BACE1 Knockout Mice and BACE1 inhibition in Mouse models of obesity/diabetes Stuart Irvine

Obesity & Type II Diabetes The problem In the uk, it is estimated that 60.8% of adults and 31.1% of children are overweight and around a quarter of the population categorised as obese. There is a long list of medical conditions associated with obesity, perhaps most importantly is type II diabetes, which can dramatically increase the chances of disease of the heart, vessels, kidneys, eyes, nervous system etc etc. One feature obese patients seem to show is reduced sensitivity to insulin and leptin hormones. Insulin is produced in the pancreas by beta-islet cells and is important primarily in regulating blood glucose levels. Type II diabetes occurs in obese individuals when cells are desensitised to insulin due to the prolonged high levels of blood glucose and circulating insulin. Leptin is an Adipose-derived hormone responsible for regulating satiety (hunger) and thus food intake, regulate, at least in part, an increase in energy expenditure via stimulation of the beta3 adrenoceptor and activation of uncoupling proteins, and seems to play a role in glucose metabolism via the POMC pathway. Because leptin is adipose-derived, the levels in the blood are largely proportionate to body fat. So in a similar story to insulin, patients with obesity have prolonged exposure to high levels of leptin and seem to be resistant to its effects. Controversially, the other side of the coin is that obese patients may be inherantly resistant to or deficient of leptin. Whether leptin resistance and deficiency is a cause or consequence (or both) of obesity is still being discussed. More recently, leptin deficiency has been linked to Alzheimer’s disease, via its regulation of glycogen synthase kinase 3 (GSK3) and its role in tau phosphorylation http://www.dh.gov.uk/health/2012/04/obesityfacts/

Leptin X Leptin is an adipose derived enzyme responsible for regulating appetite and energy expenditure. It’s main target is the hypothalamus, where it is thought to mediate the production of neuropeptide Y, melanocyte-stimulating hormone and corticotropin-releasing hormone. In a normal human, an increased amount of circulating leptin will result in decreased appetite, decreased food-intake and an increase in energy expenditure. In an obese human, because of prolonged high levels of circulating leptin, the leptin receptors become desensitized and its action is lost. Leptin was initially thought to be a candidate for treating obesity and type 2 diabetes, however this is only successful if the receptors will still respond to leptin. A new focus is to look at how we can modulate the leptin signalling pathways instead. From the following article: Leptin and the regulation of body weight in mammals Jeffrey M. Friedman and Jeffrey L. Halaas Nature 395, 763-770(22 October 1998)

Beta-secretase 1 (BACE1) and Mouse Models BACE1 is a protease responsible for cleaving Amyloid precursor protein (APP) into Aβ. Important in plaque formation in Alzheimer’s Disease It is known that patients with diabetes are at more risk of alzheimer’s as well as patients with alzheimers are at more risk of developing t2dm. BACE1 is well known for its role in Alzheimers disease, being responsible for cleaving Amyloid precursor protein into beta-amyloid, the primary component of beta-amyloid plaques that are one of the hallmarks of alzheimer’s disease. Professor Ashford and Dr Meakin have been looking at BACE1 ko mouse models and what happens when you try to induce obesity and type ii diabetes in these mice. They found that BACE1 ko models, when put on a high fat diet, were lean and insulin sensitive, unlike the WT controls. Similarly, they have found that WT mice on a high fat diet, after developing obesity and type ii dm, can revert back to a lean phenotype when BACE1 is inhibited. The weight lost is all adipose tissue, ie no muscle mass was lost. The possibility of BACE1 inhibitors, then, as a possible drug for obesity and diabetes is quite exciting, although the molecular mechanisms underlying their action is still not known. 1Biochem J. 2012 January 1; 441(Pt 1): 285–296. PMCID: PMC3242510 Reduction in BACE1 decreases body weight, protects against diet-induced obesity and enhances insulin sensitivity in mice Paul J. Meakin,*,1 Alex J. Harper,†,1,2 D. Lee Hamilton,* Jennifer Gallagher,* Alison D. McNeilly,‡ Laura A. Burgess,* Lobke M. Vaanholt,§ Kirsten A. Bannon,* Judy Latcham,† Ishrut Hussain,†,3 John R. Speakman,§ David R. Howlett,†,4 and Michael L.J. Ashford*,5 Using AstraZeneca compound AZ-20 and Merck 3 compounds (inhibitors of BACE1) in WT mice Those who have been on a high fat diet (obese and high leptin +/- diabetes) will revert to lean phenotype Weight lost is fat (muscle mass largely unchanged

BACE1 models and obesity BACE 1 KO model1 High fat diet Lean phenotype Low leptin levels in the blood Leptin sensitive/Low leptin levels Insulin sensitive (non-diabetic) BACE1 inhibition WT mice on a HF diet, with features of obesity, type II diabetes, leptin insensitivity etc Using BACE1 inhibitor, mice will revert back to lean, leptin/insulin-sensitive animal Weight lost is fat (not muscle) Leptin levels drop too 1P Meakin et al. Reduction in BACE1 decreases body weight, protects against diet-induced obesity and enhances insulin sensitivity in mice. Biochem J. 2012 January 1; 441(Pt 1): 285–296.

Objectives of my Project How is knocking out BACE1/ inhibiting BACE1 producing a lean animal, even on a high fat diet? Gene Expression Studies Fat Hypothalamus Muscle Leptin POMC UCP2 UCP1 AgRP UCP3 Β-3 Adrenoceptor NPY SOCS3 S OBOB mice no leptin (done, no mouse change) DB no functional leptin signalling (receptor mutation) (high leptin.- no repression) (merck3 done) Leptin levels and Leptin Action (UCPs- muscle and brown adipose) Sympathetic Nervous system (B-3 adrenoceptor) activity- (brown adipose) (Merck3 done) Hypothalamus gene expression (leptin action) Non-functioning leptin mice (DB mice/OBOB mice)