This year’s Nobel Prize for Physiology or Medicine was awarded for work elucidating circadian rhythm molecular pathways. Greater understanding of circadian rhythm and its implications bring with it exciting discoveries. A role for circadian rhythm in ischemic cardiac protection has been identified in several studies

• The incidence of myocardial infarction (Ml) is known to be higher in the morning1 and there is a higher

rate of greater ischemic injury when the Ml occurs in the early morning2 . Additionally, the light elicited, circadian rhythm protein Per2, has been shown to have a cardioprotective role in ischemic cardiac events3 .

The cardiac metabolic response to ischemia is the source of tremendous damage to heart tissue. A lack of oxygen during cardiac ischemia, disrupts aerobic, oxidative phosphorylation resulting in an ATP deficit that leads to cell death. Products of glycolysis are shifted away  from  oxidative  phosphorylation to the production of lactate – this shift results in damaging acidosis and less efficient ATP production. Studies on cardiac metabolism have found a key role for light induced expression  increase of Per2  in  the transcriptional induction of glycolytic enzymes, enhancing oxygen efficient glycolysis, making the heart better prepared to adapt to ischemia.4• 5 .

In a recent study, Dr. Colleen M. Bartman and her colleagues set out to clarify how PER2 exerts its cardioprotective effects on oxygen efficient pathways, to identify new therapeutic targets. To identify PER2- dependent miRNA elements of cardioprotective pathways, QIAGEN RF Kits were used to  isolate  miRNA from wildtype and PER2^-/- mice and compare expression in miRNA PCR arrays. Of the 352 most abundantly expressed PER2-dependent miRNAs, miR-21 stood out.

To confirm miR-21 as a downstream PER2 target, wildtype and PER^-/- mice were exposed to cardioprotective ischemic preconditioning (IPC – 4 cycles of 5 min. ischemia/5 min reperfusion) and heart miR-21 expression was analyzed via qPCR using QIAGEN miSCRIPT miRNA probes. IPC resulted in a 2.4- fold induction of miR-21 in wildtype mice,  with  no  upregulation  observed  in Per2^-/-mice.  The group  was then able to show an increase in miR-21 and PER2 with exposure to light. Exposing wildtype mice to

l4h/day of intense light increased cardiac miR-21 levels 6-fold and PER2 levels 4-fold.  Next, wildtype controls or miR-21^-/- mice were exposed to 3 hours of intense light prior to myocardial ischemia and reperfusion injury. Light exposure significantly reduced infarct sizes in wildtype controls but failed to induce cardioprotection in miR-21^-/- mice. These finding suggests that miR-21  is a downstream  target of light / PER2 in exerting cardioprotective effects.

In humans, one week of intense light exposure in 8 human subjects increased  their blood plasma  miR-21 levels 3.5-fold and phosphofructokinase (PFK) activity increased 49%. PFK expression was monitored as it is the key regulatory enzyme in the glycolytic pathway. The significant increase in PFK  activity indicates  miR- 21’s cardioprotective effects could come from enhancement of glycolysis.

1. Muller JE, Stone PH, Turi ZG, Rutherford JD, Czeisler CA, Parker C, et al. Circadian variation in the frequency of onset of acute myocardial infarction. N Engl J Med. 1985;313(21):1315–22
2. Reiter R, Swingen C, Moore L, Henry TD, Traverse JH (2012) Circadian dependence of infarct size and left ventricular function after ST elevation myocardial infarction. Circ Res 110: 105–110
3. Suarez‐Barrientos et al (2011) Circadian variations of infarct size in acute myocardial infarction. Heart 97: 970–976
4. Gary D.Lopaschuk, Jagdip S. Jaswal (2012) A Role for Period 2 in Cardioprotection. Cell Met 16: 2-4
5. Tobias Eckel et al (2012) Adora2b-elicited Per2 stabilization promotes a HIF-dependent metabolic switch crucial for myocardial adaptation to ischemia. Nature Medicine 18, 774–782

Diabetes mellitus is one of the most common chronic diseases, globally. The prevalence has risen from 4.7% of adults over 18 years of age in 1980 to 8.5% in 2014¹. Plagued by treatment non-compliance, it is estimated that approximately 50% of Type 2 Diabetics fail to achieve adequate glycemic control². The positive association between diabetes and Alzheimer’s disease is well known – A large population-based study from Rotterdam suggested that diabetes can almost double the risk of developing Alzheimer’s disease and vascular dementia.³ The link, however between the metabolic disorder and the devastating neurological disease has remained the object of speculation.

Alzheimer’s disease (AD) is characterized by two types of brain lesions – extracellular β-amyloid (Aβ) accumulation in amyloid plaques and intracellular aggregation of hyperphosphorylated tau into neurofibrillary tangles⁴. A study detailed in Nature Scientific Reports, investigated the effect of high glucose on β-site amyloid precursor protein cleaving enzyme 1 (BACE1) expression and amyloidogenesis in vivo. BACE1 is the enzyme responsible for initiating β-amyloid (Aβ) generation from amyloid precursor protein (APP). Amyloid deposition begins 10-20 years before Alzheimer’s dementia onset, suggesting an early role in pathogenesis for Aβ accumulation; making BACE1 a desirable target of study⁵.

In their study, Dr. Ho Jae Han and his team showed an increase in Aβ deposition in diabetic, ZDF rat brains, in response to high glucose. ZDF rats were also shown to have higher levels of BACE1 expressions than those in lean control, ZLC rats. To provide a compelling link between diabetes and AD, the mechanism by which high glucose levels affected APP processing was investigated using mouse hippocampal neuron and SK-N-MC cells.

Using the QIAGEN QuantiNova SYBR Green PCR Kit the group was able to demonstrate via real-time PCR gene expression analysis that high glucose conditions increases expression of BACE1 through upregulation of HIF-1α expression. LXRα/ABCA1 were also upregulated in the presence of high glucose and shown to stimulate BACE1 by recruiting it to lipid rafts, where APP cleavage to Aβ occurs.

Further studies and proof that uncontrolled diabetes can lead to serious neurological impairment could spur early diagnosis programs and go a long way towards improved compliance with diabetes treatments. This would have a profound effect not only on the diabetes morbidity and mortality rate², but also on the prevalence of Alzheimer’s disease – having the potential to reduce Alzheimer’s incidence by up to 40%.

You can read more about this study in Nature Scientific Reports here. Explore our Alzheimer’s pathway to build and present your own findings of molecular interactions or visit our online Research Center and advance your understanding in Alzheimer’s disease and neurodegenerative diseases.

1. Global Report on Diabetes 2016. Geneva: World Health Organization
2. Luis-Emilio García-Pérez et. al. Adherence to Therapies in Patients with Type 2 Diabetes. Diabetes Ther. 2013 Dec; 4(2): 175–194.
3. Ott A. et al.: Diabetes mellitus and the risk of dementia: The Rotterdam study. Neurology 1999 10: 1937–1942.
4. Hardy J, Selkoe DJ: The amyloid hypothesis of Alzheimer’s disease: progress and problems on the road to therapeutics. Science 2002, 297: 353-356.
5. T. Ohara, Y. Doi, T. Ninomiya, et al. Glucose tolerance status and risk of dementia in the community. The Hisayama Study. Neurology 2011, 77:1126Hardy J, Selkoe DJ: The amyloid hypothesis of Alzheimer’s disease: progress and problems on the road to therapeutics. Science 2002, 297: 353-356.