Alternatively spliced MBNL1 isoforms exhibit differential influence on enhancing brown adipogenesis

Area of Science:

• Cell Biology
• Molecular Biology
• Metabolic Regulation

Background:

• White adipocytes (WAs) can undergo browning to become beige cells, exhibiting thermogenesis similar to brown adipocytes (BAs) and contributing to metabolic homeostasis.
• Alternative splicing (AS) is crucial for cellular differentiation and function, but its role in WA browning remains underexplored.

Purpose of the Study:

• To investigate the impact of alternative splicing regulation on white adipocyte browning.
• To identify key genes and mechanisms involved in the browning process.

Main Methods:

• Comparative analysis of gene expression and splicing profiles in brown adipose tissues (BATs) during development.
• In vitro browning of pre-WAs (3T3-L1 cells) and analysis of muscleblind-like 1 (MBNL1) splicing.
• Investigating the autoregulatory mechanism of MBNL1 exon 5 exclusion involving CCUG motifs and RNA-binding motif protein 4a (RBM4a).
• Overexpression studies of different MBNL1 isoforms (MBNL1_7 and MBNL1_1) to assess their effects on cellular programming and adipogenic signatures.

Main Results:

• A distinct shift in MBNL1 splicing, from MBNL1 isoform 7 (MBNL1+ex5) to MBNL1 isoform 1 (MBNL1-ex5), was observed during BAT development and in vitro WA browning.
• MBNL1 autoregulatorily controls its own exon 5 exclusion via CCUG motifs, a process also mediated by RBM4a.
• Overexpression of MBNL1 isoform 1 had a more pronounced effect than isoform 7 on regulating MBNL1 transcripts and beige cell-specific splicing events.
• Both MBNL1 isoforms differentially enhanced beige adipogenic signatures in 3T3-L1 cells.

Conclusions:

• MBNL1 plays a significant role in regulating the browning of white adipocytes.
• The autoregulatory mechanism involving MBNL1 splicing is crucial for beige cell development.
• MBNL1 isoforms differentially influence beige adipogenesis, highlighting AS as a key regulator of thermogenesis and metabolic homeostasis.