**3. Angiogenesis**

Angiogenesis is defined as the migration, development, and di fferentiation of endothelial cells to form new blood vessels [14]. It is initiated by pro-angiogenic vascular endothelial growth factors (VEGFs) and placental growth factors (PlGFs), which increase vessel permeability and promote proteolysis of the extracellular matrix via proteases, resulting in endothelial cell proliferation. Thereafter, endothelial cells migrate and invade the lumen, followed by endothelial maturation [15,16].

In normal pregnancy, the need for increased blood supply to the fetus is met by the physiological transformation of spiral arteries in both the decidua and myometrium. In contrast, as a result of deficient trophoblast invasion, spiral artery remodeling is restricted to the decidua in PE [17] and is often associated with adverse birth outcome.

Angiogenesis is also dysregulated in HIV-1 infected patients [18]. Notably, adverse birth outcome is elevated upon receipt of anti-retroviral therapy (ART) compared to HIV-uninfected women [19,20]. Since SA has the largest anti-retroviral rollout in the world, it is important to recognize any link(s) between HAART usage in pregnancy and the risk for PE development. In a novel study, Powis et al. (2013) assessed angiogenesis in preeclamptic women that initiated HAART during pregnancy [21]. They demonstrated that women who developed PE had an upregulation of anti-angiogenic factors prior to HAART usage. Moreover, a recent report correlated altered angiogenesis with ARV usage in the second and third trimesters as a progenitor of preterm birth, small for gestational age, and stillbirth [22].

#### *3.1. Soluble Fms-Like Tyrosine Kinase 1 (sFlt1), Placental Growth Factor (PlGF), and Soluble Endoglin (Eng)*

It is well documented that placental sFlt1 is elevated in PE, resulting in a rise in systemic levels with a concomitant decline in VEGF and PlGF [23]. The anti-angiogenic factor sFlt-1 is a scavenger receptor for VEGF and PlGF, thereby dampening their constructive e ffects on the maternal endothelium [24]. Moreover, in pregnan<sup>t</sup> rats, the administration of sFlt1 induces the clinical symptoms of PE [25]. Flt-1 and sFlt-1 levels in the placenta are upregulated in PE compared to controls, irrespective of HIV infection [26]. Working in our laboratory, Govender et al. (2013) demonstrated increasing

levels of serum sFlt1 and sEng in PE, regardless of HIV infection [27]. sFlt1 and sEng are implicated in the endothelial dysfunction of PE. Moreover the downregulation of serum sFlt1 and sEng within HIV-infected women advocates counterbalance of the immune hyperactivity in PE [27]. sEng weakens the binding of TGF-β1 to its receptors and blocks the activation of the endothelial nitric oxide synthase 3 (eNOS) pathways downstream, thereby inducing hypertension [28]. The recent use of sFlt-1:PlGF ratio for the clinical prediction of severe early-onset PE is encouraging [29].

### *3.2. Vascular Endothelial Growth Factor (VEGF)*

The permeability of blood vessels is enhanced by VEGF, thereby inducing angiogenesis and vasculogenesis [30]. The VEGF family comprises VEGF-A, VEGF-B, VEGF-C, VEGF-D, and PlGF [31]. VEGF receptors include VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1/KDR) [31]. VEGF-A and VEGF-B bind to VEGFR-1 (Flt-1); however, in PE, binding is blocked by the antagonist sFlt-1 or sVEGFR-1, a spliced soluble variant of VEGFR-1 [32]. VEGFR-2 is an antagonist to VEGF and increases arterial pressure [33]. Both VEGF-C and VEGF-D bind to VEGFR-3, thus expediting lymphangiogenesis [34].

#### *3.3. Platelet Endothelial Cell Adhesion Molecule* 1 (PECAM-1)

Vascular development is influenced by PECAM-1 through the formation of a complex with VEGFR-2 and VE cadherin [35]. In PE, PECAM-1 induces neutrophil and platelet activation, thereby promoting vascular damage [36]. Thakoordeen et al. (2017) demonstrated a similar level of PECAM-1 between control and preeclamptic pregnancies (*p* = 0.07), while no correlation was found based on HIV infection (*p* = 0.68) or across study groups (*p* = 0.24) [37].
