Project Summary/Abstract
Increasing prevalence of Alzheimer’s dementia (AD) is a growing health and economic crisis. Although
studied for 112+ years, the root causes for sporadic AD—which is > 95% of AD—are unclear. Over the
last 15 years, 415+ clinical trials to test new drugs against AD failed. Approved drugs can only manage
symptoms. I will use NIH Pioneer funding to investigate a novel hypothesis for the etiology of sporadic
Alzheimer’s dementia, based on my insight that imbalance between two innate immune peptides may
be a key factor that modulates the risk of formation, the stability, and clearance of AD-associated fibrils
and plaques. Recent observations of chronic P. gingivalis and Herpesvirus infections being associated
with Alzheimer’s fit this hypothesis. I am, to my knowledge, the only researcher working on this idea.
The human cathelicidin LL-37, unique in our proteome, is an antiviral and antibacterial defense peptide
deployed by microglia, macrophages, neutrophils, epithelia, B cells, and NK cells (to kill infected cells).
Thus LL-37 is a centrally important defense peptide, necessary for killing bacterial and viral pathogens
and infected host cells. LL-37’s Vitamin D3-, RXR-agonist-, and butyrate-dependent expression is also
stimulated by infection, wounding, exercise, and some vaccines (e.g., BCG & OPV vaccines). Certain
pathogens, P. gingivalis in particular, release enzymatic virulence factors that rapidly degrade LL-37.
Degradation of LL-37 could well dysregulate the brain’s innate immunity, causing neurodegeneration;
in LL-37’s absence, the immune process of macroautophagy is crippled. The Alzheimer’s-associated
peptide Ab now seems also to be a host defense peptide; brain infections by either Herpesviridae or P.
gingivalis stimulate Ab production, causing it to accumulate in plaques that co-locate with pathogens.
Recently I and collaborators showed that LL-37 and Ab are both expressed in human brain, and bind
each other sequence-specifically. LL-37/Ab binding prevents fibrillization and blocks Ab from adopting
b-type secondary structure. Thus, LL-37 degradation may allow Ab to accumulate. Our in vivo studies
show that cathelicidin induction in 5XFAD mice slows AD progression and improves 5XFAD cognition
to match wild-type. I aim to tie this finding to infection-associated dementia. In this Pioneer project, I
will use wild-type and cathelicidin KO mice to demonstrate that degradation of LL-37 by P. gingivalis
virulence factors may well be one cause of brain tissue degradation leading to dementia, which can be
prevented by early upregulation of cathelicidin to prevent infection; or treated orally with antimicrobials.
My lab has developed new antimicrobials that potently kill both P. gingivalis and inactivate Herpesvirus.