Angiotensin II (Ang II) promotes vascular disease and hypertension, in part, by activating the interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) signaling pathway. Extensive studies have demonstrated that SOCS3 plays an important role in suppressing the IL-6/STAT3 pathway in the immune system and in cancer biology. In contrast, the functional importance of SOCS3 in cardiovascular disease is largely unknown. Thus, the overall goal of these studies was to investigate the role of SOCS3 in models of Ang II-dependent vascular disease and hypertension. To examine direct effects of Ang II on the vessel wall, carotid arteries from SOCS3 haplodeficient (SOCS3+/-) mice and wild-type littermates (SOCS3+/+) were incubated with the peptide or vehicle for 22 hrs, followed by examination of endothelial function using acetylcholine. Relaxation to acetylcholine was similar in all arteries incubated with vehicle. A low concentration of Ang II (1 nmol/L) did not affect acetylcholine-induced vasodilation in SOCS3+/+ mice, but reduced responses in arteries from SOCS3+/- mice by ~50% (P<0.05). This Ang II-induced endothelial dysfunction in SOCS3+/- mice was prevented by inhibitors of NF-êB or STAT3, an IL-6 neutralizing antibody, or a scavenger of superoxide. Responses to nitroprusside, an endothelium-independent vasodilator, were similar in all groups. To test the importance of SOCS3 in vivo, mice were infused systemically with a pressor dose of Ang II (1.4 mg/kg per day) or vehicle for 14 days via osmotic mini-pumps. Acetylcholine-induced vasodilation in carotid and resistance arteries in brain from SOCS3+/- mice was reduced by ~60% (P<0.05). Surprisingly, genetic deficiency in SOCS3 prevented the majority of Ang II-induced endothelial dysfunction without affecting the pressor response to Ang II. To investigate potential mechanisms underlying divergent results when studying effects of local versus systemic effects of Ang II, we performed bone marrow transplantation followed by infusion of vehicle or Ang II for two weeks. Lethally irradiated WT (CD45.1) mice reconstituted with SOCS3+/- bone marrow were protected from Ang II-induced endothelial dysfunction (P<0.05), while reconstitution of irradiated SOCS3+/- mice with WT (CD45.1) bone marrow exacerbated Ang II-induced vascular dysfunction (P<0.05). WT (CD45.1) into SOCS3+/+ and SOCS3+/- into SOCS3+/- bone marrow chimeras exhibited vascular function consistent with non-irradiated controls. In addition, the pressor response to Ang II was reduced by ~50% in WT mice reconstituted with bone marrow from SOCS3+/- mice (P<0.05). These data suggest that SOCS3 exerts divergent or context-dependent effects depending on whether vascular dysfunction was due to local versus systemic administration of Ang II. SOCS3 deficiency in the vessel wall enhanced local detrimental effects of Ang II on vascular function. In contrast, bone marrow-derived cells that are haplodeficient in SOCS3 protect against systemically administered Ang II and the resulting vascular dysfunction and hypertension. To my knowledge, these are the first experimental studies that begin to define the importance of SOCS3 in Ang II-induced hypertension and endothelial dysfunction. Results obtained from these experiments provide new insight into mechanisms which regulate oxidative stress and inflammation within the vasculature. The studies also revealed that bone marrow-derived cells that are haplodeficient in SOCS3 protect against pressor and endothelial effects of Ang II. These findings may eventually contribute to the development of novel therapeutic approaches for hypertension and hypertension associated end-organ damage.

Pulmonary arterial hypertension (PAH) is a rare, devastating disease with no cure. Current treatment consists of a cocktail of vasodilators which relieve symptoms of PAH but do not treat the cause. Thus, there is a need for novel drugs that target the underlying pathological causes of PAH. PAH is a multi-factorial, but one key contributor is the pro-inflammatory cytokine IL-6 which stimulates pro-inflammatory and pro-angiogenic signalling mediated by the JAK/STAT pathway. One way in which IL-6 signalling via JAK/STAT is inhibited is via SOCS3 in a type of negative feedback loop whereby IL-6 induces transcription of SOCS3, which then attenuates further JAK/STAT signalling. SOCS3 can also be induced by cAMP. This is interesting as prostanoids, a type of drug used in the treatment of PAH due to its vasodilator effects and the only type to show any efficacy improving the life expectancy of PAH patients, acts by mobilising cAMP. Thus, prostanoid stimulation of cAMP could potentially limit IL-6 signalling via the induction of SOCS3. This is a novel mechanism of prostanoids which has not previously been considered. This study investigated the capability of prostanoids to limit the pro-inflammatory/pro-angiogenic effects of IL-6 that enable PAH to develop. Initial experiments confirmed that vascular endothelial cells responded to prostanoids which increased SOCS3 and limited IL-6 signalling activity. Further experiments utilising SOCS3 KO endothelial cell models demonstrated prostanoid inhibition of IL-6 signalling was due in part to SOCS3. In conclusion, this project has confirmed that prostanoids do limit the pro-inflammatory effects induced by IL-6 and that this is in part due to SOCS3. Although the exact mechanism is yet to be discovered, it will be beneficial in the treatment of PAH as it provides currently unexploited drug targets which can be considered for future PAH therapies. / British Heart Foundation