Name: imaging mitochondrial ca2+ uptake in astrocytes and neurons using genetically encoded ca2+ indicators (gecis)
Uploaded: 2022-01-22T14:00:00.000+00:00
Duration: 7 min 46 s
Description: Watch this Scientific Journal Video about Imaging Mitochondrial Ca2+ Uptake in Astrocytes and Neurons using Genetically Encoded Ca2+ Indicators GECIs at JoVE.com

This work was supported by the National Institute of Health National Institute of Neurological Disorders and Stroke (NINDS) grants R01NS069726 and R01NS094539 to SD. We thank Erica DeMers for the audio recording.

Procedures involving animals have been approved by the Institutional Animal Care and Use Committee (IACUC) at the University of Missouri-Columbia.
1. Construction of DNA plasmids
NOTE: For in vitro and in vivo imaging, DNA plasmids encoding GCaMP5G/6s with astrocyte- and neuron-specific promoters and mitochondrial targeting sequences are constructed.
<ol>
	<li>Insert mitochondrial matrix (MM)-targeting sequence (mito-) ATGT CCGTCCTGAC GCCGCTGCTG CTGCGGGGCT TGACAGGCTC GGCCCGGCGG CTCCCAGTGC CGCGCGCCAA GATCCATTCG TTG17 into the cloning sites EcoRI and BamHI in the backbone of adeno-associated virus (AAV) plasmid pZac2.1 to obtain plasmids containing astrocytic gfaABC1D promoter or neuronal CaMKII promoter18,19,20.</li>
	<li>Subclone GCaMP5G/6s into the cloning sites BamH I and Not 1 in the above plasmids to obtain new plasmids pZac-gfaABC1D-mito-GCaMP5G/6s and pZac-CaMKII-mito-GCaMP5G/6s that target transgene expression in mitochondria in astrocytes and neurons20,21 (Figure 1A).</li>
	<li>Prepare pZac-gfaABC1D-mito-GCaMP5G and pZac-CaMKII-mito-GCaMP6s DNA plasmids for transfection for in vitro study (Section 2). Produce AAV vectors with serotype 5 for astrocytes and serotype 9 for neurons for in vivo study18 (Section 3).</li>
</ol>
2. In vitro mitochondrial Ca2+ imaging in astrocytes and neurons
<ol>
	<li>Prepare primary astrocytes from the cortex of P1 neonatal mice and primary neurons from the cortex of E15-16 embryos18,22,23,24, and culture them on 12 mm diameter glass coverslips in 24-well plates using Dulbecco&#39;s Modified Eagle Medium (DMEM) containing 10% fetal bovine serum (FBS), and neuronal basal medium (NBM) containing 2% B27, respectively.</li>
	<li>Transfect mature astrocytes and neurons with pZac-gfaABC1D-GCaMP6s and pZac-CaMKII-GCaMP5G plasmids using lipid based transfection reagent to express GCaMP6s in the mitochondria of astrocytes and GCaMP5G in the mitochondria of neurons18,20,21. Transfect cells in each well with 0.5 &#181;g of DNA, and change the medium 6 h later. 
	NOTE: The astrocytes and neurons are ready for imaging 1-2 days after transfection.</li>
	<li>Perform in vitro mitochondrial Ca2+ imaging 1-2 days after transfection.
	<ol>
		<li>Transfer the glass coverslips cultured with astrocytes or neurons to the PH-1 perfusion chamber under an epifluorescence or two photon microscope.</li>
		<li>Stimulate astrocytic mitochondrial Ca2+ uptake with 100 &#956;M ATP in ACSF, or stimulate neuronal mitochondria with 100 &#956;M glutamate/10 &#956;M glycine20,25 (Figure 2 and Figure 3). 
		NOTE: Solution changes from ACSF to ATP- and glutamate/glycine-containing ACSF are controlled by an ALA-VM8 perfusion system21. The speed of the solution change is controlled at 1-2 mL/min by adjusting a valve.</li>
	</ol>
	</li>
</ol>
3. In vivo mitochondrial Ca2+ imaging in astrocytes and neurons
<ol>
	<li>AAV preparations.
	<ol>
		<li>Prepare the following recombinant adeno-associated virus (rAAV) vectors using the DNA plasmids prepared in section 1: rAAV2/5-gfaABC1D-mito-GCaMP5G and rAAV2/9-CaMKII-mito-GCaMP6s vectors. 
		NOTE: In this experiment, rAAV vectors of serotype 5 were prepared to express GCaMP5G in mitochondria in astrocytes and rAAV vectors of serotype 9 were prepared to express GCaMP6s in mitochondria in neurons.</li>
	</ol>
	</li>
	<li>Stereotaxic AAV injection.
	<ol>
		<li>Anesthetize the mouse with 3% isoflurane. 
		NOTE: Later during the surgery, the isoflurane levels are reduced to 2%.</li>
		<li>After the mouse reaches a surgical level of anesthesia, as determined by tail and toe pinch, shave the hair over the surgery site, motor or somatosensory cortex, with a hair trimmer.</li>
		<li>Position the mouse on the mouse stereotaxic device and fix the head with ear bars. Apply ophthalmic ointment to the eyes to protect them during the surgery. Use a heating pad to keep the body temperature of the mouse at 37 &#176;C throughout the surgery. 
		NOTE: Perform surgery using aseptic procedures. All surgical tools need to be sterilized either by autoclaving or a hot bead sterilizer.</li>
		<li>After the mouse is mounted on the stereotaxic device, sterilize the scalp with alternating iodine based scrub and 70% ethanol three times. Make an incision in the midline of the scalp to expose the injection site.</li>
		<li>Cut open the skin in the bregma-lamda axis and a create a ~1 mm diameter burr hole with a high speed drill at the intended injection location of the motor or somatosensory cortex.</li>
		<li>Use a 33 G Hamilton syringe containing adeno-associated virus (rAAV2/5-gfaABC1D-mito-GCaMP5G vectors [1 x 1011 GC] or rAAV2/9-CaMKII-mito-GCaMP6s vectors [1 x 1011 GC])&#160;to inject up to 1 &#181;L of virus at the target area. 
		NOTE: For example, for cortical viral delivery, inject the virus solution at two depths in multiple steps. First, insert the needle to a depth of 1 mm from the dura&#160;and allow 5 min for the brain to recover. Then, move the needle up to ~700 &#181;m depth and inject 500 nL of the virus solution at an injection speed of 10 nL/s using a hamilton syringe controlled by a microsyringe pump controller. After the injection is completed, wait for 5 min to allow the virus to diffuse into the brain. Then, move the needle up to the second injection location at a depth of 300 &#181;m. Here, inject an additional 500 nL of the virus solution. Wait for 10 min to allow the virus to diffuse into the brain.</li>
		<li>Close the scalp and the skin using a tissue adhesive. Let the mice recover on the heating pad. Send mice back to the animal facility after recovery.</li>
	</ol>
	</li>
	<li>Cranial-window intstallation and in vivo&#160;two-photon (2-P) imaging of mitochondrial Ca2+ signals. 
	NOTE: Cranial window implantation is done 3 weeks post AAV injection over the motor or somatosensory cortex26,27,28,29. Carprofen (10 mg/kg) is injected&#160;subcutaneously to provide relief from potential pain before surgery. The cranial window surgical procedures are identical to the AAV injection surgical procedures and are performed under aseptic conditions.
	<ol>
		<li>Anesthetize the mouse with 3% isoflurane. 
		NOTE: This is the initial dose and reduce to 2% for the surgery later on. During imaging, an intraperitoneal (IP) injection of 130 mg ketamine/10 mg xylazine/kg body weight dissolved in ACSF is used for anesthesia.</li>
		<li>Position the mouse on the mouse stereotaxic device and fix the head with ear bars. Apply ophthalmic ointment to eyes. Use a heating pad to keep the body temperature of the mouse at 37 &#176;C throughout the surgery. 
		NOTE: All surgical tools need to be sterilized.</li>
		<li>Make an incision of 5-8 mm long in the midline of the scalp and remove a flap of skin using a pair of scissors.</li>
		<li>After the skull is exposed, perform 2.0-3.0 mm diameter craniotomy using a high-speed drill over the virus injected area (i.e., motor cortex or somatosensory cortex, Figure 1B). First, make four small holes, and then drill along in a circle connecting the holes. Then, lift and remove the bone with sharp scissors and remove. The exposed dura mater can be removed or kept intact for impantation of the cranial window.</li>
		<li>Place a glass coverslip of 3-5 mm in diameter carrying a transparent silicone over the craniotomy. Use a toothpick to push the cranial window gently onto the surface of the brain. Then, seal the edge with a small amount of silicone adhesive. 
		NOTES: Alternatively, instead of silicone disk, 1.2% low melting point agarose gel can be used between the cover glass and the brain tissue.</li>
		<li>Finally, seal the edges of the coverslip with dental cement. Take care to apply the cement slightly at the edge of the cranial window for strong bonding. Attach a custom-made metal head plate to the skull with dental cement. 
		NOTE: The metal plate is used to fix the head of the mouse to the stage of 2-P microscope during the imaging session (Figure 1C).</li>
		<li>Add 0.5 mL of ACSF solution over the coverslip on the cranial window for water immersion during imaging.</li>
		<li>Perform time-lapse in vivo 2-P imaging of mito-GCaMP5G in astrocytes and mito-GCaMP6s in neurons with 910 nm wavelength through the cranial window (Figure 1C)18,20,27. 
		NOTE: During imaging, mice are on the heating pad to maintain physiological temperature. The mice will be sacrificed immediately after the imaging session is completed.</li>
		<li>Label astrocytes in vivo with sulforhodamine 101 (SR101) when it is necessary to determine colocalization.
		<ol>
			<li>At the end of step 3.3.4, apply 100 &#181;L of 100 &#181;M SR101 in ACSF on the cortical surface for 1-5 min.</li>
			<li>Rinse the surface with ACSF to wash away the unbound SR101. Using 2-P imaging, co-labeling of mito-GCaMP5G and SR101 in astrocytes can be observed 45-60 min later (Figure 4A).</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

In this article, we provide a method and protocol for imaging mitochondrial Ca2+&#160;signals in astrocytes and neurons. We implemented mitochondria-targeting and cell type-specific strategies to express GECI GCaMP5G/6s. To target GCaMP5G/6s in mitochondria, we included a mitochondria-targeting sequence in the plasmids. To express GCaMP5G/6s in astrocytes and neurons in vivo, we inserted an astrocyte-specific promoter gfaABC1D and neuron-specific promoter CaMKII into the plasmids. Cell-type specific e...

Mitochondria are dynamic subcellular organelles and are considered as the cell powerhouses for energy production. On the other hand, mitochondria can take up Ca2+ to the matrix in response to local or cytosolic Ca2+ rises. Mitochondrial Ca2+ uptake affects mitochondrial function, including metabolic processes such as reactions in the tricarboxylic acid (TCA) cycle and oxidative phosphorylation, and regulates Ca2+-sensitive proteins under physiological conditions1,2,3,4. Mitochondrial Ca2+ overloading is also a determinant for cell death, including necrosis and apoptosis in various brain disorders5,6,7. It causes the opening of mitochondrial permeability transition pores (mPTPs) and the release of caspase cofactor, which initiate apoptotic cell death. Therefore, it is important to study mitochondrial Ca2+ dynamics and handling in living cells to understand cellular physiology and pathology better.
Mitochondria maintain matrix Ca2+ homeostasis through a balance between Ca2+ uptake and efflux. Mitochondrial Ca2+ uptake is mainly mediated by mitochondrial Ca2+ uniporters (MCUs), while mitochondrial Ca2+ efflux is mediated by the Na+-Ca2+-Li+ exchangers (NCLXs) and the H+/Ca2+ exchangers (mHCXs)8. The balance can be perturbed through the stimulation of G-protein coupled receptors (GPCRs)9. Mitochondrial Ca2+ homeostasis is also affected by mitochondrial buffering by the formation of insoluble xCa2+-xPO4x-xOH complexes8.
Intracellular and mitochondrial changes in Ca2+ concentration ([Ca2+]) can be evaluated by fluorescent or luminescent Ca2+ indicators. Ca2+ binding to indicators causes spectral modifications, allowing to recording of free cellular [Ca2+] in real-time in live cells. Two types of probes are currently available to monitor Ca2+ changes in cells: organic chemical indicators and genetically-encoded Ca2+ indicators (GECIs). Generally, different variants with different Ca2+ affinities (based on Kd), spectral properties (excitation and emission wavelengths), dynamic ranges, and sensitivities are available for the biological questions under investigation. Although many synthetic organic Ca2+ indicators have been used for cytosolic Ca2+ imaging, only a few can be selectively loaded in the mitochondrial matrix for mitochondrial Ca2+ imaging, with Rhod-2 being the most widely used (for reviews see10,11). However, Rhod-2 has a major drawback of leakage during long time-course experiments; in addition, it is partitioned between mitochondria, other organelles and the cytosol, making absolute measurements in different subcompartments difficult. In contrast, by using cell-type specific promoters and subcellular compartment targeting sequences, GECIs can be expressed in different cell types and subcellular compartments for cell- and compartment-specific Ca2+ imaging in vitro or in vivo. Single-wavelength fluorescence intensity-based GCaMP Ca2+ indicators have recently emerged as major GECIs12,13,14,15,16. In this article, we provide a protocol for mitochondria-targeting and cell-type specific expression of GCaMP5G and GCaMP6s (GCaMP5G/6s) in astrocytes and neurons, and imaging mitochondrial Ca2+ uptake in these cell types. Using this protocol, the expression of GCaMP6G/6s in individual mitochondria can be revealed, and Ca2+ uptake in single mitochondrial resolution can be achieved in astrocytes and neurons in vitro and in vivo.

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imaging mitochondrial ca2+ uptake in astrocytes and neurons using genetically encoded ca2+ indicators (gecis)

Mitochondrial Ca2+ plays a critical role in controlling cytosolic Ca2+ buffering, energy metabolism, and cellular signal transduction. Overloading of mitochondrial Ca2+ contributes to various pathological conditions, including neurodegeneration and apoptotic cell death in neurological diseases. Here we present a cell-type specific and mitochondria targeting molecular approach for mitochondrial Ca2+ imaging in astrocytes and neurons in vitro and in vivo. We constructed DNA plasmids encoding mitochondria-targeting genetically encoded Ca2+ indicators (GECIs) GCaMP5G or GCaMP6s (GCaMP5G/6s) with astrocyte- and neuron-specific promoters gfaABC1D and CaMKII and mitochondria-targeting sequence (mito-). For in vitro mitochondrial Ca2+ imaging, the plasmids were transfected in cultured astrocytes and neurons to express GCaMP5G/6s. For in vivo mitochondrial Ca2+ imaging, adeno-associated viral vectors (AAVs) were prepared and injected into the mouse brains to express GCaMP5G/6s in mitochondria in astrocytes and neurons. Our approach provides a useful means to image mitochondrial Ca2+ dynamics in astrocytes and neurons to study the relationship between cytosolic and mitochondrial Ca2+ signaling, as well as astrocyte-neuron interactions.

The aim of this study was to provide a methodology to image mitochondrial Ca2+ signals using GECIs in astrocytes and neurons in vitro and in vivo. Results of both in vitro and in vivo mitochondrial Ca2+ imaging are presented here.
In vitro mitochondrial Ca2+ signaling in cultured astrocytes and neurons 
Mitochondrial Ca2+ uptake in as...

Watch this Scientific Journal Video about Imaging Mitochondrial Ca2+ Uptake in Astrocytes and Neurons using Genetically Encoded Ca2+ Indicators GECIs at JoVE.com

Imaging Mitochondrial Ca2+ Uptake in Astrocytes and Neurons using Genetically Encoded Ca2+ Indicators GECIs

This proctocol aims to provide a method for in vitro and in vivo mitochondrial Ca2+ imaging in astrocytes and neurons.

Imaging Mitochondrial Ca2+ Uptake in Astrocytes and Neurons using Genetically Encoded Ca2+ Indicators (GECIs)

Mitochondrial Ca2+ plays a critical role in controlling cytosolic Ca2+ buffering, energy metabolism, and cellular signal transduction. Overloading of ...

imaging-mitochondrial-ca2-uptake-astrocytes-neurons-using-genetically

Research

JoVE Journal

Neuroscience

4.0K Views.  University of Missouri-Columbia. This proctocol aims to provide a method for in vitro and in vivo mitochondrial Ca2+ imaging in astrocytes and neurons.

Video: Imaging Mitochondrial Ca2+ Uptake in Astrocytes and Neurons using Genetically Encoded Ca2+ Indicators GECIs

Analyses of Mitochondrial Calcium Influx in Isolated Mitochondria and Cultured Cells

Ca2+ handling by mitochondria is a critical function regulating both physiological and pathophysiological processes in a broad spectrum of cells. The ability to accurately measure the influx and efflux of Ca2+ from mitochondria is important for determining the role of mitochondrial Ca2+ handling in these processes. In this report, we present two methods for the measurement of mitochondrial Ca2+ handling in both isolated mitochondria and cultured cells. We first detail a plate reader-based platform for measuring mitochondrial Ca2+ uptake using the Ca2+ sensitive dye calcium green-5N. The plate reader-based format circumvents the need for specialized equipment, and the calcium green-5N dye is ideally suited for measuring Ca2+ from isolated tissue mitochondria. For our application, we describe the measurement of mitochondrial Ca2+ uptake in mitochondria isolated from mouse heart tissue; however, this procedure can be applied to measure mitochondrial Ca2+ uptake in mitochondria isolated from other tissues such as liver, skeletal muscle, and brain. Secondly, we describe a confocal microscopy-based assay for measurement of mitochondrial Ca2+ in permeabilized cells using the Ca2+ sensitive dye Rhod-2/AM and imaging using 2-dimensional laser-scanning microscopy. This permeabilization protocol eliminates cytosolic dye contamination, allowing for specific recording of changes in mitochondrial Ca2+. Moreover, laser-scanning microscopy allows for high frame rates to capture rapid changes in mitochondrial Ca2+ in response to various drugs or reagents applied in the external solution. This protocol can be applied to measure mitochondrial Ca2+ uptake in many cell types including primary cells such as cardiac myocytes and neurons, and immortalized cell lines.

Here, we present two protocols for the measurement of mitochondrial Ca2+ influx in isolated mitochondria and cultured cells. For isolated mitochondria, we detail a plate reader-based Ca2+ import assay using the Ca2+ sensitive dye calcium green-5N. For cultured cells, we describe a confocal microscopy method using the Ca2+ dye Rhod-2/AM.

Ca2+ handling by mitochondria is a critical function regulating both physiological and pathophysiological processes in a broad spectrum of cells. The ...

Biochemistry

Measuring Near Plasma Membrane and Global Intracellular Calcium Dynamics in Astrocytes

The brain contains glial cells.  Astrocytes, a type of glial cell, have long been known to provide a passive supportive role to neurons. However, increasing evidence suggests that astrocytes may also actively participate in brain function through functional interactions with neurons.  However, many fundamental aspects of astrocyte biology remain controversial, unclear and/or experimentally unexplored. One important issue is the dynamics of intracellular calcium transients in astrocytes. This is relevant because calcium is well established as an important second messenger and because it has been proposed that astrocyte calcium elevations can trigger the release of transmitters from astrocytes. However, there has not been any detailed or satisfying description of near plasma membrane calcium signaling in astrocytes. Total internal reflection fluorescence (TIRF) microscopy is a powerful tool to analyze physiologically relevant signaling events within about 100 nm of the plasma membrane of live cells. Here, we use TIRF microscopy and describe how to monitor near plasma membrane and global intracellular calcium dynamics almost simultaneously. The further refinement and systematic application of this approach has the potential to inform about the precise details of astrocyte calcium signaling. A detailed understanding of astrocyte calcium dynamics may provide a basis to understand if, how, when and why astrocytes and neurons undergo calcium-dependent functional interactions.

We describe how to measure near membrane and global intracellular calcium dynamics in cultured astrocytes using total internal reflection and epifluorescence microscopy.

The brain contains glial cells.  Astrocytes, a type of glial cell, have long been known to provide a passive supportive role to neurons. However, ...

Biology

Inducing Plasticity of Astrocytic Receptors by Manipulation of Neuronal Firing Rates

Close to two decades of research has established that astrocytes in situ and in vivo express numerous G protein-coupled receptors (GPCRs) that can be stimulated by neuronally-released transmitter. However, the ability of astrocytic receptors to exhibit plasticity in response to changes in neuronal activity has received little attention. Here we describe a model system that can be used to globally scale up or down astrocytic group I metabotropic glutamate receptors (mGluRs) in acute brain slices. Included are methods on how to prepare parasagittal hippocampal slices, construct chambers suitable for long-term slice incubation, bidirectionally manipulate neuronal action potential frequency, load astrocytes and astrocyte processes with fluorescent Ca2+ indicator, and measure changes in astrocytic Gq GPCR activity by recording spontaneous and evoked astrocyte Ca2+ events using confocal microscopy. In essence, a &#8220;calcium roadmap&#8221; is provided for how to measure plasticity of astrocytic Gq GPCRs. Applications of the technique for study of astrocytes are discussed. Having an understanding of how astrocytic receptor signaling is affected by changes in neuronal activity has important implications for both normal synaptic function as well as processes underlying neurological disorders and neurodegenerative disease.

Here we describe an adaptation of protocols used to induce homeostatic plasticity in neurons for the study of plasticity of astrocytic G protein-coupled receptors. Recently used to examine changes in astrocytic group I mGluRs in juvenile mice, the method can be applied to measure scaling of various astrocytic GPCRs, in tissue from adult mice in situ and in vivo, and to gain a better appreciation of the sensitivity of astrocytic receptors to changes in neuronal activity.

Close to two decades of research has established that astrocytes in situ and in vivo express numerous G protein-coupled receptors (GPCRs) that can be ...

Imaging Intracellular Ca2+ Signals in Striatal Astrocytes from Adult Mice Using Genetically-encoded Calcium Indicators

Astrocytes display spontaneous intracellular Ca2+ concentration fluctuations ([Ca2+]i) and in several settings respond to neuronal excitation with enhanced [Ca2+]i signals. It has been proposed that astrocytes in turn regulate neurons and blood vessels through calcium-dependent mechanisms, such as the release of signaling molecules. However, [Ca2+]i imaging in entire astrocytes has only recently become feasible with genetically encoded calcium indicators (GECIs) such as the GCaMP series. The use of GECIs in astrocytes now provides opportunities to study astrocyte [Ca2+]i signals in detail within model microcircuits such as the striatum, which is the largest nucleus of the basal ganglia. In the present report, detailed surgical methods to express GECIs in astrocytes in vivo, and confocal imaging approaches to record [Ca2+]i signals in striatal astrocytes in situ, are described. We highlight precautions, necessary controls and tests to determine if GECI expression is selective for astrocytes and to evaluate signs of overt astrocyte reactivity. We also describe brain slice and imaging conditions in detail that permit reliable [Ca2+]i imaging in striatal astrocytes in situ. The use of these approaches revealed the entire territories of single striatal astrocytes and spontaneous [Ca2+]i signals within their somata, branches and branchlets. The further use and expansion of these approaches in the striatum will allow for the detailed study of astrocyte [Ca2+]i signals in the striatal microcircuitry.

Imaging Intracellular Ca2+ Signals in Striatal Astrocytes from Adult Mice Using Genetically-encoded Calcium Indicators

The properties and functions of astrocyte intracellular Ca2+ signals in the striatum remain incompletely explored. We describe methods to express genetically encoded calcium indicators in striatal astrocytes using adeno-associated viruses of serotype 2/5 (AAV2/5), as well as procedures to reliably image Ca2+ signals within striatal astrocytes in situ.

Astrocytes display spontaneous intracellular Ca2+ concentration fluctuations ([Ca2+]i) and in several settings respond to neuronal excitation with ...

Monitoring Dynamic Changes In Mitochondrial Calcium Levels During Apoptosis Using A Genetically Encoded Calcium Sensor

Dynamic changes in intracellular calcium concentration in response to various stimuli regulates many cellular processes such as proliferation, differentiation, and apoptosis1. During apoptosis, calcium accumulation in mitochondria promotes the release of pro-apoptotic factors from the mitochondria into the cytosol2. It is therefore of interest to directly measure mitochondrial calcium in living cells in situ during apoptosis. High-resolution fluorescent imaging of cells loaded with dual-excitation ratiometric and non-ratiometric synthetic calcium indicator dyes has been proven to be a reliable and versatile tool to study various aspects of intracellular calcium signaling. Measuring cytosolic calcium fluxes using these techniques is relatively straightforward. However, measuring intramitochondrial calcium levels in intact cells using synthetic calcium indicators such as rhod-2 and rhod-FF is more challenging. Synthetic indicators targeted to mitochondria have blunted responses to repetitive increases in mitochondrial calcium, and disrupt mitochondrial morphology3. Additionally, synthetic indicators tend to leak out of mitochondria over several hours which makes them unsuitable for long-term experiments. Thus, genetically encoded calcium indicators based upon green fluorescent protein (GFP)4 or aequorin5 targeted to mitochondria have greatly facilitated measurement of mitochondrial calcium dynamics. Here, we describe a simple method for real-time measurement of mitochondrial calcium fluxes in response to different stimuli. The method is based on fluorescence microscopy of 'ratiometric-pericam' which is selectively targeted to mitochondria. Ratiometric pericam is a calcium indicator based on a fusion of circularly permuted yellow fluorescent protein and calmodulin4. Binding of calcium to ratiometric pericam causes a shift of its excitation peak from 415 nm to 494 nm, while the emission spectrum, which peaks around 515 nm, remains unchanged. Ratiometric pericam binds a single calcium ion with a dissociation constant in vitro of ~1.7 &mu;M4. These properties of ratiometric pericam allow the quantification of rapid and long-term changes in mitochondrial calcium concentration. Furthermore, we describe adaptation of this methodology to a standard wide-field calcium imaging microscope with commonly available filter sets. Using two distinct agonists, the purinergic agonist ATP and apoptosis-inducing drug staurosporine, we demonstrate that this method is appropriate for monitoring changes in mitochondrial calcium concentration with a temporal resolution of seconds to hours. Furthermore, we also demonstrate that ratiometric pericam is also useful for measuring mitochondrial fission/fragmentation during apoptosis. Thus, ratiometric pericam is particularly well suited for continuous long-term measurement of mitochondrial calcium dynamics during apoptosis.

This protocol describes a method for real-time measurement of mitochondrial calcium fluxes by fluorescent imaging. The method takes advantage of a circularly permutated YFP-based dual-excitation ratiometric calcium sensor (ratiometric pericam-mt) selectively expressed in mitochondria.

Dynamic changes in intracellular calcium concentration in response to various stimuli regulates many cellular processes such as proliferation, ...

Real-Time Fluorescent Measurement of Synaptic Functions in Models of Amyotrophic Lateral Sclerosis

Before neuronal degeneration, the cause of motor and cognitive deficits in patients with amyotrophic lateral sclerosis (ALS) and/or frontotemporal lobe dementia (FTLD) is dysfunction of communication between neurons and motor neurons and muscle. The underlying process of synaptic transmission involves membrane depolarization-dependent synaptic vesicle fusion and the release of neurotransmitters into the synapse. This process occurs through localized calcium influx into the presynaptic terminals where synaptic vesicles reside. Here, the protocol describes fluorescence-based live-imaging methodologies that reliably report depolarization-mediated synaptic vesicle exocytosis and presynaptic terminal calcium influx dynamics in cultured neurons.
Using a styryl dye that is incorporated into synaptic vesicle membranes, the synaptic vesicle release is elucidated. On the other hand, to study calcium entry, Gcamp6m is used, a genetically encoded fluorescent reporter. We employ high potassium chloride-mediated depolarization to mimic neuronal activity. To quantify synaptic vesicle exocytosis unambiguously, we measure the loss of normalized styryl dye fluorescence as a function of time. Under similar stimulation conditions, in the case of calcium influx, Gcamp6m fluorescence increases. Normalization and quantification of this fluorescence change are performed in a similar manner to the styryl dye protocol. These methods can be multiplexed with transfection-based overexpression of fluorescently tagged mutant proteins. These protocols have been extensively used to study synaptic dysfunction in models of FUS-ALS and C9ORF72-ALS, utilizing primary rodent cortical and motor neurons. These protocols easily allow for rapid screening of compounds that may improve neuronal communication. As such, these methods are valuable not only for the study of ALS but for all areas of neurodegenerative and developmental neuroscience research.

Two related methods are described to visualize subcellular events required for synaptic transmission. These protocols enable the real-time monitoring of the dynamics of presynaptic calcium influx and synaptic vesicle membrane fusion using live-cell imaging of in vitro cultured neurons.

Before neuronal degeneration, the cause of motor and cognitive deficits in patients with amyotrophic lateral sclerosis (ALS) and/or frontotemporal lobe ...

Live-imaging of Mitochondrial System in Cultured Astrocytes

While much attention has been given to mitochondrial alterations at the neuronal level, recent evidence demonstrates that mitochondrial dynamics and function in astrocytes are implicated in cognition. This article describes the method for time-lapse imaging of astrocyte cultures equipped with a mitochondrial biosensor: MitoTimer. MitoTimer is a powerful and unique tool to assess mitochondrial dynamics, mobility, morphology, biogenesis, and redox state. Here, the different procedures for culture, image acquisitions, and subsequent mitochondrial analysis are presented.

This article describes the method for mitochondrial time-lapse imaging of astrocyte cultures equipped with MitoTimer biosensor and the resulting multiparametric analysis of mitochondrial dynamics, mobility, morphology, biogenesis, redox state, and turnover.

While much attention has been given to mitochondrial alterations at the neuronal level, recent evidence demonstrates that mitochondrial dynamics and ...

Subcellular Imaging of Neuronal Calcium Handling In Vivo

Calcium (Ca2+) imaging has been largely used to examine neuronal activity, but it is becoming increasingly clear that subcellular Ca2+ handling is a crucial component of intracellular signaling. The visualization of subcellular Ca2+ dynamics in vivo,&#160;where neurons can be studied in their native, intact circuitry, has proven technically challenging in complex nervous systems. The transparency and relatively simple nervous system of the nematode Caenorhabditis elegans enable the cell-specific expression and in vivo visualization of fluorescent tags and indicators. Among these are fluorescent indicators that have been modified for use in the cytoplasm as well as various subcellular compartments, such as the mitochondria. This protocol enables non-ratiometric Ca2+ imaging in vivo with a subcellular resolution that permits the analysis of Ca2+ dynamics down to the level of individual dendritic spines and mitochondria. Here, two available genetically encoded indicators with different Ca2+ affinities are used to demonstrate the use of this protocol for measuring relative Ca2+ levels within the cytoplasm or mitochondrial matrix in a single pair of excitatory interneurons (AVA). Together with the genetic manipulations and longitudinal observations possible in C. elegans, this imaging protocol may be useful for answering questions regarding how Ca2+ handling regulates neuronal function and plasticity.

Subcellular Imaging of Neuronal Calcium Handling In Vivo

The current methods describe a non-ratiometric approach for high-resolution, sub-compartmental calcium imaging in vivo in Caenorhabditis elegans using readily available genetically encoded calcium indicators.

Calcium (Ca2+) imaging has been largely used to examine neuronal activity, but it is becoming increasingly clear that subcellular Ca2+ handling is a ...

Simultaneous Measurement of Mitochondrial Calcium and Mitochondrial Membrane Potential in Live Cells by Fluorescent Microscopy

Apart from their essential role in generating ATP, mitochondria also act as local calcium (Ca2+) buffers to tightly regulate intracellular Ca2+ concentration. To do this, mitochondria utilize the electrochemical potential across their inner membrane (&#916;&#936;m) to sequester Ca2+. The influx of Ca2+ into the mitochondria stimulates three rate-limiting dehydrogenases of the citric acid cycle, increasing electron transfer through the oxidative phosphorylation (OXPHOS) complexes. This stimulation maintains &#916;&#936;m, which is temporarily dissipated as the positive calcium ions cross the mitochondrial inner membrane into the mitochondrial matrix.
We describe here a method for simultaneously measuring mitochondria Ca2+ uptake and &#916;&#936;m in live cells using confocal microscopy. By permeabilizing the cells, mitochondrial Ca2+ can be measured using the fluorescent Ca2+ indicator Fluo-4, AM, with measurement of &#916;&#936;m using the fluorescent dye tetramethylrhodamine, methyl ester, perchlorate (TMRM). The benefit of this system is that there is very little spectral overlap between the fluorescent dyes, allowing accurate measurement of mitochondrial Ca2+ and &#916;&#936;m simultaneously. Using the sequential addition of Ca2+ aliquots, mitochondrial Ca2+ uptake can be monitored, and the concentration at which Ca2+ induces mitochondrial membrane permeability transition and the loss of &#916;&#936;m determined.

Mitochondria can utilize the electrochemical potential across their inner membrane (&#916;&#936;m) to sequester calcium (Ca2+), allowing them to shape cytosolic Ca2+ signaling within the cell. We describe a method for simultaneously measuring mitochondria Ca2+ uptake and &#916;&#936;m in live cells using fluorescent dyes and confocal microscopy.

Apart from their essential role in generating ATP, mitochondria also act as local calcium (Ca2+) buffers to tightly regulate intracellular Ca2+ ...

Fluorescence-Based Monitoring of Mitochondrial Stress in Astrocytes

Source: Espourteille, J., et al. <a href="https://app.jove.com/v/62957">Live-imaging of Mitochondrial System in Cultured Astrocytes.</a> J. Vis. Exp. (2021)
This video demonstrates the evaluation of mitochondrial health in genetically modified astrocytes, which express a fluorescent protein within their mitochondria. The protein helps to track changes in mitochondrial health as its fluorescence changes from green to red, indicating stress or damage. Images are captured and analyzed using various parameters.

1. Rat hippocampal astrocyte primary culture

	Sacrifice five rat pups (Wistar IGS Rat) by decapitation at postnatal days 1-2.
	Remove the brain and keep ...

Imaging Mitochondrial Ca²⁺ Uptake in Astrocytes and Neurons using Genetically Encoded Ca²⁺ Indicators (GECIs)

Summary

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Chapters in this video

Analyses of Mitochondrial Calcium Influx in Isolated Mitochondria and Cultured Cells

Measuring Near Plasma Membrane and Global Intracellular Calcium Dynamics in Astrocytes

Inducing Plasticity of Astrocytic Receptors by Manipulation of Neuronal Firing Rates

Imaging Intracellular Ca²⁺ Signals in Striatal Astrocytes from Adult Mice Using Genetically-encoded Calcium Indicators

Monitoring Dynamic Changes In Mitochondrial Calcium Levels During Apoptosis Using A Genetically Encoded Calcium Sensor

Real-Time Fluorescent Measurement of Synaptic Functions in Models of Amyotrophic Lateral Sclerosis

Live-imaging of Mitochondrial System in Cultured Astrocytes

Subcellular Imaging of Neuronal Calcium Handling In Vivo

Simultaneous Measurement of Mitochondrial Calcium and Mitochondrial Membrane Potential in Live Cells by Fluorescent Microscopy

Fluorescence-Based Monitoring of Mitochondrial Stress in Astrocytes