Investigação da participação da via WNT no reparo ósseo em camundongos e a influência da Diabetes Mellitus tipo 1 no reparo e remodelação óssea

Abstract

Bone is a dynamic tissue able to repair spontaneously after an injury of establishment of a defect, due to the coordinated action of matrix and bone cells, mediated by the activation of several signaling pathways. Some factors, such as diabetes, interfere on this biological response, resulting in a negative impact over bone repair and remodeling. Nevertheless, the mechanism involved are yet to be clarified. The present study aimed to investigate the role of Wnt/ß-catenin on bone repair in animals either normal or diabetic and study the effects of diabetes on the remodeling process. First of all, the study aimed to evaluate the role of Wnt pathway through the inhibition of Dkk-1 expression, a regulatory protein of this pathway. For this, it was used C57BL/6 mice submitted to 2 types of Dkk-1 deletion: global deletion (Dkk-1fl/fl;Rosa26ERT2:Cre) or osteocyte-specific deletion (Dkk-1fl/fl;Dmp1:Cre). Animals without deletion were used as control (Cre-negative). All animals were submitted to subcritical calvaria defect of 1.8 mm diameter. The animals were followed for 4 weeks after the surgical procedure and then euthanized. Calvaria bones were collected for microtomographic, histological and histometric analyses. And for investigation of the expression of gene involved on bone metabolism (Dkk-1; Runx2; OCN; OPG e RANKL). Blood samples were collected before euthanasia in order to determine serum levels of P1NP and CTx, biochemical markers of bone remodeling. In both strains, it was observed greater bone repair when (Dkk1fl/fl;Rosa26ERT2:Cre=33%; Dkk-1fl/fl;Dmp1:Cre=45%) compared to its respective control Cre-. However, only in the animals Dkk-1fl/fl;Dmp1:Cre+ it was observed an increase of P1NP, a marker of bone formation and reduction of CTx, marker of bone resorption. Deletion of osteocyte-derived Dkk-1 significantly increased the amount of mineralized bone surface, mineral apposition rate and bone formation, as well as the number of osteoblasts. Considering the genetic expression, in Dkk-1fl/fl;Dmp1:Cre+ there was an increase of Runx2, OCN e OPG. Therefore, we can conclude that Wnt plays a role on bone repair and the use of animals with specific deletion of osteocytederived Dkk-1 is a potential research tool to study the involvement of Wnt pathway on bone metabolism, in several pathological conditions associated. On the second part of this study, C57BL/6 mice with specific deletion of Dkk-1 in osteocytes (Dkk1fl/fl;Dmp1:Cre) were subjected to the model of type 1 diabetes (T1DM) using 5 consecutive injections of streptozotocin (STZ) (40 mg/kg – i.p) aiming to evaluate the 13 impact of T1DM on bone repair. The respective offspring cre-negative animals were used as control. Twelve weeks later, the animals were subjected to the model of calvaria defect as described previously. After euthanasia, 4 weeks after the surgical procedure, calvaria and femur from each animal were collected for microtomographic, histological and histometric analyses. Blood samples were collected in order to determine serum levels of proteins involved with bone metabolism. Corporal weight and the amount of perigonodal and subcutaneous fats were analyzed. T1DM reduced by 46% the volume of trabecular bone in animals Cre- , while the Dkk-1 knockout animals lost only 16%. The cortical bone loss was completely protected in diabetic Dkk-1 knockout animals. T1DM suppressed the bone formation rate, number of osteoblast, the serum levels of P1NP and bone defect repair in either Cre- or Cre+ animals. The number of osteoclasts and the serum levels of TRAP were increased only in diabetic control animals. In summary, osteocyte-derived Dkk-1 does not interfere on the development of T1DM, and it does not mediate bone repair during T1DM, but it plays an important role on bone loss induced by osteocyte-derived Dkk-1 by regulation of osteoclasts.