Mechanical strain induces involution-associated events in mammary epithelial cells

Ana Quaglino,Edith C Kordon,Marcelo Salierno,Natalia Rubinstein,Jesica Pellegrotti

doi:10.1186/1471-2121-10-55

Abstract

BackgroundShortly after weaning, a complex multi-step process that leads to massive epithelial apoptosis is triggered by tissue local factors in the mouse mammary gland. Several reports have demonstrated the relevance of mechanical stress to induce adaptive responses in different cell types. Interestingly, these signaling pathways also participate in mammary gland involution. Then, it has been suggested that cell stretching caused by milk accumulation after weaning might be the first stimulus that initiates the complete remodeling of the mammary gland. However, no previous report has demonstrated the impact of mechanical stress on mammary cell physiology. To address this issue, we have designed a new practical device that allowed us to evaluate the effects of radial stretching on mammary epithelial cells in culture.ResultsWe have designed and built a new device to analyze the biological consequences of applying mechanical stress to cells cultured on flexible silicone membranes. Subsequently, a geometrical model that predicted the percentage of radial strain applied to the elastic substrate was developed. By microscopic image analysis, the adjustment of these calculations to the actual strain exerted on the attached cells was verified. The studies described herein were all performed in the HC11 non-tumorigenic mammary epithelial cell line, which was originated from a pregnant BALB/c mouse. In these cells, as previously observed in other tissue types, mechanical stress induced ERK1/2 phosphorylation and c-Fos mRNA and protein expression. In addition, we found that mammary cell stretching triggered involution associated cellular events as Leukemia Inhibitory Factor (LIF) expression induction, STAT3 activation and AKT phosphorylation inhibition.ConclusionHere, we show for the first time, that mechanical strain is able to induce weaning-associated events in cultured mammary epithelial cells. These results were obtained using a new practical and affordable device specifically designed for such a purpose. We believe that our results indicate the relevance of mechanical stress among the early post-lactation events that lead to mammary gland involution.

Highlights

After weaning, a complex multi-step process that leads to massive epithelial apoptosis is triggered by tissue local factors in the mouse mammary gland
Using this device we observed that radial cell stretching modified the expression and/or activation of c-Fos, ERK1/2, AKT, STAT3 and Leukemia Inhibitory Factor (LIF), which are involved in mammary regression after weaning
In order to predict the percentage of radial strain applied (RSA) to the elastic substrate, we have developed a theoretical model based on the device geometry

Summary

Introduction

A complex multi-step process that leads to massive epithelial apoptosis is triggered by tissue local factors in the mouse mammary gland. It has been proposed that milk accumulation, caused by the lack of suckling, might subject alveolar cells to mechanical strain This stress could be, per se, the earliest stimulus to trigger expression and release of local factors that would initiate mammary gland involution [11]. To address this question, we developed a new device, inspired in a system previously described by Lee and coworkers [12], which allowed us to exert up to 30% radial strain to non-tumorigenic mammary epithelial cells (HC11). These results confirmed that mechanical stress could be the very first initiator of post-lactational mammary gland involution

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