Ultrastructural Characteristics of DHA-Induced Pyroptosis

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.