Fig 2: Activation of the DNA Damage Response (DDR) pathway. (A) Immunofluorescence panels showing expression of phospho-H2AFX, a marker for the double-stranded DNA breaks (DSBs) in the myocardial sections. (B) Quantitative data showing the percentage of nuclei staining positive for the expression of pH2AFX. (C) Immunofluorescence panels showing expression of phospho-H2AFX in isolated cardiac fibroblasts. Panels representing the expression of pH2AFX (green color), PDGFRA (red), and the overlay are presented along with enlarged inserts showing the expression of pH2AFX in the nuclei of isolated cardiac fibroblasts. (D) Graph depicting the percentage of the cells co-expressing PDGFRA and pH2AFX in the experimental and control groups. (E) Immunoblots showing expression of selected proteins involved in the DDR pathways, namely pH2AFX, total H2AFX, ATN, and CGAS, along with blot representing controls for the loading conditions, are shown in the WT, Pdgfra-Cre, Pdgfra-Cre:LmnaW/F, and Pdgfra-Cre:LmnaW/F mice. (F) Quantitative data corresponding to the blots shown in panel C.

Fig 3: Expression of senescence markers. (A) Immunoblots showing levels of phospho-TP53 S18 and S389 proteins as well as the bonafide downstream target of activation of TP53, namely CDKN1A, in the experimental groups. (B) Quantitative data representing the blots shown in panel A. (C) Thin myocardial sections were stained for the expression of senescence-associated ß-galactosidase, detecting its expression in the heart of 6-week-old Pdgfra-Cre:LmnaF/F mice. (D) Immunoblots showing increased expression levels of CTGF (CCN2) and LGALS3, SASP markers, in the Pdgfra-Cre:LmnaF/F mouse hearts. Quantitative data are shown in panels (E and F). (G) Transcript levels of selected senescence-associated secretory phenotype (SASP), quantified by RT-PCR, showing increased transcript levels in the Pdgfra-Cre:LmnaF/F mouse hearts, as compared to other genotypes.

Fig 4: Myocardial fibrosis. (A) Representative images of Low (upper) and high (lower) magnification of thin myocardial sections stained for picrosirius red, which illustrates increased myocardial fibrosis in the Pdgfra-Cre:LmnaF/F mice at six weeks of age. (B) Quantitative data showing collagen volume fraction (CVF) in the experimental and control groups. (C) Immunoblot showing levels of latent and mature TGFß1 in the control and experimental groups, which were markedly increased in the Pdgfra-Cre:LmnaW/F and Pdgfra-Cre:LmnaF/F mice. (D) Quantitative data representing the blot in panel C. (E) Transcript levels of selected markers of myocardial fibrosis, quantified by RT-PCR, in the control and experimental groups. (F) Thin myocardial sections stained for picrosirius red in the Pdgfra-Cre:LmnaW/F and control mice, showing increased myocardial fibrosis. (G) Quantitative data showing increased CVF in the Pdgfra-Cre:LmnaW/F mouse myocardium as compared to the WT and Pdgfra-Cre mice at one year of age. (H) Transcript levels of selected markers of fibrosis, showing increased levels of selected markers but not Tgfb1 in the myocardium of one-year-old Pdgfra-Cre:LmnaW/F mice.

Fig 5: PDGFRA defines the mesenchymal stem cell Kaposi’s sarcoma progenitors by enabling KSHV oncogenesis in an angiogenic environment.Model showing PDGFRA(+)/SCA-1(+) bone marrow-derived mesenchymal stem cells (Pa(+)S MSCs) as KS spindle-cell progenitors. Pro-angiogenic environmental conditions typical of KS (KS-like media), inflammation and wound healing are critical for KSHV sarcomagenesis. This is because growth in KS-like conditions generates a de-repressed KSHV epigenome allowing oncogenic KSHV gene expression in infected Pa(+)S MSCs. Furthermore, these growth conditions allow KSHV-infected Pa(+)S MSCs to overcome KSHV-driven oncogene-induced senescence and cell cycle arrest via a PDGFRA-signaling mechanism; thus identifying PDGFRA not only as a phenotypic determinant for KS-progenitors but also as a critical enabler for viral oncogenesis.