INO1-LacZ transcriptional reporter gene, it was observed that INO1 expression significantly increased in N88S Seipin mutant cells during the later growth phases (PDS and stationary phases). This suggests that the N88S Seipin mutation causes dysregulation of inositol metabolism, thereby affecting phospholipid biosynthesis.

4. Dysregulation of Iron Homeostasis

Proteomic analysis also revealed a decrease in the abundance of iron homeostasis-related proteins (such as Fit1p, Arn1p, Arn2p, and Hmx1p) in N88S Seipin mutant cells. Further studies showed that N88S Seipin mutant cells accumulated more iron during the exponential growth phase, but iron levels significantly decreased during the PDS phase. This indicates that the N88S Seipin mutation leads to dysregulation of iron homeostasis, particularly during growth phases with increased iron demand.

5. Role of MAPK Hog1p/p38

The study also explored the role of MAPK Hog1p/p38 in N88S Seipin mutant cells. The results showed that Hog1p activation was significantly increased in N88S Seipin mutant cells, particularly during the PDS phase. Deletion of Hog1p restored iron homeostasis in N88S Seipin mutant cells and enhanced Aft1p transcriptional activity. This suggests that Hog1p plays a key role in the dysregulation of iron homeostasis caused by the N88S Seipin mutation.

Conclusions and Significance

This study demonstrates that the N88S Seipin mutation not only causes protein misfolding but also significantly affects lipid metabolism and iron homeostasis. These findings provide new insights into the pathological mechanisms of Seipinopathy and reveal potential therapeutic targets and biomarkers. In particular, the dysregulation of lipid metabolism and iron homeostasis may be important pathological features of Seipinopathy, offering new directions for future therapeutic strategies.

Research Highlights

1. Significant Changes in Lipid Metabolism: The N88S Seipin mutation leads to increased phosphatidic acid (PA) levels and dysregulation of the phosphatidylinositol (PI) metabolic pathway.
2. Dysregulation of Inositol Metabolism: INO1 expression significantly increases in N88S Seipin mutant cells during later growth phases, indicating dysregulation of inositol metabolism.
3. Dysregulation of Iron Homeostasis: N88S Seipin mutant cells accumulate more iron during the exponential growth phase, but iron levels significantly decrease during the PDS phase, indicating dysregulation of iron homeostasis.
4. Role of MAPK Hog1p/p38: Hog1p activation is significantly increased in N88S Seipin mutant cells, and deletion of Hog1p restores iron homeostasis and enhances Aft1p transcriptional activity.

Additional Valuable Information

The study also found that Fet3 expression in N88S Seipin mutant cells significantly increased during the PDS phase and under iron-deficient conditions, which differs from the expression patterns of other Aft1p-regulated genes. This suggests that the N88S Seipin mutation has complex effects on the expression of Aft1p-regulated genes.

Through systematic proteomic and lipidomic analyses, this study reveals the profound impact of the N88S Seipin mutation on cellular lipid metabolism and iron homeostasis, providing new insights into the pathological mechanisms of Seipinopathy and identifying potential therapeutic targets for future strategies.