Implications of the RhoA/Rho associated kinase pathway and leptin in primary uterine inertia in the dog

Abstract

The underlying functional and molecular changes in canine primary uterine inertia (PUI) are still not clarified. Leptin (Lep) and obesity negatively affect uterine contractility in women, partly mediated by the RhoA/Rho kinase pathway, affecting myometrial calcium sensitization. We hypothesized that increased uterine Lep/Lep receptor (LepR) or decreased RhoA/Rho kinase expression contributes to PUI in dogs, independent of obesity. Dogs presented for dystocia were grouped into PUI (n = 11) or obstructive dystocia (OD, still showing strong labor contractions; n = 7). Interplacental full-thickness uterine biopsies were collected during Cesarean section for relative gene expression (RGE) of RhoA, its effector kinases (ROCK1, ROCK2), Lep and LepR by qPCR. Protein and/or mRNA expression was evaluated by immunohistochemistry and in situ hybridization. RGE was compared between groups by one-way ANOVA using body weight as covariate with statistical significance P < 0.05. Uterine ROCK1 and ROCK2 gene expression was significantly higher in PUI than OD, while RhoA and Lep did not differ. LepR RGE was below the detection limit in 5 PUI and all OD dogs. Litter size had no influence. Lep, LepR, RhoA, ROCK1, ROCK2 protein and/or mRNA were localized in the myometrium and endometrium. Uterine protein expression appeared similar between groups. LepR mRNA signals appeared stronger in PUI than OD. In conclusion, lasting, strong labor contractions in OD resulted in downregulation of uterine ROCK1 and ROCK2, contrasting the higher expression in PUI dogs with insufficient contractions. The Lep-LepR system may affect uterine contractility in nonobese PUI dogs in a paracrine-autocrine manner.

Involvement of Oxytocin and Progesterone Receptor Expression in the Etiology of Canine Uterine Inertia

“…Furthermore, prolonged intracervical pressure, resulting in increased hypophyseal OXT release, could contribute to this desensitization. A decreased mRNA expression of other contractile and contractility associated proteins in IP sections of OD compared to PUI bitches has also been shown in our previous reports [ 16 , 17 ], corroborating the current findings and the proposed role of prolonged labor contractions on the uterus. Indeed, all OD bitches included in our study still showed strong straining as a response to digital vaginal feathering and spontaneous abdominal and/or uterine contractions, indicating that these bitches did not reach myometrial fatigue, causing secondary UI.…”

“…Despite the frequent occurrence of PUI in dogs and its severe consequences for maternal and offspring survival, the exact etiology is still unknown. Up to now, only few studies have investigated its pathophysiology from a molecular biology approach looking directly at the level of the uterus [ 16 , 17 , 32 , 45 , 46 ]. As both oxytocin and progesterone are crucial hormones during parturition, we hypothesized and identified altered expression of the respective receptors as potential causes for PUI.…”

“…The significantly higher OXTR mRNA expression (ratio) in IP samples obtained from PUI (and PUI-N) dams compared to OD might be a consequence of the absence of intracervical pressure due to the fact that no puppy had been born and, thus, having insufficient systemic OXT release, as previously postulated by Tamminen et al [ 32 ]. It is worth noting that comparison of the OD and PUI samples was shown to be suitable in previous studies to gain further insight into the pathophysiology of canine dystocia and specifically PUI [ 15 , 16 , 17 , 32 , 45 , 46 ].…”

“…The samples utilized in this study were already used previously by our research group [ 45 , 46 ] and our collaborators [ 15 , 16 , 17 ].…”

“…Nevertheless, predispositions have been described for several breeds [ 3 , 11 , 12 , 13 ] as well as risk factors, such as maternal overweight, advanced age, very small or large litter size, and hormonal, electrolyte, or metabolic imbalances [ 1 , 2 , 3 , 6 , 10 , 12 , 14 , 15 ]. Additionally, alterations in the expressions of basic contractile and contractility associated proteins in the uterus, e.g., smooth muscle γ-actin, smooth muscle myosin [ 16 ], the RhoA/Rho associated kinase pathway, and leptin signaling [ 17 ], were found in cases of PUI.…”