No abstract

Diet-induced obesity has been associated with various metabolic and reproductive disorders, including polycystic ovary syndrome. However, the mechanisms by which obesity influences the reproductive system are still not fully known. Studies have suggested that impairments in hormone signaling are associated with the development of symptoms such as acyclicity and ovarian cysts. However, these studies have often failed to address how these hormonal changes arise and how they might contribute to the progression of reproductive diseases. In the present study, we used a high-fat, high-sugar (HFHS) diet to induce obesity in a female rodent model to determine the changes in critical reproductive hormones that might contribute to the development of irregular estrous cycling and reproductive cycle termination. The HFHS animals exhibited impaired estradiol, progesterone (P4), and luteinizing hormone (LH) surges before ovulation. The HFHS diet also resulted in altered basal levels of testosterone (T) and LH. Furthermore, alterations in the basal P4/T ratio correlated strongly with ovarian cyst formation in HFHS rats. Thus, this model provides a method to assess the underlying etiology of obesity-related reproductive dysfunction and to examine an acyclic reproductive phenotype as it develops.

Restraint stress is a psychosocial stressor that suppresses reproductive status, including LH pulsatile secretion, but the neuroendocrine mechamisms underlying this inhibition remains unclear. Reproductive neural populations upstream of gonadotropin releasing hormone (GnRH) neurons, such as kisspeptin, neurokinin B, and RFRP-3 (GnIH) neurons, are possible targets for psychosocial stress to inhibit LH pulses, but this has not been well-examined, especially in mice in which prior technical limitations prevented assessment of in vivo LH pulse secretion dynamics. Here we examined whether one-time acute restraint stress alters in vivo LH pulsatility and reproductive neural populations in male mice, and what the time-course is for such alterations. We found that endogenous LH pulses in castrated male mice are robustly and rapidly suppressed by one-time, acute restraint stress, with suppression observed as quickly as 12–18 min. This rapid LH suppression parallels with increased in vivo corticosterone levels within 15 min of restraint stress. Although Kiss1, Tac2, and Rfrp gene expression in the hypothalamus did not significantly change after 90 or 180 min restraint stress, arcuate Kiss1 neural activation was sigmnifciantly decreased after 180 min. Interestingly, hypothalamic Rfrp neuronal activation was strongly increased at early times after restraint stress initiation, but was attenuated to levels lower than controls by 180 min of restraint stress. Thus, the male neuroendocrine reproductive axis is quite sensitive to short-term stress exposure, with significantly decreased pulsatile LH secretion and increased hypothalamic Rfrp neuronal activation occurring rapidly, within minutes, and decreased Kiss1 neuronal activation also occurring after longer stress durations.

BackgroundNeuroinflammation and microglial activation are critical components of Alzheimer’s Disease neuropathology as observed in patients and animal models. Microglia have multiple functions in addition to their inflammatory phenotype that can contribute to disease. Specifically, iron accumulates in AD‐associated brain regions, and we and others have shown enhanced iron load in activated microglia surrounding amyloid‐beta (Aβ) plaques. Furthermore, we and others have shown a distinct upregulation in the microglial iron importer, divalent metal transporter 1 (DMT1) in response to Aβ. Our aim is to further elucidate the role of microglial iron‐handling in age and AD‐associated inflammation.MethodWe measured DMT1 gene expression to assess changes in iron‐handling in response to age and inflammation. Microglia isolated from aged mice were treated with an inflammatory Aβ stimulus before measuring DMT1 expression and immunohistochemical markers of iron load. To determine the role of microglial DMT1 during inflammatory pathology in vivo, we targeted DMT1 expression utilizing a microglial‐specific tamoxifen‐inducible genetic mouse model in males and females. Transgenic mice were given intraperitoneal lipopolysaccharide (LPS) as a widely‐used model of neuroinflammation. We isolated microglia 24hr after LPS administration and measured DMT1 expression via qRT‐PCR for knockdown confirmation. Sickness behavior and markers of inflammatory state were also assessed.ResultMicroglia from 2‐year‐old aged mice display an augmented increase in Aβ‐induced DMT1 expression compared to young controls. Our in vivo studies also suggest a sex‐dependent increase in microglial DMT1 expression following systemic LPS. In our genetic mouse model, we obtained a 79% and 89% knockdown of microglial DMT1 gene expression in males and females, respectively. Male knockdown animals exhibited a trending decrease in Il‐1β expression in response to LPS, indicating an intimate link between pro‐inflammatory signaling and microglial iron‐handling.ConclusionThese studies link changes in microglial iron‐handling and the neuroinflammatory response. Additional in vivo work is further being analyzed to comprehensively determine the effects of DMT1 inhibition on the neuroinflammatory response. Considering the prominence of iron‐loaded microglia and chronic neuroinflammation in late‐stage AD, early intervention aimed at a specific aspect of microglial iron‐handling could be a target to decrease inflammation and AD‐related pathology.