Discovery, synthesis and exploration of N-benzylsulfonyl-2-phenylazepanes as inhibitors of Bim expression in a mouse embryonic fibroblast model.

Chronic activation of beta-adrenergic receptors by the sympathetic nervous system results in the apoptosis of cardiomyocytes. Due to the inability of cardiomyocytes to regenerate, this can result in heart failure. Upregulation of the pro-apoptotic protein Bim has been implicated as the cause of cardiomyocyte apoptosis. Beta blockers are the frontline drug used to negate this apoptotic pathway, as no direct inhibitors of Bim expression currently exist. Unfortunately, treatment of heart failure using beta blockers is not optimal. Therefore, direct inhibition of Bim expression is an attractive strategy to provide protection against stress-induced apoptosis of cardiomyocytes. Herein we explore a class of N-benzylsulfonyl-2-phenylazepanes to obtain anti-apoptotic compounds capable of reducing Bim expression levels to 7% of the control at 10 µM in cardiomyocytes under conditions of chronic beta-adrenergic receptor activation with little inhibitory effect upon protein kinase A activity and minimal toxicity.

Bim Deletion Reduces Functional Deficits Following Ischemic Stroke in Association with Modulation of Apoptosis and Inflammation.

Cellular apoptosis is a key pathological mechanism contributing to neuronal death following ischemic stroke. The pro-apoptotic Bcl-2 family protein, Bim, is an important regulator of apoptosis. In this study we investigated the effect of Bim expression on post-stroke functional outcomes, brain injury and inflammatory mechanisms. Wild type (WT) and Bim-deficient mice underwent 1-h middle cerebral artery occlusion (MCAO) followed by 23 h of reperfusion. At 24-h post-stroke, we assessed functional deficit, infarct volume, immune cell death, as well as the number of infiltrating immune cells in the brain and circulating immune cells. Bim deficiency did not affect infarct volume (P > 0.05), but resulted in less motor impairment (~ threefold greater latency to fall in hanging grip strength test, P < 0.05) and a lower median clinical score than WT mice (P < 0.05). Additionally following MCAO, Bim-deficient mice exhibited fewer myeloid cells (particularly neutrophils) in the ischemic brain hemisphere and less apoptosis of CD3+ T cells in the spleen and thymus compared with WT (all P < 0.05). After MCAO, Bim-deficient mice also tended to have more M2-polarised macrophages in the brain than WT mice. In sham-operated mice, we found that Bim deficiency resulted in greater numbers of circulating total CD45+ leukocytes, Ly6Clo+ monocytes and CD3+ T cells, although MCAO did not affect the number of circulating cells at 24 h in either genotype. Our findings suggest that Bim deficiency modulates post-stroke outcomes, including reductions in motor impairment, brain inflammation and systemic post-stroke leukocyte apoptosis. Bim could therefore serve as a potential therapeutic target for stroke.

DR5 and caspase-8 are dispensable in ER stress-induced apoptosis.

The endoplasmic reticulum (ER) stress response constitutes cellular reactions triggered by a wide variety of stimuli that disturb folding of proteins, often leading to apoptosis. ER stress-induced apoptotic cell death is thought to be an important contributor to many human pathological conditions. The molecular mechanism of this apoptosis process has been highly controversial with both the receptor and the mitochondrial pathways being implicated. Using knockout mouse models and RNAi-mediated gene silencing in cell lines, our group and others had demonstrated the importance of the mitochondrial apoptotic pathway in ER stress-induced cell death, particularly the role of the pro-apoptotic BH3-only BCL-2 family members, BIM and PUMA. However, a recent report suggested a central role for the death receptor, DR5, activated in a ligand-independent manner, and the initiator caspase, caspase-8, in ER stress-induced cell death. This prompted us to re-visit our previous observations and attempt to reproduce the newly published findings. Here we report that the mitochondrial apoptotic pathway, activated by BH3-only proteins, is essential for ER stress-induced cell death and that, in contrast to the previous report, DR5 as well as caspase-8 are not required for this process.

BH3-only proteins: a 20-year stock-take.

BH3-only proteins are the sentinels of cellular stress, and their activation commits cells to apoptosis. Since the discovery of the first BH3-only protein BAD almost 20 years ago, at least seven more BH3-only proteins have been identified in mammals. They are regulated by a variety of environmental stimuli or by developmental cues, and play a crucial role in cellular homeostasis. Some are considered to be tumor suppressors, and also play a significant role in other pathologies. Their non-apoptotic functions are controversial, but there is broad consensus emerging regarding their role in apoptosis, which may help in designing better therapeutic agents for treating a variety of human diseases.