Introduction: Some studies have
found that probiotics can improve cognitive impairment in Alzheimer’s disease,
although the specific molecular mechanism by which this occurs has not been
reported. Our previous research found that probiotics inhibited bacteria-related
Toll-like receptor 4- and retinoic-acid-inducible gene-I-mediated nuclear
factor-B signaling pathways to improve cognitive impairment. However,
it is unclear whether probiotics have similar effects on other pattern
recognition receptors that respond to bacteria. Methods: Nine-month-old
senescence-accelerated mouse prone 8 (SAMP8) mice received ProBiotic-4 (a mixture
of Lactobacillus acidophilus, Bifidobacterium bifidum, Lactobacillus
casei, and Bifidobacterium lactis) orally for 12 weeks. The effects on
other bacteria-related pattern recognition receptors were then
investigated. Results: ProBiotic-4-treated SAMP8 mice showed
improvement in memory deficits, synaptic and cerebral neuronal injuries, and
microglial activation. ProBiotic-4 also markedly increased the expression of
intestinal tight junction proteins (i.e., claudin-1, occludin, and zonula
occluden-1), decreased the expression of interleukin-1 at both the mRNA
and protein levels, and reduced the expression of caspase-11, cleaved caspase-1,
and -kinase 1 (ALPK1) in the intestine and brain.
Conclusions: These findings suggest that probiotics may have
therapeutic potential for the treatment of inflammation in the gut-brain axis and
for cognitive impairment. The mechanism of action of probiotics appears to be
related to inhibition of the caspase-11/caspase-1 pathway and reduction of ALPK1
expression.