Stress-Induced Suppression of Milk Protein Is Involved in a Noradrenergic Mechanism in the Mammary Gland

Abstract

Stress decreases milk components such as milk protein and milk yield. The objective of this study was to investigate whether noradrenaline (NA) in milk constituted a factor associated with stress-induced changes in milk proteins such as β-casein. Breast milk obtained from eight healthy, nursing women contained NA at concentrations ranging from 12.7 to 115.5 nM. The expression of tyrosine hydroxylase (TH), a rate-limiting enzyme of NA synthesis, was observed in primary normal human mammary epithelial cells (HMECs), and in MCF-12A and MCF-10A cell lines. The mean NA concentration in culture medium used by MCF-12A transfected with TH small interfering RNA (siRNA) was significantly lower than that of cells transfected with control siRNA. NA concentration in milk in restraint-stressed nursing mice was significantly higher than that in nonstressed nursing mice, owing to elevated TH expression in the mammary epithelium. The mean β-casein concentration in milk in restraint-stressed mice was significantly lower than that in nonstressed mice. NA treatment resulted in a concentration-dependent decrease in β-casein expression in HMECs. β2 adrenergic receptor (ADRB2) expression was observed in HMECs, MCF-12A, and MCF-10A, and immunohistochemical analysis of ADRB2 using mammary epithelium sections obtained from mice at day 10 of lactation showed that ADRB2 was expressed at the apical membrane of mammary epithelium. Treatment with salbutamol, an ADRB2 stimulant, decreased β-casein expression in a concentration-dependent manner in MCF-12A. Our results showed that endogenous NA derived from mammary epithelial cells likely comprises one of the factors involved in stress-induced changes in milk proteins such as β-casein.

β-Adrenoceptor Activation in Breast MCF-10A Cells Induces a Pattern of Catecholamine Production Similar to that of Tumorigenic MCF-7 Cells

“…Therefore, responses mediated by these catecholamines (including in tumorigenesis [32,33,38] have been solely associated with the activation of the SNS. The present study shows that breast cells can also synthesize catecholamines, confirming previous observations in normal human mammary epithelial cells [35], and in non-tumorigenic and tumorigenic breast cell lines [35,36].…”

“…In non-tumorigenic human breast cells, the main catecholamine produced was reported to be noradrenaline [35]. In the present study, in the tumorigenic MCF-7 cells, adrenaline was the main catecholamine detected in the conditioned medium, suggesting that the adrenaline/noradrenaline ratio may be seen as an index of tumorigenicity.…”

“…Noradrenaline and adrenaline are sequentially synthesized from tyrosine, and the conversion of tyrosine to L-DOPA, catalyzed by TH, is considered the rate-limiting step of catecholamine synthesis [39,40]. TH detection has been used to identify cells that synthesize catecholamines and the levels of TH expression as a way to estimate the potential of a given cell to produce catecholamines [35,36,41]. The present study shows that TH is expressed both in MCF-10A and MCF-7 breast cell lines.…”

“…Although tumors may recruit sympathetic adrenergic nerves [34], the possibility that tumor cells may also contribute to the catecholamine pool must also be considered. It was recently reported that human breast epithelial cells express tyrosine hydroxylase (TH; the rate-limiting enzyme of catecholamine synthesis) and produce noradrenaline, described as a putative mechanism for the stress-induced changes in milk composition [35]. Moreover, transfected breast tumorigenic cells (MCF-7 overexpressing Her-2) were also reported to produce catecholamines [36].…”

Milking it for all it’s worth: The effects of environmental enrichment on maternal nurturance, lactation quality, and offspring social behavior

“…For example, nursing mice fed a high-fat diet demonstrated an increase in milk lactose and fat content as well as differently expressed mRNAs related to central nervous system development (Chen et al, 2017). Restraint stress has been shown to reduce milk protein in lactating mice (Chiba et al, 2019) and other stressors such as social and heat stress have been shown to negatively affect lactation (Murgatroyd et al, 2015) and milk yield (Haldar & Bade, 1981) respectively. Such evidence underscores how the maternal environment may contribute to alterations in the nutritional profile of milk which may have subsequent consequences on progeny development, although effects on offspring remain largely unexplored.…”