AD Mouse Studies

"Rapamycin fed late in life extends lifespan in genetically heterogeneous mice," Harrison, 2009. (9)

This was a monumental study. Prior to this study it was well known that "inhibition of TOR signaling pathway by genetic or pharmacologic intervention extends lifespan in invertebrates, including yeast, nematodes and fruit flies". "Here was reported that rapamycin, an inhibitor of mTOR pathway extends median and maximal lifespan of both male and female mice, when fed beginning of 600 days of age. Based on age at 90% mortality, rapamycin led to an increase of 14% for females and 9% for males."..."A 600-day-old mouse is roughly the equivalent of a 60-year old person"

The finding were considered "consistent with the hypothesis that inhibiting the mTOR1 pathway retards mammalian aging." "Because incidences of most diseases rise rapidly with age, interventions that delay ageing would greatly benefit health."..."These finding have implications for further development of interventions targeting mTOR for the treatment and prevention of age-related disease." [study done on UM-HET3, a heterogeneous wild-type mouse].

Nothing like this had ever been seen before.

In Miller et al., 2014, using same UM-HET3 strain of mice and increasing dose of rapamycin 3 fold and starting at 9 months, there was increase lifespan 23% in male mice and 26% in female mice. (10)

Two leading research groups in Texas, (the Salvatore Oddo group and the Veronica Galvan) studying AD immediately sought to answer the question: 

Would inhibition of the mTOR pathway with rapamycin delay or prevent age-associated disease such as AD.

Following the Harrison study in 2009 showing that rapamycin administered to middle age mice increased their lifespan, their was great interest in use of rapamycin on mouse models of A.D.

 The first published study in 2010 was by the Veronica Galvan group.

"Inhibition of mTOR by Rapamycin Abolishes Cognitive Deficits and Reduces Amyloid-B Levels in a Mouse Model of Alzheimer's Disease", Patricia Spilman, Arlan Richardson, Veronica Galvan, 2010. (3)

Conclusion: "Our data suggest that inhibition of mTOR by rapamycin, an intervention that extends lifespan in mice, can slow or block AD progression in a transgenic mouse model of the disease. Rapamycin, already used in clinical settings, may be a potentially effective therapeutic agent for the treatment of AD."

Findings:

Rapamycin abrogates memory deficits in AD mice.

Rapamycin inhibits mTOR and decreases AB(42) levels in brains of AD mice.

Rapamycin increases autophagy in brains of AD mice.

Rapamycin was started at 4 months of age and administered for 13 weeks and mice were tested at 7 month-old.

The mice used were PDAPP, a transgenic mouse model for AD with human AD genes implanted. 

The dose of rapamycin was 2.24 mg/kg, same dose used by Harrison for lifespan extension.

At end of experiment, untreated mice had significant deficits.  The rapamycin treated AD mice were indistinguishable from non-AD littermates.

They stated in discussion: "The data presented here, to our knowledge, the first to show that inhibition of mTOR by rapamycin decreased AB42 levels and restored cognitive function in a mouse model of AD. Our data suggests that the reduction in AB42 levels and the improvement in cognitive function in rapamycin treated AD mice may be consequence of the induction of autophagy in hippocampus. 

"Molecular Interplay between mTOR, Amyloid-B and Tau", Caccamo, Majumder, Arlan Richardson, Salvatore Oddo, 2010. (4)

The conclusion was: "In summary, we provide compelling evidence showing an interrelationship between mTOR signaling and AD-like neuropathology in AD mice. Specifically, our data point toward mTOR as a molecular link between AB accumulation and cognitive dysfunction. Finally, we show that rapamycin, in addition to extending life span ameliorates the AD-like pathology in AD mice."

6 month old AD mice were fed rapamycin for 10 weeks. The mice used were 3xTg-AD and had human gene APP-Swe and human Tau gene. APP is precursor protein of AB.

The dose of rapamycin used was same used by Harrison in 2009 life extension study.

Results: 

Accumulation of AB increases mTOR signaling in cell culture.

Rapamycin reduces AB levels in cell culture.

mTOR signaling is increased in cortex and hippocampus of AD mice.

Rapamycin rescues early learning and memory deficits in AD mice.

Rapamycin lowers mTOR activity to normal (wild-type mice) levels and rescues AB and Tau pathology.

Rapamycin reduces AB(42) levels and deposition in brain.

Rapamycin administration significantly decreases Tau pathology.

Rapamycin increases autophagy induction.

Autophagy mediates the rapamycin effects on AB and Tau pathology.

Autophagy is necessary for the rapamycin-mediated decrease in AB levels.

Abstract: "Using an animal model of AD, we show that pharmacologically restoring mTOR signaling [reducing to wild-type levels] with rapamycin rescues cognitive deficits and ameliorates AB and Tau pathology by increasing autophagy. Indeed, we further show that autophagy induction is necessary for the rapamycin -mediated reduction in AB levels. The results presented here provide a molecular basis for the AB-induced cognitive deficits an moreover, show that rapamycin, an FDA approved drug, improves learning and memory and reduces AB and Tau pathology."

Discussion: "In summary, we provide compelling evidence showing an interrelationship between mTOR signaling and AD-like neuropathology in 3xTg-AD mice. Specifically, our data point toward mTOR as molecular link between AB accumulation and cognitive dysfunction. Finally, we show that rapamycin, in addition to extending life span ameliorates the AD-like pathology in 3xTg-AD mice."

Based upon these two excellent studies, it was know in  2010 that rapamycin, an FDA approved drug, had great potential to prevent AD in humans and human clinical trials were indicated.

"Inducing Autophagy by Rapamycin BEFORE, but NOT AFTER, the formation of Plaques and Tangles Ameliorates Cognitive Deficits." Majumder, Arlan Richardson, Salvatore Oddo, 2011. (5)

In this study, Oddo group used same type AD mouse model as in previous study and administered rapamycin in same dose.

In one group of mice rapamycin was started at 2 months of age and administered for 15 months, called AD(2-18) mice. The second group of mice rapamycin was started at 15 months of age and administered for 3 months, called AD(15-18) mice.

Results: In the AD(2-18) mice, rapamycin reduces AB plaques and neurofibrillary tangles. 

No change from controls in AD(15-18) mice.

Life long administration of rapamycin AD(2-18) mice reduced AB40 and AB42 @ 50%. In AD(15-18) mice no change from controls.

"In summary, Rapamycin reduces soluble AB and insoluble AB plaques if started at 2 months; but did not reduce soluble AB or insoluble plaques when started at 15 months AFTER PLAQUES WERE WIDELY ESTABLISHED."

"In regard to Tau, Rapamycin started at 2 months significantly reduced Tau. Rapamycin started at 15 months had no effect on Tau."

"Rapamycin reduced microglia activation when started at 2 months; but had no effect on activated microglia when started at 15 months". 

Interestingly, rapamycin decreased TOR signaling when started at both 2 months and 15 months.

Rapamycin induces increase in AUTOPHAGY when started at both 2 and 15 months. However, when rapamycin started at 15 months, decrease in TOR signaling and increase in autophagy, did not ameliorate AD phenotype.

Abstract: "Here we show that rapamycin, when given prophylactically to 2-month-old AD mice throughout their lives, induces autophagy and significantly reduces plaque and tangles and cognitive deficits. In contrast, inducing autophagy in 15-month-old, which have established plaques and tangles, has NO EFFECTS on AD-like pathology and cognitive deficits."

"In conclusion, we show that autophagy induction via rapamycin MAY REPRESENT A VALID THERAPEUTIC STRATEGY IN AD WHEN ADMINISTERED EARLY IN DISEASE PROGRESSION". "Because of ts anti-aging properties and effects on clearing protein deposits, rapamycin should be considered in future clinical trials for age dependent neurodegenerative disorders."

Rapamycin decreased mTOR when started at both 2 months old and 15 month old mice and increased autophagy in both groups of mice. However, there was dissociated between increasing autophagy and AB clearance in 15 month old mice. The problem is that in late AD, autophagy fails. This has been confirmed in later studies.

Oddo writes in paper, "The role of mTOR signaling in Alzheimer disease", 2012

"At earlier stages of Abeta accumulation, induction of autophagy may facilitate its clearance. As the disease progresses, deficiencies in the clearance of autophagic vacuoles may occur and thus increasing autophagy may exacerbate the AD phenotype."

[See: Basic Science.Discussion of Autophagy in regard to AB]

In the 2011 study,  it was noted that microglia activation is an invariable feature of AD.  In the mice with Rapamycin started at 2 months of age, Rapamycin reduces microglia activation. In contrast,  when rapamycin started at 15 months, it had no effect on degree of microglia activation. They stated, "these results highlight a correlation between the reduction in fibrillar AB deposits and the number of activated microglia. Late started rapamycin did not reduce fibrillar deposits and did not reduce activated microglia.

These finding indicate rapamycin will not ameliorate late stage of AD with dementia and established plaques and tangles.

Alzheimer's Disease in APOE4 carriers has 4 clinical stages: Latent, Prodromal. MCI and Dementia.  Prior mouse studies showed prevention when started EARLY and no effect when started LATE. In this study, they start in the MIDDLE, at 7 months. The results were very good. These results suggest that in the Prodromal stage and perhaps even in early stage of MCI, rapamycin may rescue patients. Certainly this requires experience in humans; but there is hope. 

"Chronic rapamycin restores brain vascular integrity and function through NO synthase activation and improves memory in symptomatic mice modeling Alzheimer's disease", Ai-ling Lin, Arlan Richardson, Veronica Galvan, et.al. 2013.(6)

The study uses transgenic AD mice. The mice are described as hAPP(J20). The  hAPP transgene carries the Swedish and Indiana familial AD mutation. 

Rapamycin is started at 7 months of age. This is after the onset of robust AD-like deficits that affect spatial learning and memory. The mice were then treated with rapamycin for 4 months and then tested at 11 months.

Results:

Improved memory: Rapamycin treatment started after onset AD-like cognitive deficits ameliorated spatial learning in symptomatic mice. 

Restored cerebral blood flow: Using MRI imaging showed cerebral blood flow restored to indistingishable from normal litter mates.

Increased vascular density: The control AD mice had pronounced reduction in cerebral vessel density which was completely abrogated in rapamycin treated AD mice. 

Reduced cerebrovascular amyloid angiopathy (CAA) and AB plaques. Reduction in CAA stopped microhemorrhages and hemosiderin deposits in brain.

Rapamycin induced Nitric Oxide Synthase activity for restoration of cerebral blood flow. Mechanism of action was TOR blocked Nitric oxide synthase action (NOS). Rapamycin blocked this effect of TOR, restored NOS activity. The action of rapamycin thus caused endothelial cells to release Nitric oxide which caused vasodilation.

The abstract states: "chronic reduction of TOR activity by rapamycin started after disease onset restored cerebral blood flow, and brain vascular density, reduced cerebral amyloid angiopathy and microhemorrhages, decreased amyloid burden and improved cognitive function in symptomatic AD mice. "

"Rapamycin treatment induced activation of endothelial nitric oxide synthase and NO release in brain endothelium...Rapamycin preserves vascular density and cerebral blood flow in AD mouse brains through NOS activation."

"Taken together, our data suggests that chronic reduction of TOR activity by rapamycin blocked the progression of AD-like cognitive and histopathologic deficits by preserving vascular integrity and function. Drugs that inhibit TOR pathway may have promise as a therapy for AD".

Discussion: "In summary, our data indicate that chronic inhibition of mTOR by rapamycin, an intervention that extends lifespan in mice, negates vascular breakdown through activation of NOS, likely eNOS (endothelial cell produced NOS) in brain vascular endothelium and improves cognitive function when administered after onset of AD-like deficits in transgenic mice modeling the disease. Although rapamycin or rapamycin analogs have side effects that are undesirable in the elderly, it is possible that therapies in which the drug is us in "on-off" schedules may be devised for the treatment of early or moderate AD."

Note: The schedule we use is intermittent; one day ON and 6 days OFF.

The comment about undesirable side effects refers to use of rapamycin as approved for daily use in transplant medicine; a comment I completely agree endorse.

The very important things was suggestion that rapamycin could be used for "early or moderate AD"; a clinical stage I take to mean MCI (mild cognitive impairment).

2013, MOUSE STUDY,  ODDO group, TAUOPATHIES, Rapamycin.

"mTOR Regulates Tau Phosphorylation and Degradaton: Implications for Alzheimer's Disease and Other Tauopathies. Caccamo..Oddo, 2013.(7)

In this study they used a mouse model that expressed mutant human tau. They reduced mTOR signaling with rapamycin and ameliorated tau pathology. This is extremely important paper related to mTOR, Tau and reduction of mTOR with rapamycin. It is considered in "Basic Science" section in area which looks at TAU. 

It is also another Mouse, AD, rapamycin study; but mainly study about mTOR and Tau.

"Genetic Reduction of Mammalian Target of Rapamycin Ameliorates Alzheimer's Disease-Like Cognitive and Pathological Deficits by Restoring Hippocampal Gene Expression Signature." Caccamo, ...Oddo, 2014 (8)

This study used the same type AD mice used by Oddo group in prior study; however, mice were modified by removing one copy of the mTOR gene. The results were similar to treatment with rapamycin. 

Abstract:

"Elevated mammalian target of rapamycin (mTOR) signaling has been found in Alzheimer's disease (AD) patients and is linked to diabetes and aging, two known risk factors for AD...Here, we genetically reduced mTOR signaling in the brains of Tg2576 mice, a widely used animal model of AD. We found that suppression of mTOR signaling reduced amyloid-B deposits and rescued memory deficits. Mechanistically, the reduction in mTOR signaling led to an increase in autophagy induction and restored the hippocampal gene expression of the Tg2576 mice to wild-type levels. Our results implicate hyperactive mTOR signaling as a previous unidentified signaling pathway underlying gene-expression dysregulation and cognitive deficits in AD. Furthermore, hyperactive mTOR signaling may represent a molecular pathway by which aging contributes to the development of AD."

Conclusion: "To summarize, we provide compelling evidence clearly indicating a primary role of mTOR in AD pathogenesis and suggest a possible way by which aging increases the development of this disorder. Further, the data presented here point to mTOR as a potential therapeutic target for this disorder. The clinical implication of these finding is profound as there are several known compounds, some FDA-approved, known to reduce mTOR signaling." 

Taken together, the results of these 6 mouse studies are extraordinary. In next section we look at mice which are genetically modified to have human APOE4 gene.