The alphavirus Sindbis virus (SINV) causes
encephalomyelitis in mice.
Lipid-containing membranes, particularly
cholesterol and
sphingomyelin (SM), play important roles in virus entry, RNA replication,
glycoprotein transport, and budding. Levels of SM are regulated by sphingomyelinases (SMases).
Acid SMase (ASMase) deficiency results in the
lipid storage disease
type A Niemann-Pick disease (
NPD-A), mimicked in mice by interruption of the ASMase gene. We previously demonstrated that ASMase-deficient mice are more susceptible to fatal SINV
encephalomyelitis, with increased viral replication, spread, and neuronal death. To determine the mechanisms by which ASMase deficiency enhances SINV replication, we compared
NPD-A fibroblasts (NPAF) to normal human fibroblasts (NHF). NPAF accumulated
cholesterol- and
sphingolipid-rich late endosomes/lysosomes in the perinuclear region. SINV replication was faster and reached higher titer in NPAF than in NHF, and NPAF died more quickly. SINV
RNA and
protein synthesis was greater in NHF than in NPAF, but virions budding from NPAF were 26 times more infectious and were regular dense particles whereas virions from NHF were larger particles containing substantial amounts of CD63. Cellular regulation of alphavirus morphogenesis is a previously unrecognized mechanism for control of virus replication and spread.