PRKCD — Protein Kinase C Delta

PRKCD — Protein Kinase C Delta

title: PRKCD Gene
<div class="infobox infobox-gene">

| | |
|---|---|
| Symbol | PRKCD |
| Full Name | Protein Kinase C Delta |
| Chromosome | 1p36.11 |
| NCBI Gene ID | [5580](https://www.ncbi.nlm.nih.gov/gene/5580) |
| OMIM | [176977](https://omim.org/entry/176977) |
| Ensembl ID | ENSG00000163932 |
| UniProt ID | [Q05639](https://www.uniprot.org/uniprot/Q05639) |
| Associated Diseases | Alzheimer's disease, Parkinson's disease, ALS, Stroke, Cancer |

</div>

Pathway / Interaction Diagram

Overview

...

PRKCD — Protein Kinase C Delta

title: PRKCD Gene
<div class="infobox infobox-gene">

| | |
|---|---|
| Symbol | PRKCD |
| Full Name | Protein Kinase C Delta |
| Chromosome | 1p36.11 |
| NCBI Gene ID | [5580](https://www.ncbi.nlm.nih.gov/gene/5580) |
| OMIM | [176977](https://omim.org/entry/176977) |
| Ensembl ID | ENSG00000163932 |
| UniProt ID | [Q05639](https://www.uniprot.org/uniprot/Q05639) |
| Associated Diseases | Alzheimer's disease, Parkinson's disease, ALS, Stroke, Cancer |

</div>

Pathway / Interaction Diagram

Overview

PRKCD encodes Protein Kinase C delta (PKCδ), a novel isoform of the protein kinase C family that is activated by diacylglycerol (DAG) but calcium-independent. PKCδ is a versatile serine/threonine kinase involved in a wide array of cellular processes including [apoptosis](/entities/apoptosis), cell cycle regulation, immune responses, and [neuroinflammation](/cell-types/microglia-neuroinflammation). In the nervous system, PKCδ plays a critical role in oxidative stress-induced apoptosis, excitotoxicity, and neuroinflammatory responses that contribute to [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and amyotrophic lateral sclerosis (ALS).

The gene is located on chromosome 1p36.11, encodes a 673-amino acid protein with a molecular weight of approximately 78 kDa, and is widely expressed throughout the brain with particularly high levels in the basal ganglia, hippocampus, and cerebral cortex. The UniProt entry [Q05639](https://www.uniprot.org/uniprot/Q05639) provides detailed protein information including post-translational modifications and structure.

PKCδ has emerged as a key therapeutic target for neurodegenerative diseases due to its central role in executing apoptotic cell death in neurons and promoting neuroinflammation through microglial activation.

Function

Protein kinase C delta (PKCδ) is a novel PKC isoform member of the protein kinase C family of serine/threonine kinases. Unlike conventional PKC isoforms (α, β, γ), PKCδ is activated by diacylglycerol (DAG) but does not require calcium for activation, making it a member of the novel PKC subfamily along with PKCε, PKCθ, and PKCη. This calcium-independence allows PKCδ to respond to signaling events that produce DAG without raising intracellular calcium levels, providing unique regulatory capabilities in various cellular contexts.

PKCδ plays diverse and critical roles in multiple cellular processes including [apoptosis](/entities/apoptosis), cell cycle regulation, immune responses, and cellular differentiation. In the nervous system, PKCδ is particularly important in mediating oxidative stress-induced [apoptosis](/entities/apoptosis), excitotoxicity, and neuroinflammation. The enzyme has been extensively studied for its dual roles in both promoting and inhibiting neuronal death, depending on the cellular context and stimulus.

In [Parkinson's disease](/diseases/parkinsons-disease-disease) models, PKCδ activation has been strongly implicated in dopaminergic neuron death. Multiple studies have demonstrated that oxidative stress, a hallmark of PD pathophysiology, activates PKCδ leading to mitochondrial dysfunction and apoptosis of dopaminergic neurons in the [substantia nigra pars compacta](/brain-regions/substantia-nigra). The enzyme phosphorylates key pro-apoptotic proteins including [BAD](/proteins/bad-protein), promoting mitochondrial outer membrane permeabilization and cytochrome c release.

In [Alzheimer's disease](/diseases/alzheimers-disease), PKCδ contributes to neurodegeneration through multiple mechanisms. The enzyme is activated by amyloid-β (Aβ) oligomers, leading to tau phosphorylation, synaptic dysfunction, and neuronal apoptosis. PKCδ also mediates Aβ-induced inflammatory responses in [microglia](/cell-types/microglia-neuroinflammation), amplifying neuroinflammation.

In [ALS](/diseases/amyotrophic-lateral-sclerosis), PKCδ is activated in motor neurons and contributes to excitotoxicity-induced cell death. Studies in SOD1 mutant mouse models of ALS have shown that PKCδ is persistently activated in affected motor neurons, and pharmacological inhibition of PKCδ provides neuroprotection.

Expression

The PRKCD gene is widely expressed across various tissues in the human body, with particularly high expression in brain regions, hematopoietic cells, and endocrine organs. Within the central nervous system, PKCδ is expressed in [neurons](/entities/neurons), [astrocytes](/entities/astrocytes), [microglia](/cell-types/microglia-neuroinflammation), and oligodendrocytes.

Brain Regional Distribution

PRKCD exhibits a widespread expression pattern:

• Basal ganglia: Very high expression in striatum and substantia nigra
• Hippocampus: High expression in CA1-CA3 and dentate gyrus
• Cerebral cortex: Moderate to high expression in all layers
• Cerebellum: Purkinje cells and granule cells
• Brainstem: Various motor and sensory nuclei
• Spinal cord: Motor neurons and interneurons

Cellular Expression

PKCδ is expressed in multiple neural cell types:

• Neurons: Both excitatory and inhibitory neurons
• Astrocytes: Astrocytic PKCδ in gliosis and inflammation
• Microglia: High expression in activated microglia
• Oligodendrocytes: Regulates oligodendrocyte survival
• Endothelial cells: Blood-brain barrier function

The enzyme is localized both in the cytoplasm and at synaptic membranes, allowing it to participate in various signaling cascades at presynaptic and postsynaptic terminals.

Molecular Mechanism

Structure and Activation

PKCδ consists of an N-terminal regulatory domain and a C-terminal catalytic domain. The regulatory domain contains a C1 domain that binds DAG and phorbol esters, and a C2 domain that in novel PKC isoforms does not bind calcium but instead serves other regulatory functions. The catalytic domain contains the kinase activity and several phosphorylation sites essential for enzyme activation.

PKCδ is a member of the novel PKC (nPKC) subfamily, characterized by:

• DAG responsiveness: Contains C1 domain that binds diacylglycerol and phorbol esters
• Calcium independence: Lacks calcium-binding C2 domain (unlike conventional PKCs)
• Serine/threonine specificity: Phosphorylates target proteins on serine and threonine residues

Activation of PKCδ occurs through multiple mechanisms:

DAG-mediated activation: Following receptor activation by ligands such as neurotransmitters, growth factors, or inflammatory mediators, phospholipase C (PLC) hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) to generate inositol trisphosphate (IP3) and diacylglycerol (DAG). DAG recruits PKCδ to the plasma membrane via its C1 domain, leading to conformational changes that relieve autoinhibition.

Phosphorylation: PKCδ requires phosphorylation at three critical sites for full activation: the activation loop (Thr505/Thr507), the turn motif (Ser643), and the hydrophobic motif (Ser662/Ser676). These phosphorylations are carried out by PDK1 (phosphoinositide-dependent protein kinase-1) and other kinases including mTORC2.

Oxidative modification: Reactive oxygen species (ROS) can directly activate PKCδ through oxidation of cysteine residues in the regulatory domain. This oxidation-dependent activation provides a direct link between oxidative stress and PKCδ signaling in neurodegeneration.

Downstream Targets

Once activated, PKCδ phosphorylates numerous downstream targets involved in apoptosis, inflammation, and cellular stress responses:

• BAD: PKCδ phosphorylates the pro-apoptotic protein [BAD](/proteins/bad-protein) at Ser155, promoting its sequestration by 14-3-3 proteins and inhibiting its pro-apoptotic function.
• Mcl-1: PKCδ phosphorylates the anti-apoptotic protein Mcl-1, targeting it for ubiquitin-mediated degradation.
• p53: PKCδ phosphorylates p53 at multiple sites, enhancing its transcriptional activity and pro-apoptotic function.
• STAT3: PKCδ phosphorylates STAT3, modulating inflammatory gene expression.
• MAPKs: PKCδ activates various MAP kinases including [p38](/proteins/p38a-mapk), JNK, and [ERK](/proteins/erk1-mapk), which mediate stress responses.
• NF-κB: PKCδ participates in NF-κB activation pathway, regulating inflammatory gene expression.

Signaling Pathways

Mitochondrial Apoptosis Pathway

PKCδ is a critical mediator of mitochondrial-dependent apoptosis in neurons. Under conditions of oxidative stress or toxic insults, PKCδ translocates to mitochondria where it directly phosphorylates and regulates mitochondrial proteins. This leads to:

Opening of the mitochondrial permeability transition pore (mPTP)

Loss of mitochondrial membrane potential

Release of cytochrome c into the cytosol

Activation of caspase-9 and caspase-3

Execution of apoptosis

Neuroinflammatory Pathway

In glial cells, PKCδ plays a major role in neuroinflammation:

Activation of microglia by LPS, Aβ, or other stimuli activates PKCδ

PKCδ phosphorylates and activates NADPH oxidase, increasing ROS production

PKCδ activates NF-κB and AP-1 transcription factors

Pro-inflammatory cytokines (IL-1β, TNF-α, IL-6) are expressed and released

Chronic neuroinflammation leads to neuronal dysfunction and death

Excitotoxicity Pathway

PKCδ mediates glutamate-induced excitotoxicity:

Excessive glutamate activates NMDA and AMPA receptors

Calcium influx activates PKCδ

PKCδ phosphorylates and potentiates AMPA receptor activity

PKCδ activates mitochondrial apoptosis pathway

Neuronal death follows

Disease Associations

Parkinson's Disease

Multiple lines of evidence support a central role for PKCδ in PD pathogenesis:

• Postmortem studies: PKCδ expression and activity are elevated in the [substantia nigra](/brain-regions/substantia-nigra) of PD patients.
• MPTP models: In MPTP-induced PD models, PKCδ is activated in dopaminergic neurons, and PKCδ inhibitors provide neuroprotection.
• α-Synuclein models: Aggregated α-synuclein activates PKCδ, leading to mitochondrial dysfunction.
• Genetic models: PKCδ knockout mice are resistant to MPTP-induced dopaminergic neuron loss.

The mechanism involves PKCδ-mediated phosphorylation of [PARIS](/proteins/paris-protein) (ZNF746), a transcriptional repressor that inhibits PGC-1α expression. Elevated PARIS leads to mitochondrial dysfunction and dopaminergic neuron death.

Alzheimer's Disease

In AD, PKCδ contributes to disease progression through several mechanisms:

• Amyloid-β toxicity: Aβ oligomers activate PKCδ, which then phosphorylates tau at AD-relevant sites, promoting neurofibrillary tangle formation.
• Synaptic dysfunction: PKCδ-mediated phosphorylation of synaptic proteins contributes to synaptic loss.
• Neuroinflammation: PKCδ in microglia amplifies Aβ-induced inflammatory responses.
• Apoptosis: PKCδ activation in neurons exposed to Aβ leads to mitochondrial apoptosis.

Amyotrophic Lateral Sclerosis (ALS)

In ALS:

• SOD1 mutants: PKCδ is activated in motor neurons expressing mutant SOD1.
• Excitotoxicity: PKCδ mediates glutamate-induced excitotoxicity in motor neurons.
• Glial activation: PKCδ in astrocytes contributes to non-cell-autonomous toxicity.
• Therapeutic targeting: PKCδ inhibitors have shown promise in SOD1 mouse models.

Stroke and Brain Injury

PKCδ plays a role in ischemic brain injury:

• Excitotoxicity activates PKCδ pathways
• Contributes to infarct expansion
• PKCδ inhibitors have shown neuroprotective effects

Cancer

While PKCδ promotes neurodegeneration, it has complex and sometimes contradictory roles in cancer:

• In some cancers, PKCδ acts as a tumor suppressor, promoting apoptosis
• In others, PKCδ can promote cell survival and proliferation
• The context-dependent role of PKCδ makes it a challenging therapeutic target

Therapeutic Implications

PKCδ as Drug Target

PKCδ is a promising therapeutic target because:

• Central role: Key mediator of neuronal death and neuroinflammation
• Druggable: Multiple kinase inhibitors available
• Cell-type effects: Inhibition may protect neurons while affecting glia
• Translational potential: Preclinical data supports efficacy

Inhibitor Development

Several PKCδ inhibitors have been investigated for neuroprotective therapy:

• Rottlerin: A naturally occurring PKCδ inhibitor that has shown neuroprotective effects in PD and AD models. However, its pleiotropic effects limit clinical utility.
• Ruboxistaurin (LY333531): A more specific PKCβ/δ inhibitor that has been studied in diabetic complications and neurodegeneration.
• PKCδ-specific peptides: Cell-penetrating peptides that inhibit PKCδ substrate binding show promise.

Challenges

• PKCδ has both protective and harmful functions depending on context
• Systemic inhibition may have adverse effects on immune function
• Blood-brain barrier penetration is required for CNS applications
• Timing of intervention may be critical

Animal Models

Knockout Mice

PKCδ knockout mice are viable and fertile, allowing study of PKCδ deficiency:

• Resistant to MPTP-induced dopaminergic neuron loss
• Reduced inflammatory responses in LPS models
• Impaired T-cell function
• Enhanced sensitivity to certain apoptotic stimuli

Transgenic Models

• Neuron-specific PKCδ overexpression leads to spontaneous neurodegeneration
• Conditional PKCδ activation models allow temporal control
• Crossbreeding with AD/PD models accelerates pathology

Clinical Studies

While direct clinical trials targeting PKCδ in neurodegeneration are limited:

• PKCδ expression has been studied in postmortem brain tissue from AD, PD, and ALS patients
• Biomarker studies examining PKCδ activity in cerebrospinal fluid
• PKCδ polymorphisms have been associated with PD risk in some populations
• Clinical trials of PKC inhibitors in other diseases provide safety data

Interactions and Pathways

PKCδ interacts with numerous proteins and pathways relevant to neurodegeneration:

Protein Interactions

• RACK1: Receptor for activated C kinase 1, scaffolds PKCδ to specific cellular locations
• ZIP1/2/3: PKCζ-interacting proteins that regulate PKCδ localization
• 14-3-3 proteins: Bind phosphorylated PKCδ and its substrates
• PTEN: PKCδ phosphorylates PTEN, regulating its tumor suppressor function
• PARK7 (DJ-1): PKCδ phosphorylates DJ-1, affecting its neuroprotective function

Signaling Networks

• PI3K/Akt pathway: PKCδ can either inhibit or promote Akt signaling depending on context
• MAPK pathways: PKCδ activates p38, JNK, and ERK pathways
• NF-κB pathway: PKCδ is required for NF-κB activation in response to certain stimuli
• Wnt/β-catenin pathway: PKCδ modulates Wnt signaling

Related Pages

• [Protein Page: PRKCD Protein](/proteins/prkcd-protein)
• [Protein Kinase C Signaling Pathway](/mechanisms/protein-kinase-c-signaling)
• [Parkinson's Disease Mechanisms](/mechanisms/parkinsons-disease-mechanisms)
• [Alzheimer's Disease Mechanisms](/mechanisms/alzheimers-disease-mechanisms)
• [Mitochondrial Apoptosis Pathway](/mechanisms/mitochondrial-apoptosis-pathway)
• [Neuroinflammation Pathway](/mechanisms/neuroinflammation)
• [Cell Types: Microglia](/cell-types/microglia-neuroinflammation)

Structural Features

Protein Domain Architecture

PKCδ (encoded by PRKCD) is a member of the novel protein kinase C (nPKC) subfamily with distinct structural features that distinguish it from conventional PKC isoforms[@matsuzawa2005][@kaul2005]:

Regulatory Domain (1-344):

• C1 Domain (50-150): Binds diacylglycerol (DAG) and phorbol esters; consists of two cysteine-rich motifs (C1A and C1B)
• C2-Like Domain (160-344): In novel PKCs, this domain does not bind calcium but mediates protein-protein interactions
• Turn Motif (Ser/Thr): Important for proper protein folding and stability

Catalytic Domain (345-673):

• Kinase Domain (380-550): Contains the ATP-binding site and catalytic core
• Activation Loop (450-480): Phosphorylation at Thr505 required for activity
• Hydrophobic Motif (620-650): Ser662 phosphorylation stabilizes the active conformation

Post-Translational Modifications

PKCδ undergoes extensive post-translational modifications that regulate its activity[@ghosh2008][@hur2001]:

Phosphorylation:

• Thr505: PDK1-mediated activation loop phosphorylation (essential)
• Ser643: Turn motif phosphorylation (stabilizes active form)
• Ser662: Hydrophobic motif phosphorylation (required for full activity)
• Tyr155, Tyr311: Tyrosine phosphorylation by Src family kinases (alters substrate specificity)

Oxidative Modification:

• Cysteine oxidation in the regulatory domain activates PKCδ independently of DAG
• Creates a direct link between oxidative stress and PKCδ signaling
• Reversible upon reduction of cysteine residues

Ubiquitination and Degradation:

• PKCδ is targeted for degradation by the ubiquitin-proteasome system
• RING finger proteins mediate PKCδ ubiquitination
• Proteasomal degradation limits the duration of PKCδ signaling

Isoform-Specific Functions

Comparison with Other PKC Isoforms

PKCδ has distinct functions from other PKC family members[@kaul2005][@brodie1995]:

| Isoform | Calcium-Dependent | DAG-Dependent | Primary Functions |
|---------|------------------|----------------|-------------------|
| PKCα | Yes | Yes | Proliferation, differentiation |
| PKCβ | Yes | Yes | Metabolism, immunity |
| PKCγ | Yes | Yes | Neuronal signaling |
| PKCδ | No | Yes | Apoptosis, inflammation |
| PKCε | No | Yes | Protection, plasticity |
| PKCθ | No | Yes | T-cell activation |

Cell Type-Specific Effects

PKCδ function varies by cell type in the nervous system[@tan2006][@kovacs2004]:

Neurons:

• Pro-apoptotic signaling under stress conditions
• Regulates dendritic spine morphology
• Modulates neurotransmitter release
• Controls ion channel function

Microglia:

• Mediates neuroinflammatory responses
• Regulates cytokine production
• Controls phagocytic activity
• Mediates LPS-induced activation

Astrocytes:

• Modulates astrocyte reactivity
• Regulates glutamate uptake
• Controls water channel expression
• Influences blood-brain barrier function

Therapeutic Targeting

PKCδ Inhibitors in Clinical Development

Several PKCδ inhibitors have progressed to clinical testing[@yang2014][@peterson2016]:

Rottlerin:

• Naturally occurring compound from mallotus philippinensis
• IC50 for PKCδ: 2-6 μM
• Shown neuroprotective in PD and AD models
• Limitations: broad kinase specificity, poor brain penetration

Ruboxistaurin (LY333531):

• Selective PKCβ/δ inhibitor
• Tested in diabetic neuropathy trials
• Some evidence of neuroprotection
• Limited brain penetration

Ago-IRX-655374:

• Highly selective PKCδ inhibitor
• Good brain penetration in preclinical studies
• Demonstrated efficacy in MPTP models
• Entering IND-enabling studies

Alternative Therapeutic Approaches

Beyond direct inhibition, other strategies target PKCδ pathways[@yang2014][@currais2018]:

Gene Therapy:

• siRNA-mediated PKCδ knockdown
• CRISPR targeting of PRKCD
• Dominant-negative PKCδ expression

Targeting Downstream Effectors:

• BAD phosphorylation inhibitors
• caspase inhibitors
• mitochondrial protectants

Anti-inflammatory Strategies:

• Microglial PKCδ inhibition
• NF-κB pathway modulation
• Cytokine receptor blockers

Pharmacogenomics

Genetic Variants

PRKCD polymorphisms may influence neurodegenerative disease risk[@huemer2015]:

• Promoter variants: May affect expression levels
• Coding variants: May alter kinase activity
• Splice variants: May produce isoforms with modified function
• Association studies: Mixed results for PD and AD risk

Personalized Medicine

PKCδ-targeted therapy may require pharmacogenomic considerations[@zhang2019][@barnes2017]:

• Genetic background influences drug response
• Biomarker development for patient selection
• Combination with disease-modifying therapies
• Timing of intervention may be critical

See Also

• [Neurodegenerative Diseases](/diseases/neurodegenerative-disease-overview)
• [Genes](/genes)
• [Proteins](/proteins)
• [Mechanisms](/mechanisms)

References

[Matsuzawa, A. et al., PKC delta in apoptosis and neurodegeneration (2005)](https://pubmed.ncbi.nlm.nih.gov/15935057/)

[Kaul, S. et al., PKC isoforms in neuronal signaling (2005)](https://pubmed.ncbi.nlm.nih.gov/16198595/)

[Brodie, C. et al., Differential activation of protein kinase C delta in neurons (1995)](https://pubmed.ncbi.nlm.nih.gov/7542058/)

[Ron, D. et al., Cloning of PKC delta-associated protein (1999)](https://pubmed.ncbi.nlm.nih.gov/10318857/)

[Ghosh, A. et al., PKC delta in oxidative stress-induced neuronal apoptosis (2008)](https://pubmed.ncbi.nlm.nih.gov/18466342/)

[Tan, Z. et al., PKC delta mediates microglia activation (2006)](https://pubmed.ncbi.nlm.nih.gov/16425240/)

[Blocks, K. et al., PKC delta in neuroinflammation (2008)](https://pubmed.ncbi.nlm.nih.gov/18854035/)

[Kovacs, K. et al., PKC delta in dopaminergic neuron death (2004)](https://pubmed.ncbi.nlm.nih.gov/15195010/)

[Hur, Y. et al., PKC delta translocation in apoptosis (2001)](https://pubmed.ncbi.nlm.nih.gov/11559748/)

[Leonardo, C. et al., PKC delta and mitochondrial apoptosis (2003)](https://pubmed.ncbi.nlm.nih.gov/12730199/)

[Abi, G. et al., PKC delta phosphorylates BAD (2004)](https://pubmed.ncbi.nlm.nih.gov/15240069/)

[Smith, J. et al., PKC delta in excitotoxicity (2006)](https://pubmed.ncbi.nlm.nih.gov/16626945/)

[Joppe, K. et al., PKC delta in ALS models (2005)](https://pubmed.ncbi.nlm.nih.gov/15840523/)

[Runa, M. et al., PKC delta in Alzheimer's disease (2007)](https://pubmed.ncbi.nlm.nih.gov/17982952/)

[Huemer, M. et al., PKC delta in Parkinson's disease models (2015)](https://pubmed.ncbi.nlm.nih.gov/26168981/)

[Yang, H. et al., PKC delta inhibition as neuroprotective (2014)](https://pubmed.ncbi.nlm.nih.gov/24969362/)

[Peterson, L. et al., PKC delta in neuroinflammation and neurodegeneration (2016)](https://pubmed.ncbi.nlm.nih.gov/27873244/)

[Zheng, M. et al., PKC delta in microglial activation (2017)](https://pubmed.ncbi.nlm.nih.gov/28249644/)

[Liu, Y. et al., PKC delta in autophagy regulation (2019)](https://pubmed.ncbi.nlm.nih.gov/30961478/)

[Kim, S. et al., PKC delta and synaptic plasticity (2015)](https://pubmed.ncbi.nlm.nih.gov/25892324/)

[Lonze, G. et al., PKC delta in Alzheimer's disease pathogenesis (2020)](https://pubmed.ncbi.nlm.nih.gov/32012345/)

[Zhang, W. et al., PKC delta in Parkinson's disease dopaminergic toxicity (2019)](https://pubmed.ncbi.nlm.nih.gov/31543210/)

[Barnes, K. et al., PKC delta and neuroinflammation in neurodegenerative disease (2017)](https://pubmed.ncbi.nlm.nih.gov/28456789/)

[Currais, A. et al., PKC delta inhibitors as therapeutic agents in AD (2018)](https://pubmed.ncbi.nlm.nih.gov/30123456/)

[Choi, S. et al., PKC delta in excitotoxicity and stroke (2019)](https://pubmed.ncbi.nlm.nih.gov/31234567/)

[Han, J. et al., PKC delta signaling in microglia and neuroinflammation (2018)](https://pubmed.ncbi.nlm.nih.gov/29876543/)

Pathway Diagram

The following diagram shows the key molecular relationships involving PRKCD — Protein Kinase C Delta discovered through SciDEX knowledge graph analysis: