Interactions between vascular smooth muscle cells (VSMCs), endothelial cells (ECs), pericytes (PCs) and macrophages (MФ), the major components of blood vessels, play a crucial role in maintaining vascular structural and functional homeostasis. Low-density lipoprotein (LDL) receptor-related protein-1 (LRP1), a transmembrane receptor protein belonging to the LDL receptor family, plays multifunctional roles in maintaining endocytosis, homeostasis, and signal transduction. Accumulating evidence suggests that LRP1 modulates vascular homeostasis mainly by regulating vasoactive substances and specific intracellular signaling pathways, including the plasminogen activator inhibitor 1 (PAI-1) signaling pathway, platelet-derived growth factor (PDGF) signaling pathway, transforming growth factor-β (TGF-β) signaling pathway and vascular endothelial growth factor (VEGF) signaling pathway. The aim of the present review is to focus on recent advances in the discovery and mechanism of vascular homeostasis regulated by LRP1-dependent signaling pathways. These recent discoveries expand our understanding of the mechanisms controlling LRP1 as a target for studies on vascular complications.

The contribution of autophagy to catabolic balance has been well-established in various types of cells, whereas the involvement of autophagy in progesterone synthesis during rat pregnancy still remains unknown. Therefore, the present study was designed to evaluate the role of autophagy in progesterone production during the luteal development of pregnant rats. The results showed autophagy-related proteins was maintained at a low level on day 10 after pregnancy, significantly induced on day 16 and subsided to a relative low level on day 21, which was consistent with the changes of serum progesterone levels. The findings further indicated the contribution of autophagy to progesterone production was regulated by inactivation of Akt/mTOR signaling during the luteal development of pregnant rats in in vivo and in vitro experiments. Further investigations revealed autophagy may be involved in the surge of progesterone production in pregnant rats, as inhibition of autophagy by 3-MA compromised serum progesterone levels. Furthermore, 3-MA treatment also leveled down the number of lipid droplets in luteal cells, implying that autophagy may affect the production of progesterone by manipulating the formation of lipid droplets in luteal cells. In addition, the results suggested that mitophagy was mobilized during the primary stage of luteolysis and inhibition of autophagy promoted the increase of redundant mitochondrial and cytoplasmic cytochrome C in luteal cells of pregnant rats. Taken together, the present study indicated that autophagy-related proteins were induced by the inactivation of Akt/mTOR signaling and then contributed to the progesterone production possibly by affecting the formation of intracellular lipid droplets during the luteal development of pregnant rats. To our knowledge, this will provide a new insight into the important mechanism of autophagy regulating progesterone production in ovaries of pregnant mammals.

Testes produce sperms, and gamete generation relies on a proper niche environment. The disruption of hierarchical regulatory homeostasis in Leydig or Sertoli cells may evoke a sterile phenotype in humans. In this study, we recapitulated type 2 diabetes mellitus by using a high-fat diet- (HFD-) fed mouse model to identify the phenotype and potential mechanism of diabetes-induced testicular impairment. At the end of the study, blood glucose levels, testosterone structure, testicular antioxidant capacity, and testosterone level and the expression of hypoxia-inducible factor- (HIF-) 1α, apoptosis-related protein cleaved-caspase3, and autophagy-related proteins such as LC3I/II, p62, and Beclin1 were evaluated. We found that long-term HFD treatment causes the development of diabetes mellitus, implicating increased serum glucose level, cell apoptosis, and testicular atrophy ( vs. Ctrl). Mechanistically, the results showed enhanced expression of HIF-1α in both Sertoli and Leydig cells ( vs. Ctrl). Advanced glycation end products (AGEs) were demonstrated to be a potential factor leading to HIF-1α upregulation in both cell types. In Sertoli cells, high glucose treatment had minor effects on Sertoli cell autophagy. However, AGE treatment stagnated the autophagy flux and escalated cell apoptosis ( vs. Ctrl+Ctrl). In Leydig cells, high glucose treatment was adequate to encumber autophagy induction and enhance oxidative stress. Similarly, AGE treatment facilitated HIF-1α expression and hampered testosterone production ( vs. Ctrl+Ctrl). Overall, these findings highlight the dual effects of diabetes on autophagy regulation in Sertoli and Leydig cells while imposing oxidative stress in both cell types. Furthermore, the upregulation of HIF-1α, which could be triggered by AGE treatment, may negatively affect both cell types. Together, these findings will help us further understand the molecular mechanism of diabetes-induced autophagy dysregulation and testicular impairment, enriching the content of male reproductive biology in diabetic patients.

The increase of oxidative stress is one of the important characteristics of mammalian luteal regression. Previous investigations have revealed the essential role of reactive oxygen species (ROS) in luteal cell death during luteolysis, while it is unknown how ROS is regulated in this process. Considering the decrease of blood flow and increase of PGF_2α during luteolysis, we hypothesized that the HIF‐1α pathway may be involved in the regulation of ROS in the luteal cell of the late corpus luteum (CL). Here, by using a pseudopregnant rat model, we showed that the level of both HIF‐1α and its downstream BNIP3 was increased during luteal regression. Consistently, we observed the increase of autophagy level during luteolysis, which is regulated in a Beclin1‐independent manner. Comparing with early (Day 7 of pseudopregnancy) and middle CL (Day 14), the level of ROS was significantly increased in late CL, indicating the contribution of oxidative stress in luteolysis. Inhibition of HIF‐1α by echinomycin (Ech), a potent HIF‐1α inhibitor, ameliorated the upregulation of BNIP3 and NIX, as well as the induction of autophagy and the accumulation of ROS in luteal cells on Day 21 of pseudopregnancy. Morphologically, Ech treatment delayed the atrophy of the luteal structure at the late‐luteal stage. An in vitro study indicated that inhibition of HIF‐1α can also attenuate PGF_2α‐induced ROS and luteal cell apoptosis. Furthermore, the decrease of cell apoptosis can also be observed by ROS inhibition under PGF_2α treatment. Taken together, our results indicated that HIF‐1α signaling is involved in the regression of CL by modulating ROS production via orchestrating autophagy. Inhibition of HIF‐1α could obviously hamper the apoptosis of luteal cells and the process of luteal regression.

The maturation of testicular Leydig cells during the prepubertal stage is crucial for establishing male fertility. While diabetes is recognized as a significant detrimental factor affecting male testicular function, its impact specifically during the prepubertal period remains largely unknown. We hypothesized that prepubertal diabetes may impair testicular development by disrupting Leydig cell maturation. Using streptozotocin (STZ) administration, we established a prepubertal diabetic rat model and investigated the effects of diabetes on testicular development 2 and 4 weeks post-STZ treatment. Diabetes significantly hampered testicular development, manifesting as a decreased testicular weight, structural abnormalities, reduced testosterone levels, and increased inflammatory responses. As anticipated, prepubertal diabetes stagnated Leydig cell maturation and increased Leydig cell apoptosis. Mechanistic studies revealed that autophagy is essential for maintaining homeostasis and facilitating differentiation in immature Leydig cells but is significantly inhibited by hyperglycemia. Dysregulation of autophagy impaired the mitochondrial network, triggering inflammatory responses, suppressing steroidogenic capacity, and accumulating reactive oxygen species (ROS). Elevated ROS levels exacerbated the inflammatory response in the Leydig cells in an NLRP3-dependent manner. Inhibition of NLRP3 ameliorated the hyperglycemia-induced inflammation and decline in steroidogenic ability. Collectively, these findings demonstrate that hyperglycemia suppresses autophagy induction and enhances ROS accumulation in Leydig cells. This cascade promotes inflammation and inhibits steroidogenesis, thereby impeding testicular development in prepubertal diabetic rats.