TABLE 1.

Key studies examining AD, MCI, sleep disturbance and/or inflammation.

Title	Author	Methods	Results	Conclusion
Human studies (AD)
Microglial markers are elevated in the prodromal phase of Alzheimer’s disease and vascular dementia	Olsson et al., 2013	CSF measured from 96 AD patients, 65 healthy controls, and 170 patients with MCI from baseline and over 5.7 years.	When stratified according to CSF levels of tau and Aβ42, YKL-40 was elevated in those with an AD-indicative profile compared with stable MCI with a normal profile. YKL-40 was significantly elevated in AD subjects and both YKL-40 and sCD14 were increased in MCI patients who converted to vascular dementia.	Biomarker of glial inflammation may be used to differentiate between AD patients, controls, and MCI. Supports microglial inflammation in AD.
Excessive daytime sleepiness and napping in cognitively normal adults: associations with subsequent amyloid deposition measured by PiB PET	Spira et al., 2018	One hundred and twenty-eight participants of the Baltimore Longitudinal Study of Aging Neuroimaging Substudy completed subjective excessive daytime sleepiness (EDS) questionnaire, PiB PET scan and MRI. Analysis focused on mean cortical DVR (index of global amyloid deposition) in the frontal, cingulate, lateral temporal, parietal, and lateral occipital regions of the brain.	Patients with EDS had more than 2.5 times the odds of having Aβ deposition an average of 15.7 years later.	Sleepiness may be related to AD pathology and contribute to Aβ deposition.
Human studies (MCI)
Inflammatory markers in AD and MCI patients with different biomarker profiles	Schuitemaker et al., 2009	Plasma serum and CSF levels of IL-6, ACT, CRP, Aβ42, p-tau, and total tau taken from 145 patients with probable AD and 67 with MCI. High to low risk MCI was established using Aβ42/tau profile.	CSF and plasma CRP levels higher in MCI patients (p < 0.01), even in those with a low-risk biomarker profile. CSF IL-6 levels higher in MCI patients with low-risk profile.	Inflammation may be involved in AD/cognitive decline before Aβ and tau pathology appears.
Animal studies
Amyloid β peptide directly impairs pineal gland melatonin synthesis and melatonin receptor signaling through the ERK pathway	Cecon et al., 2015	Adult male Wistar rats were kept under 12 h light, 12 h dark cycle. Pineal glands were harvested and then treated with Aβ1–40 or Aβ1–42 before stimulation of melatonin synthesis with noradrenaline. HEK293 cells were transfected to express melatonin receptors MT1 and MT2. After Aβ incubation, glands were processed to nuclear protein extraction and supershift assay was performed by incubating protein extracts. TNF content was measured by ELISA kits. Real-time RT-PCR, radioligand binding experiments, microplate BRET assay, and SDS-page were conducted.	Glands incubated with Aβ1–40 (75% reduction) or Aβ1–42 (40% reduction) showed impaired noradrenaline-induced NAS and melatonin production. Aanat mRNA levels were reduced in those treated with Aβ1–40. Those treated with Aβ also showed dose-dependent increases in NF-κB. Fifty-two inflammatory genes related to the TLR family, TLR adaptors, MAP kinases of the JNK family, and most cytokine-related genes were upregulated in treated glands. TNF release peaked in response to Aβ. Melatonin receptor MT1 binding sites were reduced by 40% in HEK293 cells treated with Aβ.	Aβ interferes with melatonin binding and signaling and stimulates inflammation in the pineal gland.
An impaired intrinsic microglial clock system induces neuroinflammatory alterations in the early stage of amyloid precursor protein knock-in mouse brain	Ni et al., 2019	Inflammatory and clock genes examined in microglia isolated from 2 month old male amyloid precursor protein knock-in (APP-KI) and wild-type (WT) mice using CAGE deep sequencing and PCR. Mice were kept in dark-light conditions where Zeitgeber time 0 (ZT0) was lights on and ZT12 was lights off. All mice were administered SR9009 (synthetic agonist for REV-ERB) for 14 days. Brain cortical tissues collected from APP-KI mice with and without SR9009 injection. mRNA from isolated microglia of each group at different time points subjected to RT-PCR. Locomotor activity was tested after 14 days of treatment and novel object recognition and Y-maze tests were conducted.	Expression of cortical clock genes occurred at different time points in APP-KI mice, suggesting impaired transcriptional feedback loops. mRNA expression of inflammatory genes were significantly higher in cortical microglia of APP-KI mice, particularly during ZT14. Expression of TNF-α, IL-1β, and IL-6 were significantly higher during the day in APP-KI mice. A significant increase in REV-ERBα mRNA was detected in APP-KI after treatment with SR9009. Aβ deposition were observed in hippocampus and cerebral cortex of 6 month old, but not 2 month old, APP-KI mice, but treatment with SR9009 increased expression in 2 month old APP-KI.	Expression of clock genes and pro-inflammatory genes (TNF-α, IL-1β, and IL-6) increased in microglia of APP-KI mice. Clock gene disturbance in microglia is involved in onset of AD pathology through the induction of chronic neuroinflammation.