Statin-mediated reduction in mitochondrial cholesterol primes an anti-inflammatory response in macrophages by upregulating Jmjd3

Stains are known to be anti-inflammatory, but the mechanism remains poorly understood. Here we show that macrophages, either treated with statin in vitro or from statin-treated mice, have reduced cholesterol levels and higher expression of Jmjd3, a H3K27me3 demethylase. We provide evidence that lowering cholesterol levels in macrophages suppresses the ATP synthase in the inner mitochondrial membrane (IMM) and changes the proton gradient in the mitochondria. This activates NFkB and Jmjd3 expression to remove the repressive marker H3K27me3. Accordingly, the epigenome is altered by the cholesterol reduction. When subsequently challenged by the inflammatory stimulus LPS (M1), both macrophages treated with statins in vitro or isolated from statin-treated mice in vivo, express lower levels pro-inflammatory cytokines than controls, while augmenting anti-inflammatory Il10 expression. On the other hand, when macrophages are alternatively activated by IL4 (M2), statins promote the expression of Arg1, Ym1, and Mrc1. The enhanced expression is correlated with the statin-induced removal of H3K27me3 from these genes prior to activation. In addition, Jmjd3 and its demethylase activity are necessary for cholesterol to modulate both M1 and M2 activation. We conclude that upregulation of Jmjd3 is a key event for the anti-inflammatory function of statins on macrophages.

Statin-mediated reduction in mitochondrial cholesterol primes an anti-inflammatory response in macrophages by upregulating JMJD3

Stains are known to be anti-inflammatory, but the mechanism remains poorly understood. Here we show that macrophages, either treated with statin in vitro or from statin-treated mice, have reduced cholesterol levels and higher expression of Jmjd3, a H3K27me3 demethylase. We provide evidence that lowering cholesterol levels in macrophages suppresses the ATP synthase in the inner mitochondrial membrane (IMM) and changes the proton gradient in the mitochondria. This activates NFkB and Jmjd3 expression to remove the repressive marker H3K27me3. Accordingly, the epigenome is altered by the cholesterol reduction. When subsequently challenged by the inflammatory stimulus LPS (M1), both macrophages treated with statins in vitro or isolated from statin-treated mice in vivo, express lower levels pro-inflammatory cytokines than controls, while augmenting anti-inflammatory Il10 expression. On the other hand, when macrophages are alternatively activated by IL4 (M2), statins promote the expression of Arg1, Ym1, and Mrc1. The enhanced expression is correlated with the statin-induced removal of H3K27me3 from these genes prior to activation. In addition, Jmjd3 and its demethylase activity are necessary for cholesterol to modulate both M1 and M2 activation. We conclude that upregulation of Jmjd3 is a key event for the anti-inflammatory function of statins on macrophages.

mTOR complex 1 activity is required to maintain the canonical endocytic recycling pathway against lysosomal delivery

The plasma membrane of mammalian cells undergoes constitutive endocytosis, endocytic sorting, and recycling, which delivers nutrients to the lysosomes. The receptors, along with membrane lipids, are normally returned to the plasma membrane to sustain this action. It is not known, however, whether this process is influenced by metabolic conditions. Here we report that endocytic recycling requires active mechanistic target of rapamycin (aka mammalian target of rapamycin) (mTORC1), a master metabolic sensor. Upon mTORC1 inactivation, either by starvation or by inhibitor, recycling receptors and plasma membrane lipids, such as transferrin receptors and sphingomyelin, are delivered to the lysosomes. This lysosomal targeting is independent of canonical autophagy: both WT and Atg5^-/- mouse embryonic fibroblasts responded similarly. Furthermore, we identify hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), an endosomal sorting complexes required for transport (ESCORT-0) component, as a downstream target of mTORC1. Hrs requires mTORC1 activity to maintain its protein expression level. Silencing Hrs without decreasing mTORC1 activity is sufficient to target transferrin and sphingomyelin to the lysosomes. It is thus evident that the canonical recycling pathway is under the regulation of mTORC1 and likely most predominant in proliferating cells where mTORC1 is highly active.

Calmodulin-dependent activation and inactivation of anoctamin calcium-gated chloride channels

Calcium-dependent chloride channels serve critical functions in diverse biological systems. Driven by cellular calcium signals, the channels codetermine excitatory processes and promote solute transport. The anoctamin (ANO) family of membrane proteins encodes three calcium-activated chloride channels, named ANO 1 (also TMEM16A), ANO 2 (also TMEM16B), and ANO 6 (also TMEM16F). Here we examined how ANO 1 and ANO 2 interact with Ca²⁺/calmodulin using nonstationary current analysis during channel activation. We identified a putative calmodulin-binding domain in the N-terminal region of the channel proteins that is involved in channel activation. Binding studies with peptides indicated that this domain, a regulatory calmodulin-binding motif (RCBM), provides two distinct modes of interaction with Ca²⁺/calmodulin, one at submicromolar Ca²⁺ concentrations and one in the micromolar Ca²⁺ range. Functional, structural, and pharmacological data support the concept that calmodulin serves as a calcium sensor that is stably associated with the RCBM domain and regulates the activation of ANO 1 and ANO 2 channels. Moreover, the predominant splice variant of ANO 2 in the brain exhibits Ca²⁺/calmodulin-dependent inactivation, a loss of channel activity within 30 s. This property may curtail ANO 2 activity during persistent Ca²⁺ signals in neurons. Mutagenesis data indicated that the RCBM domain is also involved in ANO 2 inactivation, and that inactivation is suppressed in the retinal ANO 2 splice variant. These results advance the understanding of Ca²⁺ regulation in anoctamin Cl⁻ channels and its significance for the physiological function that anoctamin channels subserve in neurons and other cell types.

Targeted expression of anoctamin calcium-activated chloride channels in rod photoreceptor terminals of the rodent retina

PURPOSE

In the vertebrate retina, calcium-activated chloride channels are expressed in photoreceptor synaptic terminals. These channels are involved in the control of transmitter release in the dark. The search for their molecular identity has recently lead to the localization of the protein anoctamin 2 (also TMEM16B) in the outer plexiform layer of the rodent retina. Since both rod and cone photoreceptors have their terminals in this layer, it was not clear which of these express anoctamin 2. Here, we examine rod spherules and cone pedicles for expression of anoctamin 2.

METHODS

Expression of anoctamin genes was studied in the rat eye using RT-PCR. Immunohistochemical experiments were used to localize anoctamins and chloride transporters with their regulatory kinases. Photoreceptor synaptic proteins, as well as the lectins Peanut agglutinin and Griffonia simplicifolia agglutinin, were used to distinguish retinal structures.

RESULTS

Anoctamin 1, 2, and 10 were found to be expressed in the eye. Anoctamin 2 was expressed as a splice variant that includes exon 15 of the genomic structure. The protein is exclusively expressed in rod terminals and is not present in cone pedicles. Expression is not clustered at the ribbon complex, but spread across the presynaptic membrane where it colocalizes with the plasma membrane calcium pump. The electroneutral chloride transporter NKCC1 is expressed in photoreceptor terminals, together with its regulatory kinases SPAK and OSR1.

CONCLUSIONS

Rod photoreceptor terminals possess the molecular machinery for chloride accumulation and for the generation of calcium-dependent chloride currents conducted through anoctamin 2 channels. We discuss this finding in the framework of the established hypothesis that calcium-activated chloride channels are part of a feedback inhibition mechanism that limits transmitter release in the dark.

Expression patterns of anoctamin 1 and anoctamin 2 chloride channels in the mammalian nose

Calcium-activated chloride channels are expressed in chemosensory neurons of the nose and contribute to secretory processes and sensory signal transduction. These channels are thought to be members of the family of anoctamins (alternative name: TMEM16 proteins), which are opened by micromolar concentrations of intracellular Ca(2+). Two family members,ANO 1 (TMEM16A) and ANO 2 (TMEM16B), are expressed in the various sensory and respiratory tissues of the nose.We have examined the tissue specificity and sub-cellular localization of these channels in the nasal respiratory epithelium and in the five chemosensory organs of the nose: the main olfactory epithelium, the septal organ of Masera, the vomeronasal organ, the Grueneberg ganglion and the trigeminal system. We have found that the two channels show mutually exclusive expression patterns. ANO 1 is present in the apical membranes of various secretory epithelia in which it is co-localized with the water channel aquaporin 5. It has also been detected in acinar cells and duct cells of subepithelial glands and in the supporting cells of sensory epithelia. In contrast, ANO 2 expression is restricted to chemosensory neurons in which it has been detected in microvillar and ciliary surface structures. The different expression patterns of ANO 1 and ANO 2 have been observed in the olfactory, vomeronasal and respiratory epithelia. No expression has been detected in the Grueneberg ganglion or trigeminal sensory fibers. On the basis of this differential expression, we derive the main functional features of ANO 1 and ANO 2 chloride channels in the nose and suggest their significance for nasal physiology.