Large-scale death of retinal astrocytes during normal development is non-apoptotic and implemented by microglia

PLoS Biol. 2019 Oct 18;17(10):e3000492. doi: 10.1371/journal.pbio.3000492. eCollection 2019 Oct.

Abstract

Naturally occurring cell death is a fundamental developmental mechanism for regulating cell numbers and sculpting developing organs. This is particularly true in the nervous system, where large numbers of neurons and oligodendrocytes are eliminated via apoptosis during normal development. Given the profound impact of death upon these two major cell populations, it is surprising that developmental death of another major cell type-the astrocyte-has rarely been studied. It is presently unclear whether astrocytes are subject to significant developmental death, and if so, how it occurs. Here, we address these questions using mouse retinal astrocytes as our model system. We show that the total number of retinal astrocytes declines by over 3-fold during a death period spanning postnatal days 5-14. Surprisingly, these astrocytes do not die by apoptosis, the canonical mechanism underlying the vast majority of developmental cell death. Instead, we find that microglia engulf astrocytes during the death period to promote their developmental removal. Genetic ablation of microglia inhibits astrocyte death, leading to a larger astrocyte population size at the end of the death period. However, astrocyte death is not completely blocked in the absence of microglia, apparently due to the ability of astrocytes to engulf each other. Nevertheless, mice lacking microglia showed significant anatomical changes to the retinal astrocyte network, with functional consequences for the astrocyte-associated vasculature leading to retinal hemorrhage. These results establish a novel modality for naturally occurring cell death and demonstrate its importance for the formation and integrity of the retinal gliovascular network.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Animals, Newborn
  • Astrocytes / cytology*
  • Astrocytes / drug effects
  • Astrocytes / metabolism
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Blood Vessels / metabolism
  • Blood Vessels / physiopathology
  • Cell Communication
  • Cell Count
  • Cell Death / genetics*
  • Diphtheria Toxin / toxicity
  • Gene Expression Regulation, Developmental
  • Genes, Reporter
  • Glial Fibrillary Acidic Protein / genetics
  • Glial Fibrillary Acidic Protein / metabolism
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Microglia / cytology*
  • Microglia / drug effects
  • Microglia / metabolism
  • PAX2 Transcription Factor / genetics
  • PAX2 Transcription Factor / metabolism
  • Receptor, Platelet-Derived Growth Factor alpha / genetics
  • Receptor, Platelet-Derived Growth Factor alpha / metabolism
  • Retina / cytology*
  • Retina / drug effects
  • Retina / metabolism
  • Retinal Hemorrhage / genetics
  • Retinal Hemorrhage / metabolism
  • Retinal Hemorrhage / physiopathology
  • SOX9 Transcription Factor / genetics
  • SOX9 Transcription Factor / metabolism
  • Signal Transduction
  • Vascular Endothelial Growth Factor A / genetics
  • Vascular Endothelial Growth Factor A / metabolism

Substances

  • Bacterial Proteins
  • Diphtheria Toxin
  • Glial Fibrillary Acidic Protein
  • Luminescent Proteins
  • PAX2 Transcription Factor
  • Pax2 protein, mouse
  • SOX9 Transcription Factor
  • Sox9 protein, mouse
  • Vascular Endothelial Growth Factor A
  • glial fibrillary astrocytic protein, mouse
  • vascular endothelial growth factor A, mouse
  • yellow fluorescent protein, Bacteria
  • Receptor, Platelet-Derived Growth Factor alpha