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SRP54 mutations induce congenital neutropenia via dominant-negative effects on XBP1 splicing

Christoph Schürch1, Thorsten Schaefer1, Joëlle S Müller1

  • 1Department of Biomedicine, University Hospital Basel, University of Basel, Basel, Switzerland.

Blood
|November 23, 2020
PubMed

Insights

SRP54 deficiency causes congenital neutropenia and Shwachman-Diamond syndrome-like symptoms. Impaired XBP1 splicing in SRP54-mutant zebrafish and human cells reveals a potential therapeutic target for these disorders.

Area of Science:

  • Genetics and Molecular Biology
  • Developmental Biology
  • Hematology

Background:

  • Heterozygous de novo missense variants in SRP54 are linked to congenital neutropenia (CN) with Shwachman-Diamond syndrome (SDS)-like features.
  • A robust in vivo model is needed to study SRP54 deficiency and its associated pathologies.

Purpose of the Study:

  • To establish and characterize the first zebrafish model of SRP54 deficiency.
  • To investigate the molecular mechanisms underlying SRP54-related phenotypes, including neutropenia and pancreatic defects.
  • To explore the role of X-box binding protein 1 (XBP1) splicing in SRP54 deficiency.

Main Methods:

  • Generated and analyzed srp54 knockout (srp54-/-) and heterozygous (srp54+/-) zebrafish.
  • Injected human SRP54 messenger RNAs (mRNAs) with patient-derived mutations into zebrafish embryos.
  • Utilized human promyelocytic HL-60 cells and CD34+ hematopoietic stem and progenitor cells to assess granulocytic maturation.
  • Performed XBP1 splicing assays in srp54-mutant fish and human cells.
  • Generated xbp1 morphants and performed rescue experiments with xbp1 mRNA.

Main Results:

  • srp54-/- zebrafish exhibit embryonic lethality and multisystemic defects.
  • srp54+/- zebrafish are viable but show mild neutropenia; patient-derived SRP54 mutations exacerbate neutropenia and cause pancreatic defects.
  • Overexpression of mutated SRP54 impairs granulocytic maturation in human cell lines.
  • SRP54 deficiency impairs unconventional XBP1 splicing in both zebrafish and human cells.
  • xbp1 morphants recapitulate SRP54 deficiency phenotypes, and spliced xbp1 mRNA rescues neutropenia in srp54+/- zebrafish.

Conclusions:

  • SRP54 is essential for embryonic development and multisystem homeostasis, with neutrophils being particularly sensitive to its loss.
  • Patient phenotypes may result from dominant-negative effects of mutated SRP54 on wild-type protein function.
  • Impaired XBP1 splicing is a key mechanism in SRP54 deficiency, presenting a potential therapeutic avenue for CN and SDS-like disorders.

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