Neonatal exposure to hypoxia induces early arterial stiffening via activation of lysyl oxidases.

Hypoxia in the neonatal period is associated with early manifestations of adverse cardiovascular health in adulthood including higher risk of hypertension and atherosclerosis. We hypothesize that this occurs due to activation of lysyl oxidases (LOXs) and the remodeling of the large conduit vessels, leading to early arterial stiffening. Newborn C57Bl/6 mice were exposed to hypoxia (FiO2  = 11.5%) from postnatal day 1 (P1) to postnatal day 11 (P11), followed by resumption of normoxia. Controls were maintained in normoxia. Using in vivo (pulse wave velocity; PWV) and ex vivo (tensile testing) arterial stiffness indexes, we determined that mice exposed to neonatal hypoxia had significantly higher arterial stiffness compared with normoxia controls by young adulthood (P60), and it increased further by P120. Echocardiography performed at P60 showed that mice exposed to hypoxia displayed a compensated dilated cardiomyopathy. Western blotting revelated that neonatal hypoxia accelerated age-related increase in LOXL2 protein expression in the aorta and elevated LOXL2 expression in the PA at P11 with a delayed decay toward normoxic controls. In the heart and lung, gene and protein expression of LOX/LOXL2 were upregulated at P11, with a delayed decay when compared to normoxic controls. Neonatal hypoxia results in a significant increase in arterial stiffness in early adulthood due to aberrant LOX/LOXL2 expression. This suggests an acceleration in the mechanical decline of the cardiovascular system, that contributes to increased risk of hypertension in young adults exposed to neonatal hypoxia that may increase susceptibility to further insults.

Targeting LOXL2 Improves Arterial Stiffness and Function in Angiotensin II-induced Hypertension in Males but not Females.

Background: Hypertension accelerates arterial stiffening associated with natural aging. Aortic stiffness is both a cause and a consequence of isolated systolic hypertension. We identified lysyl oxidase-like 2 (LOXL2), a key matrix remodeling enzyme, as a potential therapeutic target for treating vascular stiffening. Here, we determine if LOXL2 depletion is protective against hypertension induced arterial stiffening, and we elucidate the sex differences present. Methods: Angiotensin II (Ang II) pumps were implanted in Loxl2 +/- and WT mice. Blood pressure and pulse wave velocity were measured noninvasively to assess hypertension and aortic stiffness. Wire myography and uniaxial tensile testing were used to test aortic vasoreactivity and elastic properties. Histological analysis and Western blotting determined vascular wall properties. The effect of biomechanical strain on LOXL2 expression and cell alignment was determined via uniaxial cell stretching. Results: Ang II infusion induced hypertension in WT and Loxl2 +/- mice, and arterial stiffening was ameliorated in Loxl2 +/- male mice. LOXL2 depletion protected males from Ang II mediated potentiation of vasoconstriction, and attenuated passive arterial stiffening. Histological analysis showed increased aortic wall thickness and intralamellar distance with Ang II. Western blotting revealed an increase of LOXL2 accumulation and processing in hypertensive mice. Increased cyclic strain contributed to upregulation of LOXL2 in the aorta with induced hypertension. Conclusions: Arterial stiffening is increased with Ang II infusion; however, it is ameliorated in Loxl2 +/- male mice compared to WT despite developing Ang II-induced hypertension. This rise in arterial stiffness is driven by both VSMC response and matrix remodeling.