Bacterial Inhibition of Phosphatidylcholine Synthesis Triggers Apoptosis in the Brain

Abstract

Streptococcus pneumoniae is the most common cause of bacterial meningitis of high mortality and morbidity. Neurological sequelae include paralysis, mental retardation, and learning disorders. In humans, neurons of the hippocampus undergo apoptosis as a result of meningitis. Phosphatidylcholine (PtdCho) is an essential component of mammalian cell membranes and PtdCho deficiency, either due to chemicals or altered nutrition, leads to apoptosis, especially in hippocampal neurons. We show that apoptosis of a variety of brain cells after pneumococcal infection arises from inhibition of PtdCho biosynthesis, the first such activity described for a bacterium. Apoptosis inhibitors did not prevent the bacterial-dependent inhibition of PtdCho biosynthesis. Supplementation with exogenous lyso-phosphatidylcholine prevents cell death and treatment of mice with cytidine diphosphocholine attenuates hippocampal damage during meningitis, even after the onset of infection. We conclude that bacterial inhibition of PtdCho biosynthesis activates an apoptotic cascade that is a causative event in pathogenesis and amenable to therapeutic intervention.

Cell Wall-Mediated Neuronal Damage in Early Sepsis

“…S. pneumoniae serotype 4, strain TIGR4 (44), or unencapsulated strain R6 was grown on tryptic soy agar (Difco, Detroit, MI) plates supplemented with 3% defibrinated sheep blood or in defined semisynthetic casein liquid medium supplemented with 0.5% yeast extract (45). Mutants of TIGR4 lacking pneumolysin (ply), pyruvate oxidase (spxB), or both were created by insertion-duplication mutagenesis as previously described (40,56). Erythromycin (1 g/ml; Sigma) was added to the growth medium of the mutants as appropriate.…”

Proapoptotic effects of P. aeruginosa involve inhibition of surfactant phosphatidylcholine synthesis

“…Of note, the kinetics for decreased PtdCho synthesis in response to PA103 preceded activation of programmed cell death, because PtdCho synthesis was reduced within 1 h prior to stimulation of PARP cleavage. These findings, together with those of others, suggest that bacterial inhibition of PtdCho synthesis may be an important contributor to programmed cell death (29).…”

“…A key feature of bacterial pathogens is their ability to disrupt membrane phospholipid integrity during programmed cell death (28,29). These studies demonstrate for the first time that during the apoptotic program in pulmonary epithelia, a virulent strain of P. aeruginosa inhibits PtdCho synthesis via caspase-dependent cleavage of a key enzyme required for phospholipid synthesis.…”

“…Streptococcus pneumoniae initiates apoptosis in neuronal cells and A549 cells, the latter a transformed airway epithelial cell line, via inhibition of PtdCho synthesis (29). However, these effects appear to be due to inhibition of the activity of CPT, the terminal enzyme within the PtdCho synthetic pathway (29). Other noninfectious, pro-apoptotic agents also decrease CPT activity, leading to inhibition of PtdCho synthesis (24,31).…”

“…P. aeruginosa secretes enzymes that exhibit phospholipase A 2 -like activity, and indeed, this may be a contributing mechanism during the early phases of bacterial infection (20,30). Streptococcus pneumoniae initiates apoptosis in neuronal cells and A549 cells, the latter a transformed airway epithelial cell line, via inhibition of PtdCho synthesis (29). However, these effects appear to be due to inhibition of the activity of CPT, the terminal enzyme within the PtdCho synthetic pathway (29).…”