Channels, Transporters, and Receptors at Membrane Contact Sites.

Membrane contact sites (MCSs) are specialized regions where two or more organelle membranes come into close apposition, typically separated by only 10-30 nm, while remaining distinct and unfused. These sites play crucial roles in cellular homeostasis, signaling, and metabolism. This review focuses on ion channels, transporters, and receptors localized to MCSs, with particular emphasis on those associated with the plasma membrane and endoplasmic reticulum (ER).

α1 S1928 Phosphorylation of Ca1.2 Channel Controls Vascular Reactivity and Blood Pressure.

Background: Increased vascular Ca1.2 channel function causes enhanced arterial tone during hypertension. This is mediated by elevations in angiotensin II/protein kinase C signaling.

Atomistic mechanisms of the regulation of small-conductance Ca-activated K channel (SK2) by PIP2.

Small-conductance Ca-activated K channels (SK, K2) are gated solely by intracellular microdomain Ca. The channel has emerged as a therapeutic target for cardiac arrhythmias. Calmodulin (CaM) interacts with the CaM binding domain (CaMBD) of the SK channels, serving as the obligatory Ca sensor to gate the channels.

14-3-3 promotes sarcolemmal expression of cardiac Ca 1.2 and nucleates isoproterenol-triggered channel super-clustering.

Unlabelled: The L-type Ca channel (Ca 1.2) is essential for cardiac excitation-contraction coupling. To contribute to the inward Ca flux that drives Ca -induced-Ca -release, Ca 1.

Unraveling the Connection: Cholesterol, Calcium Signaling, and Neurodegeneration.

Cholesterol and calcium play crucial roles as integral structural components and functional signaling entities within the central nervous system. Disruption in cholesterol homeostasis has been linked to Alzheimer's, Parkinson's, and Huntington's Disease while alterations in calcium signaling is hypothesized to be a key substrate for neurodegeneration across many disorders. Despite the importance of regulated cholesterol and calcium homeostasis for brain health there has been an absence of research investigating the interdependence of these signaling molecules and how they can tune each other's abundance at membranes to influence membrane identity.

BIN1 knockdown rescues systolic dysfunction in aging male mouse hearts.

Cardiac dysfunction is a hallmark of aging in humans and mice. Here we report that a two-week treatment to restore youthful Bridging Integrator 1 (BIN1) levels in the hearts of 24-month-old mice rejuvenates cardiac function and substantially reverses the aging phenotype. Our data indicate that age-associated overexpression of BIN1 occurs alongside dysregulated endosomal recycling and disrupted trafficking of cardiac Ca1.

α-Synuclein-dependent increases in PIP5K1γ drive inositol signaling to promote neurotoxicity.

Anomalous aggregation of α-synuclein (α-Syn) is a pathological hallmark of many degenerative synucleinopathies including Lewy body dementia (LBD) and Parkinson's disease (PD). Despite its strong link to disease, the precise molecular mechanisms that link α-Syn aggregation to neurodegeneration have yet to be elucidated. Here, we find that elevated α-Syn leads to an increase in the plasma membrane (PM) phosphoinositide PI(4,5)P, which precipitates α-Syn aggregation and drives toxic increases in mitochondrial Ca and reactive oxygen species leading to neuronal death.

NPC1-dependent alterations in K2.1-Ca1.2 nanodomains drive neuronal death in models of Niemann-Pick Type C disease.

Lysosomes communicate through cholesterol transfer at endoplasmic reticulum (ER) contact sites. At these sites, the Niemann Pick C1 cholesterol transporter (NPC1) facilitates the removal of cholesterol from lysosomes, which is then transferred to the ER for distribution to other cell membranes. Mutations in NPC1 result in cholesterol buildup within lysosomes, leading to Niemann-Pick Type C (NPC) disease, a progressive and fatal neurodegenerative disorder.

Role of Lysosomal Cholesterol in Regulating PI(4,5)P-Dependent Ion Channel Function.

Lysosomes are central regulators of cellular growth and signaling. Once considered the acidic garbage can of the cell, their ever-expanding repertoire of functions include the regulation of cell growth, gene regulation, metabolic signaling, cell migration, and cell death. In this chapter, we detail how another of the lysosome's crucial roles, cholesterol transport, plays a vital role in the control of ion channel function and neuronal excitability through its ability to influence the abundance of the plasma membrane signaling lipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P).

Acute phosphatidylinositol 4,5 bisphosphate depletion destabilizes sarcolemmal expression of cardiac L-type Ca channel Ca1.2.

Ca1.2 channels are critical players in cardiac excitation-contraction coupling, yet we do not understand how they are affected by an important therapeutic target of heart failure drugs and regulator of blood pressure, angiotensin II. Signaling through G-coupled AT1 receptors, angiotensin II triggers a decrease in PIP, a phosphoinositide component of the plasma membrane (PM) and known regulator of many ion channels.

The E3 Ubiquitin Ligase CRL5 Regulates Dentate Gyrus Morphogenesis, Adult Neurogenesis, and Animal Behavior.

The dentate gyrus (DG) is an essential part of the hippocampal formation and participates in the majority of hippocampal functions. The DG is also one of the few structures in the mammalian central nervous system that produces adult-born neurons and, in humans, alterations in adult neurogenesis are associated with stress and depression. Given the importance of DG in hippocampal function, it is imperative to understand the molecular mechanisms driving DG development and homeostasis.

Biophysical physiology of phosphoinositide rapid dynamics and regulation in living cells.

Phosphoinositide membrane lipids are ubiquitous low-abundance signaling molecules. They direct many physiological processes that involve ion channels, membrane identification, fusion of membrane vesicles, and vesicular endocytosis. Pools of these lipids are continually broken down and refilled in living cells, and the rates of some of these reactions are strongly accelerated by physiological stimuli.

Phosphoinositide transport and metabolism at membrane contact sites.

Phosphoinositides are a family of signaling lipids that play a profound role in regulating protein function at the membrane-cytosol interface of all cellular membranes. Underscoring their importance, mutations or alterations in phosphoinositide metabolizing enzymes lead to host of developmental, neurodegenerative, and metabolic disorders that are devastating for human health. In addition to lipid enzymes, phosphoinositide metabolism is regulated and controlled at membrane contact sites (MCS).

IPR-driven increases in mitochondrial Ca promote neuronal death in NPC disease.

Ca is the most ubiquitous second messenger in neurons whose spatial and temporal elevations are tightly controlled to initiate and orchestrate diverse intracellular signaling cascades. Numerous neuropathologies result from mutations or alterations in Ca handling proteins; thus, elucidating molecular pathways that shape Ca signaling is imperative. Here, we report that loss-of-function, knockout, or neurodegenerative disease-causing mutations in the lysosomal cholesterol transporter, Niemann-Pick Type C1 (NPC1), initiate a damaging signaling cascade that alters the expression and nanoscale distribution of IPR type 1 (IPR1) in endoplasmic reticulum membranes.

NPC1 regulates the distribution of phosphatidylinositol 4-kinases at Golgi and lysosomal membranes.

Cholesterol and phosphoinositides (PI) are two critically important lipids that are found in cellular membranes and dysregulated in many disorders. Therefore, uncovering molecular pathways connecting these essential lipids may offer new therapeutic insights. We report that loss of function of lysosomal Niemann-Pick Type C1 (NPC1) cholesterol transporter, which leads to neurodegenerative NPC disease, initiates a signaling cascade that alters the cholesterol/phosphatidylinositol 4-phosphate (PtdIns4P) countertransport cycle between Golgi-endoplasmic reticulum (ER), as well as lysosome-ER membrane contact sites (MCS).

β-Adrenergic control of sarcolemmal Ca1.2 abundance by small GTPase Rab proteins.

The number and activity of Ca1.2 channels in the cardiomyocyte sarcolemma tunes the magnitude of Ca-induced Ca release and myocardial contraction. β-Adrenergic receptor () activation stimulates sarcolemmal insertion of Ca1.

AKAP5 complex facilitates purinergic modulation of vascular L-type Ca channel Ca1.2.

The L-type Ca channel Ca1.2 is essential for arterial myocyte excitability, gene expression and contraction. Elevations in extracellular glucose (hyperglycemia) potentiate vascular L-type Ca channel via PKA, but the underlying mechanisms are unclear.

Sensing of nutrients by CPT1C controls SAC1 activity to regulate AMPA receptor trafficking.

Carnitine palmitoyltransferase 1C (CPT1C) is a sensor of malonyl-CoA and is located in the ER of neurons. AMPA receptors (AMPARs) mediate fast excitatory neurotransmission in the brain and play a key role in synaptic plasticity. In the present study, we demonstrate across different metabolic stress conditions that modulate malonyl-CoA levels in cortical neurons that CPT1C regulates the trafficking of the major AMPAR subunit, GluA1, through the phosphatidyl-inositol-4-phosphate (PI(4)P) phosphatase SAC1.

An anthrone-based Kv7.2/7.3 channel blocker with improved properties for the investigation of psychiatric and neurodegenerative disorders.

A set of novel Kv7.2/7.3 (KCNQ2/3) channel blockers was synthesized to address several liabilities of the known compounds XE991 (metabolic instability and CYP inhibition) and the clinical compound DMP 543 (acid instability, insolubility, and lipophilicity).

Disease-associated mutations in Niemann-Pick type C1 alter ER calcium signaling and neuronal plasticity.

Niemann-Pick type C1 (NPC1) protein is essential for the transport of externally derived cholesterol from lysosomes to other organelles. Deficiency of NPC1 underlies the progressive NPC1 neurodegenerative disorder. Currently, there are no curative therapies for this fatal disease.

Neuronal ER-plasma membrane junctions organized by Kv2-VAP pairing recruit Nir proteins and affect phosphoinositide homeostasis.

The association of plasma membrane (PM)-localized voltage-gated potassium (Kv2) channels with endoplasmic reticulum (ER)-localized vesicle-associated membrane protein-associated proteins VAPA and VAPB defines ER-PM junctions in mammalian brain neurons. Here, we used proteomics to identify proteins associated with Kv2/VAP-containing ER-PM junctions. We found that the VAP-interacting membrane-associated phosphatidylinositol (PtdIns) transfer proteins PYK2 N-terminal domain-interacting receptor 2 (Nir2) and Nir3 specifically associate with Kv2.

Niemann-Pick Type C Disease Reveals a Link between Lysosomal Cholesterol and PtdIns(4,5)P That Regulates Neuronal Excitability.

There is increasing evidence that the lysosome is involved in the pathogenesis of a variety of neurodegenerative disorders. Thus, mechanisms that link lysosome dysfunction to the disruption of neuronal homeostasis offer opportunities to understand the molecular underpinnings of neurodegeneration and potentially identify specific therapeutic targets. Here, using a monogenic neurodegenerative disorder, NPC1 disease, we demonstrate that reduced cholesterol efflux from lysosomes aberrantly modifies neuronal firing patterns.

β-adrenergic-mediated dynamic augmentation of sarcolemmal Ca 1.2 clustering and co-operativity in ventricular myocytes.

Key Points: Prevailing dogma holds that activation of the β-adrenergic receptor/cAMP/protein kinase A signalling pathway leads to enhanced L-type Ca 1.2 channel activity, resulting in increased Ca influx into ventricular myocytes and a positive inotropic response. However, the full mechanistic and molecular details underlying this phenomenon are incompletely understood.