Histidine dipeptides are key regulators of excitation-contraction coupling in cardiac muscle: Evidence from a novel CARNS1 knockout rat model.

Histidine-containing dipeptides (HCDs) are abundantly expressed in striated muscles. Although important properties have been ascribed to HCDs, including H+ buffering, regulation of Ca2+ transients and protection against oxidative stress, it remains unknown whether they play relevant functions in vivo. To investigate the in vivo roles of HCDs, we developed the first carnosine synthase knockout (CARNS1-/-) rat strain to investigate the impact of an absence of HCDs on skeletal and cardiac muscle function. Male wild-type (WT) and knockout rats (4 months-old) were used. Skeletal muscle function was assessed by an exercise tolerance test, contractile function in situ and muscle buffering capacity in vitro. Cardiac function was assessed in vivo by echocardiography and cardiac electrical activity by electrocardiography. Cardiomyocyte contractile function was assessed in isolated cardiomyocytes by measuring sarcomere contractility, along with the determination of Ca2+ transient. Markers of oxidative stress, mitochondrial function and expression of proteins were also evaluated in cardiac muscle. Animals were supplemented with carnosine (1.8% in drinking water for 12 weeks) in an attempt to rescue tissue HCDs levels and function. CARNS1-/- resulted in the complete absence of carnosine and anserine, but it did not affect exercise capacity, skeletal muscle force production, fatigability or buffering capacity in vitro, indicating that these are not essential for pH regulation and function in skeletal muscle. In cardiac muscle, however, CARNS1-/- resulted in a significant impairment of contractile function, which was confirmed both in vivo and ex vivo in isolated sarcomeres. Impaired systolic and diastolic dysfunction were accompanied by reduced intracellular Ca2+ peaks and slowed Ca2+ removal, but not by increased markers of oxidative stress or impaired mitochondrial respiration. No relevant increases in muscle carnosine content were observed after carnosine supplementation. Results show that a primary function of HCDs in cardiac muscle is the regulation of Ca2+ handling and excitation-contraction coupling.

Expression of angiogenic factors in placenta of stressed rats.

The aim of the present study was to analyse the influence of stress on pregnant rats, particularly in terms of maternal, placental and fetal weight, placental morphology and placental gene expression of the angiogenic factors Vegfa and Pgf and their receptors. The parameters were evaluated on gestation Day 20. Maternal, fetal and placental weights were statistically lower in stressed animals than controls, suggesting abnormalities in gestational physiology. Morphologically the placentas of rats subjected to stress were reduced in size and weight, with few glycogen cells and a significant increase in the number of apoptotic cells. Stress caused an increase in placental gene expression of Vegfa (P<0.05) and a reduction in Pgf, Flt1 and Kdr expression (P<0.05). It has been suggested that increased VEGF is associated with vasodilatation and hypotension, but in this model persistent hypertension was present. This study suggests that the limited hypotensive Vegfa response to stress-induced hypertension could result from reduced expression of Flt1/Kdr disrupting specific VEGF pathways. These findings may elucidate one of the multiple possible factors underlying how stress modulates placental physiology, and could aid the understanding of stress-induced gestational disorders.

Expressão gênica de fatores angiogênicos na placenta de ratas submetidas ao estresse / Expression of the angiogenic factors in the placenta of stressed rats

Objetivos: Avaliar a influencia do estresse sobre os pesos maternos, placentários e fetais, as alterações histológicas placentárias e a expressão gênica dos fatores angiogênicos em ratas prenhes. Métodos: De setembro de 2007 a julho de 2008, foi realizado um estudo experimental do tipo casocontrole, em que 6 ratas prenhes foram submetidas a estímulos estressantes crônicos e agudos enquanto que 6 animais constituíram o grupo controle. No 20º dia de prenhez, todas as ratas foram sacrificadas. Os seguintes dados foram analisados e comparados entre os grupos: a. pesos maternos, placentários e fetais; b. alterações histológicas placentárias; e, c. expressão gênica dos fatores angiogênicos (VEGF-A e PlGF), dos seus receptores (VEGFR-1 e VEGFR-2) e do fator induzido por hipoxia (HIF-1). Resultados: Os pesos maternos, placentários e fetais foram significativamente menores no grupo de ratas prenhes-estressadas em relação ao controle. Histologicamente foram encontradas a presença de núcleos picnóticos no grupo prenhe-estressado. Observou-se expressão gênica significativamente maior de VEGF-A no grupo rata prenhe-estressada assim como redução significante da expressão gênica de PlGF, VEGFR-1, VEGFR-2, quando comparadas ao controle. Não houve alterações entre os grupos para o gene HIF-1. Conclusões: No modelo animal de estresse estudado, observou-se alterações significativas no peso placentário e da expressão gênica dos fatores angiogênicos placentários em ratas submetidas ao estresse.

Objectives: to evaluate the influence of the stress on the maternal, placental and fetal weights, on the histological findings and on the genetic expression of the angiogenic factors in pregnant rats. Methods: From September 2007 to Julie 2008, an experimental case-control study was conduced in which 6 pregnant rats were submitted to chronic and acute stress while six other were considered as controls. In the 20th day of gestation, all animals were sacrified. The following data were evaluated and compared between both groups: a. maternal, placental and fetal weights; b. histological findings; and c. genetic expression of angiogenic factors (VEGF-A and PIGF), receptors (VEGFR-1 and VEGFR-2) and hypoxic-induced factor (HIF- 1). Results: Maternal, placental and fetal weights were statistically smaller in the stressed animals comparing to controls. Histological analysis revealed picnotic nuclei in the placentas of stressed rats. A statistically significant increase in the genetic expression of VEGF-A as well as a reduction of the expression of the PlGF, VEGFR-1, VEGFR-2 were observed in the placentas of the stressed group in comparison to controls. There was no difference of expression of the gene HIF-1 between both groups. Conclusions: In the present animal model of stress, significant alterations in the placental weights, histology and genetic expression of the angiogenic factors among pregnant rats under stress.