Mitochondrial dysfunction regulates the JAK-STAT pathway via LKB1-mediated AMPK activation ER-stress-independent manner

Mitochondria affect cellular functions alone or in cooperation with other cellular organelles. Recent research has demonstrated the close relationship of mitochondria with the endoplasmic reticulum (ER), both at the physical and the functional level. In an effort to define the combined effect of mitochondrial dysfunction (MD) and ER stress in the proinflammatory activities of macrophages, the human macrophage-like monocytic leukemia cell line THP-1 was treated with mitochondrial electron transport chain (ETC) blockers, and changes in the cellular responses upon stimulation by interferon (IFN)-γ were analyzed. Inducing mitochondrial dysfunction (MD) with ETC blockers resulted in suppression of IFN-induced activation of JAK1 and STAT1/3, as well as the expression of STAT1-regulated genes. In addition, experiments utilizing pharmacological modulators of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and liver kinase B1 (LKB1)-deficient HeLa cells demonstrated that these suppressive effects are mediated by the LKB1-AMPK pathway. Treatment with pharmacological inhibitors of ER stress sensors failed to affect these processes, thus indicating that involvement of ER stress is not required. These results indicate that MD, induced by blocking the ETC, affects IFN-induced activation of JAK-STAT and associated inflammatory changes in THP-1 cells through the LKB1-AMPK pathway independently of ER stress.

The effect of calcitriol on endoplasmic reticulum stress response

Calcitriol, the active form of vitamin D, is known for its anticancer properties including induction of apoptosis, inhibition of angiogenesis, and metastasis. Calcitriol also increases intracellular calcium triggering apoptosis in a calpain-dependent manner. Since the main storage unit for cellular calcium is endoplasmic reticulum (ER) and a decrease in ER calcium levels might induce ER stress associated cell death, we hypothesized that the cellular actions of calcitriol occur via ER stress. We have evaluated induction of ER stress by assessing BIP expression and XBP-1 splicing in breast cancer cell lines (MCF-7 and MDA-MB-231) and mammary epithelial cell line MCF10A. Our results suggest that cytotoxic concentrations of calcitriol induce an ER stress related response indicated as increased BIP levels and XBP-1 splicing not only in breast cancer cells but also in mammary epithelial cell line. However, vehicle treatment also induced a similar response de-emphasizing the importance of such effect. Calcitriol also failed to activate calpains, further weakening the idea of ER stress as the main mechanism for apoptotic effects of calcitriol. Taken together our results suggest an association between ER stress and vitamin D signaling. However present data indicates that ER stress by itself is not sufficient to explain anticancer properties of calcitriol.

Endoplasmic reticulum and the microRNA environment in the cardiovascular system 1

Stress responses are important to human physiology and pathology, and the inability to adapt to cellular stress leads to cell death. To mitigate cellular stress and re-establish homeostasis, cells, including those in the cardiovascular system, activate stress coping response mechanisms. The endoplasmic reticulum, a component of the cellular reticular network in cardiac cells, mobilizes so-called endoplasmic reticulum stress coping responses, such as the unfolded protein response. MicroRNAs play an important part in the maintenance of cellular and tissue homeostasis, perform a central role in the biology of the cardiac myocyte, and are involved in pathological cardiac function and remodeling. In this paper, we review a link between endoplasmic reticulum homeostasis and microRNA with an emphasis on the impact on stress responses in the cardiovascular system.

Diabetic dyslipidemia: from evolving pathophysiological insight to emerging therapeutic targets

Diabetic dyslipidemia is characterized by hepatic very low density lipoprotein (VLDL) and intestinal chylomicron overproduction, reduced high density lipoprotein cholesterol (HDL-C) level, increased propensity of small dense LDL (sdLDL) and increased postprandial lipemia. This dyslipidemic profile is also strongly linked to other features of the metabolic syndrome. Diabetic dyslipidemia is a well-recognized risk factor for atherosclerotic cardiovascular diseases. Currently, statins remain the first line therapy primarily through reducing the atherogenic LDL. Clinical trials on other lipid modifying agents were met with variable success in selective patient populations. Emerging new insights into the pathophysiology of lipid metabolism, in general, and diabetic dyslipidemia, in particular, have opened up potentially novel therapeutic strategies to further reduce the risk associated with diabetic dyslipidemia and insulin resistant state.