Ultrastructural Characteristics of DHA-Induced Pyroptosis

Deron R Herr,Wei-Yi Ong,Sally Shuxian Koh,Wan Shun Daniel Tan,Ting Yu Amelia Yam,Kanokporn Chayaburakul,Wai Shiu Fred Wong

doi:10.1007/s12017-019-08586-y

Deron R Herr, Wei-Yi Ong + Show 5 more

Open Access

https://doi.org/10.1007/s12017-019-08586-y

Copy DOI

Abstract

Microglial cells are resident macrophages of the central nervous system (CNS) that respond to bioactive lipids such as docosahexaenoic acid (DHA). Low micromolar concentrations of DHA typically promote anti-inflammatory functions of microglia, but higher concentrations result in a form of pro-inflammatory programmed cell death known as pyroptosis. This study used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to investigate the morphological characteristics of pyroptosis in BV-2 microglial cells following exposure to 200 µM DHA. Vehicle-treated cells are characterized by extended processes, spine-like projections or 0.4 to 5.2 µm in length, and numerous extracellular vesicles (EVs) tethered to the surface of the plasma membrane. In contrast to vehicle-treated cells, gross abnormalities are observed after treating cells with 200 µM DHA for 4 h. These include the appearance of numerous pits or pores of varying sizes across the cell surface, structural collapse and flattening of the cell shape. Moreover, EVs and spines were lost following DHA treatment, possibly due to release from the cell surface. The membrane pores appear after DHA treatment initially measured ~ 30 nm, consistent with the previously reported gasdermin D (GSDMD) pore complexes. Complete collapse of cytoplasmic organization and loss of nuclear envelope integrity were also observed in DHA-treated cells. These processes are morphologically distinct from the changes that occur during cisplatin-induced apoptosis, such as the appearance of apoptotic bodies and tightly packed organelles, and the maintenance of EVs and nuclear envelope integrity. Cumulatively, this study provides a systematic description of the ultrastructural characteristics of DHA-induced pyroptosis, including distinguishing features that differentiate this process from apoptosis.

Highlights

Pyroptosis is an inflammatory form of programmed cell death (PCD) typically associated with an antimicrobial response to infection by intracellular pathogens
The cisplatin-mediated response occurs at a slower rate, showing no apparent morphological change at 1 h (Fig. 1e), some evidence of process retraction and apoptotic morphology at 2 h (Fig. 1f), and widespread apoptosis only at 4 h (Fig. 1g)
To further confirm our previous observation that the docosahexaenoic acid (DHA)-mediated response was due to the activation of pyroptosis (Srikanth et al 2018), we evaluated DHA-treated cells for cleavage of Gasdermin D (Gsdmd), a hallmark of pyroptosis (Aglietti et al 2016)

Summary

Introduction

Pyroptosis is an inflammatory form of programmed cell death (PCD) typically associated with an antimicrobial response to infection by intracellular pathogens This process is triggered by recognition of conserved microbial features by host pattern recognition receptors (PRRs) that are expressed by immune antigen-presenting cells of the monocyte/macrophage lineage (Liu and Lieberman 2017). This leads to activation of protein complexes known as inflammasomes (Poh et al 2019), and activation of inflammatory caspases, including caspase-1 and caspase-11 (caspase-4/-5 in humans) (Miao et al 2011; Shi et al 2014). Besides being an important component of the innate immune system, pyroptosis has been shown to be involved in sterile inflammatory processes (Barrington et al 2017; Poh et al 2019)

Methods

Results

Conclusion