PDGFD Human

What is the molecular structure of human PDGF-D?

Human PDGF-D consists of an N-terminal CUB (complement subcomponents C1r/C1s, Uegf, and Bmp1) domain and a C-terminal PDGF/vascular endothelial growth factor domain . Unlike traditional PDGF family members (PDGF-A and PDGF-B), PDGF-D requires proteolytic removal of its CUB domain to activate PDGF receptors . The protein forms disulfide-bonded homodimers but does not heterodimerize with PDGF-A or PDGF-B chains . The recombinant form used in many laboratory applications comprises amino acids Asp253-Arg370 with accession number Q9GZP0 .

How does PDGF-D differ from other PDGF family members?

PDGF-D, also named spinal cord-derived growth factor B (SCDGF-B), differs from classical PDGF family members in several key ways . Unlike PDGF-A and PDGF-B which are secreted in active forms, PDGF-D contains an N-terminal CUB domain that requires proteolytic cleavage for receptor activation . Additionally, while PDGF-A and PDGF-B can form both homodimers and heterodimers, PDGF-D (like PDGF-C) only forms homodimers . These structural differences impact receptor specificity, with PDGF-D primarily signaling through the PDGF-β receptor rather than through multiple receptor combinations .

What is the activation mechanism of PDGF-D?

PDGF-D is secreted as a latent form that requires extracellular proteolytic processing to become biologically active . The processing involves removal of the N-terminal CUB domain, which exposes the PDGF/VEGF domain needed for receptor binding and activation . Research in prostate cancer cell lines has demonstrated that some cells, such as LNCaP cells, can auto-activate latent PDGF-D into its active form, which then induces phosphorylation of the β-PDGF receptor . This activation mechanism represents an important regulatory step in PDGF-D signaling that distinguishes it from other growth factors that are secreted in active forms.

What genetic factors regulate PDGF-D expression?

PDGF-D expression is regulated by several genetic factors, including transcription factors FOXC1 and FOXC2 . The SNP rs2019090 at the 11q22.3 locus significantly influences PDGF-D expression levels . This polymorphism is multi-allelic with A as the reference allele and T, C, and G as alternatives . Position weight matrix analyses show that the T allele decreases FOXC1/C2 binding affinity to the regulatory region, resulting in reduced PDGF-D expression . CRISPR interference (CRISPRi) experiments utilizing dCas9KRAB with specific guide RNAs have confirmed the regulatory relationship between these factors and PDGF-D expression .

How do genetic variations in PDGF-D affect phenotypes in animal models?

Genetic variations in PDGF-D have been associated with phenotypic differences in animal models, particularly in sheep tail morphology . Analysis of polymorphisms like g.4122606 C>G and g.3852134 C>T has revealed significant associations with tail measurements . For example, sheep with the GG genotype at g.4122606 C>G showed significantly smaller tail width (19.168 ± 0.204 cm) compared to those with the CC genotype (19.940 ± 0.276 cm) . Similarly, the TT genotype at g.3852134 C>T was associated with significantly larger tail length measurements (12.996 ± 1.382 cm) compared to the CC genotype (9.657 ± 0.089 cm) . These variations affect transcription factor binding in the PDGF-D promoter region, potentially altering gene expression and subsequent developmental outcomes.

What experimental approaches can be used to manipulate PDGF-D expression?

Several experimental approaches have proven effective for manipulating PDGF-D expression:

• Viral vector systems: Lentiviral vectors carrying PDGF-D have been successfully used for overexpression in cell culture models, such as preadipocytes . Adenoviral constructs encoding PDGF-D are effective for in vivo delivery in animal models .

• Gene silencing: CRISPRi with dCas9KRAB and specific guide RNAs has effectively suppressed PDGF-D expression in human coronary artery smooth muscle cells (HCASMC) .

• Tissue-specific expression: AAV vectors with tissue-specific promoters (such as RPE-specific VDM2 promoter) can drive localized PDGF-D expression in target tissues .

• Transgenic models: Mice with PDGF-D expressed in basal epidermal cells have been created to study its role in skin biology and wound healing .

When implementing these approaches, researchers should consider target cell type, duration of expression required, and potential off-target effects that may influence experimental outcomes.

What are the primary cellular effects of PDGF-D signaling?

PDGF-D exerts multiple cellular effects through activation of PDGF receptors, primarily PDGFR-β . Key cellular responses include:

• Mitogenic activity: PDGF-D is a potent stimulator of cell proliferation in mesangial cells, smooth muscle cells, and fibroblasts .

• Chemotactic effects: PDGF-D induces cell migration, particularly in fibroblasts and macrophages .

• Maturation of blood vessels: PDGF-D promotes pericyte/smooth muscle cell coating of blood vessels during angiogenesis .

• Regulation of interstitial fluid pressure: Transgenic mice expressing PDGF-D show elevated interstitial fluid pressure in the dermis .

• Adipocyte differentiation: PDGF-D appears to influence adipogenesis based on oil red O staining experiments in cell culture models .

These cellular effects are mediated through receptor-induced signaling cascades that involve receptor autophosphorylation and activation of downstream pathways.

How does PDGF-D interact with other growth factors during angiogenesis?

PDGF-D works cooperatively with other growth factors during angiogenesis. When co-expressed with vascular endothelial growth factor-E (VEGF-E), PDGF-D significantly enhances pericyte/smooth muscle cell recruitment to newly formed blood vessels . This interaction leads to increased maturation of VEGF-E-induced vessels and inhibits the vascular leakiness that typically accompanies VEGF-E-induced angiogenesis . The complementary roles of these growth factors highlight the complex coordination required for proper blood vessel formation: VEGF primarily stimulates endothelial cell proliferation and initial vessel formation, while PDGF-D promotes the recruitment of supporting cells necessary for vessel stabilization and maturation.

What is the role of PDGF-D in tissue repair and wound healing?

PDGF-D plays a significant role in tissue repair and wound healing processes. In transgenic mice expressing PDGF-D in basal epidermal cells, wound healing is characterized by increased cell density and enhanced recruitment of macrophages to the healing site . The macrophage recruitment function appears to be a consistent effect of PDGF-D, as similar responses were observed when PDGF-D was expressed in skeletal muscle or ear tissues using adeno-associated virus vectors . Beyond macrophage recruitment, PDGF-D likely contributes to wound healing through its mitogenic effects on fibroblasts and its role in supporting proper vascular remodeling during the repair process.

What is the role of PDGF-D in coronary artery disease risk?

PDGF-D has been implicated as a significant factor in coronary artery disease (CAD) risk through genome-wide association studies that identified the 11q22.3 locus containing the PDGF-D gene . Mechanistic studies have verified that the rs2019090 polymorphism at this locus affects PDGF-D expression, with the T allele associated with decreased FOXC1/C2 transcription factor binding and reduced PDGF-D expression . Bayesian hierarchical model analysis has demonstrated a significant relationship between CAD GWAS meta-analysis data and vascular tissue expression data for PDGF-D . The genetic evidence is supported by functional studies showing that PDGF-D influences vascular smooth muscle cell behavior, potentially contributing to the development of atherosclerotic lesions through effects on cell proliferation, migration, and vascular remodeling.

How does PDGF-D contribute to kidney disease progression?

PDGF-D acts as a potent mesangial cell mitogen and contributes significantly to kidney disease progression . In mouse models with adenovirus-mediated overexpression of PDGF-D, animals developed severe mesangial proliferative glomerulopathy characterized by enlarged glomeruli and dramatically increased glomerular cellularity . This pathological response was more severe than that observed with PDGF-B overexpression, while PDGF-C overexpression showed no measurable response . In quantitative terms, mice overexpressing PDGF-B showed a mild increase in glomerular size (4343.5 μm²) and number of cells per glomerular tuft (78), while PDGF-D-expressing mice exhibited more dramatic changes . These findings suggest that PDGF-D signaling represents a potential therapeutic target for mesangial proliferative kidney diseases.

What evidence links PDGF-D to cancer progression, particularly in prostate cancer?

Multiple lines of evidence support PDGF-D's role in cancer progression, with particularly strong data for prostate cancer :

• Autocrine signaling: LNCaP prostate cancer cells can auto-activate latent PDGF-D, which induces phosphorylation of the β-PDGF receptor and stimulates cell proliferation in an autocrine manner .

• Paracrine effects: LNCaP-PDGF-D-conditioned medium induces migration of prostate fibroblast cell line 1532-FTX, indicating PDGF-D also functions in a paracrine manner to influence stromal cells .

• In vivo tumor growth: In a severe combined immunodeficient mouse model, PDGF-D expression accelerates early onset of prostate tumor growth and dramatically enhances prostate carcinoma cell interaction with surrounding stromal cells .

These findings demonstrate PDGF-D's potential oncogenic activity in prostate cancer through both direct effects on cancer cells and modulation of tumor-stromal interactions that support cancer progression.

What animal models are available for studying PDGF-D function?

Several animal models have been developed to study PDGF-D function in vivo:

• Transgenic mice expressing PDGF-D in basal epidermal cells: These mice exhibit increased macrophage numbers and elevated interstitial fluid pressure in the dermis, making them valuable for studying PDGF-D's role in skin biology and wound healing .

• Adenovirus-mediated PDGF-D delivery models: These models allow for controlled, time-limited expression of PDGF-D in specific tissues and have been particularly useful for studying renal pathology, showing that PDGF-D induces severe mesangial proliferative glomerulopathy .

• AAV vector models with tissue-specific promoters: AAV vectors carrying PDGF-D under the control of the RPE-specific VDM2 promoter have been used to study PDGF-D function in retinal tissues .

• Xenograft models with PDGF-D-expressing cancer cells: Severe combined immunodeficient mice implanted with PDGF-D-expressing LNCaP cells have helped elucidate PDGF-D's role in prostate cancer progression .

These diverse models allow researchers to investigate PDGF-D function in different physiological and pathological contexts.

What techniques can be used to measure PDGF-D expression and activity?

Multiple techniques are available for assessing PDGF-D expression and activity:

• Gene expression analysis:

  • Quantitative real-time PCR for mRNA expression levels using the 2^(-ΔΔCT) method with appropriate reference genes like β-actin

  • RNA sequencing for genome-wide expression analysis

• Protein detection:

  • Western blotting with specific antibodies for PDGF-D protein quantification

  • Immunofluorescence for visualizing tissue localization of PDGF-D expression

• Functional assays:

  • PDGF receptor phosphorylation assays to measure activation of downstream signaling

  • Cell proliferation assays to assess mitogenic activity

  • Migration assays for chemotactic effects

  • Oil Red O staining for effects on adipocyte differentiation

• In vivo assessment:

  • Histological examination of affected tissues with quantitative morphometric analysis

  • Measurement of interstitial fluid pressure

  • Analysis of cell recruitment (particularly macrophages) to tissues

These complementary approaches provide a comprehensive assessment of PDGF-D expression, processing, and biological activity.

How can researchers effectively manipulate PDGF-D signaling pathways?

Researchers can manipulate PDGF-D signaling through several approaches:

• Genetic manipulation of PDGF-D expression:

  • Overexpression using viral vectors (lentivirus, adenovirus, AAV)

  • Gene silencing via CRISPRi with dCas9KRAB and specific guide RNAs

  • Traditional siRNA or shRNA approaches

• Receptor-level interventions:

  • PDGF receptor tyrosine kinase inhibitors

  • Receptor-neutralizing antibodies

  • Genetic manipulation of PDGFRA or PDGFRB expression

• Ligand-level interventions:

  • Recombinant PDGF-D protein administration

  • Anti-PDGF-D neutralizing antibodies

  • Inhibition of proteases responsible for PDGF-D activation

• Downstream signaling manipulation:

  • Pharmacological inhibitors of key signaling nodes

  • Genetic manipulation of downstream effectors

When designing interventions, researchers should consider cell type-specific responses, compensatory mechanisms, and potential roles of PDGF receptor heterodimers or crosstalks with other signaling pathways.

How do tissue-specific proteases regulate PDGF-D activation in different pathological contexts?

While we know PDGF-D requires proteolytic processing for activation, the specific proteases involved in different tissues and disease states remain incompletely characterized . Future research should focus on identifying these proteases and their regulation in various contexts, particularly in cancer and inflammatory conditions. Methodological approaches might include protease inhibitor screens, proteomics analysis of PDGF-D-associated proteins, and targeted gene editing of candidate proteases. Understanding tissue-specific activation mechanisms could reveal new therapeutic targets for modulating PDGF-D activity in a context-dependent manner.

How might targeted PDGF-D therapies be developed for mesangial proliferative kidney diseases?

Given PDGF-D's potent effects on mesangial cell proliferation and its role in glomerular pathology , developing targeted therapies for mesangial proliferative diseases represents an important research direction. Future investigations should explore:

• Delivery methods for kidney-specific PDGF-D inhibition

• Development of antibodies or small molecules that selectively inhibit PDGF-D without affecting other PDGF family members

• Identification of downstream mediators unique to PDGF-D signaling in mesangial cells

• Combination therapies targeting both PDGF-D and complementary pathways