6 research outputs found
Secreted semaphorin signaling regulates aging-associated dendritic modifications and cognitive function
No full textThe age-associated loss of neuronal dendritic complexity may account for the synaptic loss and cognitive decline seen in aged mammals, including humans. Identifying the molecular players involved in these changes is necessary to understand the causes of the neurological phenotypes of normal aging. Some of the molecules involved in dendritic morphogenesis are the class 3 secreted semaphorins and their signaling receptors. In development, semaphorin 3A (Sema3A) signals through its receptors Neuropilin-1/Plexin(Plxn)-A4 to induce dendritic elaboration in layer V cortical neurons, while Sema3F signals through Neuropilin-2/Plexin-A3 to induce spine pruning on the apical dendrite of the same neurons. Importantly, Sema3A and Sema3F and their receptors are also expressed in adult and aged mammalian cortices, but their role in age-associated dendritic remodeling is unclear. Thus, I wondered if the presence of these class 3 secreted semaphorins (Sema3s) in the aged brain might maintain their developmental roles in regulating and/or maintaining the dendritic arbor of cortical neurons in the aged animals. Therefore, my hypothesis is: Altered expression of secreted semaphorins and their receptors in the aging brain drives changes in cortical neuron dendritic morphology and cognition. To address this hypothesis, I first established an in vitro model of aging in order to manipulate the direct effects of Sema3A and Sema3F on dendritic elaboration of primary cortical neurons grown at different length of time (age) in culture, which is more difficult to execute in vivo. By growing mouse primary cortical neurons up to 30 days in vitro (DIV), I demonstrated that aging-associated β-galactosidase levels also increase with age in culture. Then using this in vitro aged-neuron model, I found that treating with either Sema3A or Sema3F induces significantly more dendritic branching at 5DIV and 15DIV, but not at 30DIV, at which only simultaneous treatment with both Sema3A and Sema3F increased dendritic branching, suggesting there are changes in the cellular response to semaphorins with age in culture.
Brain-Derived Neurotrophic Factor (BDNF) is another molecule known to increase dendritic branching and is also expressed in the mammalian cortex. BDNF gene therapy is currently being used as a treatment to build synapses and improve memory in patients of AD. Therefore, I wondered if BDNF and Sema3s might have crosstalk in their abilities to promote dendritic elaboration. I examined the effect of BDNF on dendritic branching at 5 and 30DIV and treated cultured neurons simultaneously with BDNF and Sema3A or Sema3F to test for any additive effects on dendritic branching. I found that BDNF alone was able to increase dendritic branching at both 5 and 30DIV, but that Sema3F suppressed BDNF-induced dendritic branching at both 5DIV and 30DIV. Sema3A suppressed BDNF-induced dendritic branching in more distal dendrites at 5DIV, but increased perisomatic dendritic branching compared to the BDNF single treatment at 30DIV. These results suggest that the interaction between Sema3A and BDNF is altered with age in vitro, and that Sema3A and Sema3F may be signaling through distinct mechanisms to alter dendritic growth at different distances from the soma. I hypothesized that these changes in the response to semaphorin treatment in cultured neurons with time in culture may be driven by a decrease in the expression of Sema3A receptors in culture. Surprisingly, Plexin-A4 and Nrp1 expression levels increased with time in culture, which is counterintuitive to what is expected as aged 30DIV neurons no longer respond to Sema3A-dependent dendritic branching in vitro. This demonstrated a need to look in vivo to better understand endogenous mechanisms and changes to dendritic morphology in the animal as it ages.
When I assessed the age-associated endogenous changes to the Nrp1 and Plexin-A4 receptor expression levels in vivo, I found an age-associated decrease in Nrp1 and Plexin-A4 expression in cortices of wildtype mice from 6 to 18 months of age, along with an associated decrease in dendritic elaboration in cortical layer V pyramidal neurons comparable to the decreased branching seen in adult PlxnA4-/- cortices. Layer V cortical pyramidal neurons from aged PlxnA4-/- mice also had decreased dendritic elaboration compared to adult and aged wildtype animals. Additionally, I examined the activity of RhoA-GTPase, a cytoskeletal regulator downstream of Plexin-A4 whose activity was previously found to inhibit dendrite outgrowth and found that RhoA activity is elevated in aged wildtype and adult PlxnA4-/- mouse cortices as compared to adult wildtype mouse cortices. Aged PlxnA4-/- mouse cortices did not have increased RhoA activity. Adult wildtype and adult PlxnA4+/- mice had similar levels of dendritic branching as well as similar levels of Plexin-A4 expression and RhoA activity. However, in aged PlxnA4+/- mice, there was no age-associated impairment in dendritic elaboration and no age-associated decrease in Plexin-A4 expression or increase in RhoA activity from 6 to 18 months of age.
Due to the changes in the dendritic arbor seen in the aged 18-month-old wildtype and adult 6-month-old PlxnA4-/- animals, in association with decreased Plexin-A4 expression levels in the aged mice, I wondered if there might be changes in cognitive function in these animals. I examined the learning ability, memory, and cognitive flexibility of these mice in the reversal learning behavioral test that requires the corticostriatal pathway, which involves the layer V cortical pyramidal neurons. I found that both adult PlxnA4-/- and aged wildtype mice have impaired learning and memory compared to adult wildtype mice, while aged PlxnA4+/- mice did not show any impairments in learning or memory, consistent with the levels of dendritic branching and molecular changes seen in those animals. Additionally, the aged PlxnA4-/- mice, the only group with decreased dendritic branching but no elevated RhoA activity, also behaved uniquely, as they did not have defects in memory compared to adult wildtype mice, as measured by winstay lever presses, but did have impairments in learning over sessions, and defects in cognitive flexibility. These results suggest that a precise level of Plexin-A4 expression is required in development for maintenance of proper cognition in aged animals, though acute deletion of Plexin-A4 in adulthood must be performed in order to confirm the role of Plexin-A4 in the aging brain.
Collectively, my findings provide novel insights into the involvement of semaphorin-plexin signaling and changes in its downstream molecular effectors, which may account for the age-associated decline of dendritic complexity and cognitive function.Ph.D.Includes bibliographical reference
Tachykinin receptors in GtoPdb v.2025.3
No full textTachykinin receptors (provisional nomenclature as recommended by NC-IUPHAR [91]) are activated by the endogenous peptides substance P (SP), neurokinin A (NKA; previously known as substance K, neurokinin α, neuromedin L), neurokinin B (NKB; previously known as neurokinin β, neuromedin K), neuropeptide K and neuropeptide γ (N-terminally extended forms of neurokinin A). The neurokinins (A and B) are mammalian members of the tachykinin family, which includes peptides of mammalian and nonmammalian origin containing the consensus sequence: Phe-x-Gly-Leu-Met. Marked species differences in in vitro pharmacology exist for all three receptors, in the context of nonpeptide ligands. Antagonists such as aprepitant and fosaprepitant were approved by FDA and EMA, in combination with other antiemetic agents, for the prevention of nausea and vomiting associated with emetogenic cancer chemotherapy
Tachykinin receptors (version 2019.4) in the IUPHAR/BPS Guide to Pharmacology Database
No full textTachykinin receptors (provisional nomenclature as recommended by NC-IUPHAR [90]) are activated by the endogenous peptides substance P (SP), neurokinin A (NKA; previously known as substance K, neurokinin α, neuromedin L), neurokinin B (NKB; previously known as neurokinin β, neuromedin K), neuropeptide K and neuropeptide γ (N-terminally extended forms of neurokinin A). The neurokinins (A and B) are mammalian members of the tachykinin family, which includes peptides of mammalian and nonmammalian origin containing the consensus sequence: Phe-x-Gly-Leu-Met. Marked species differences in in vitro pharmacology exist for all three receptors, in the context of nonpeptide ligands. Antagonists such as aprepitant and fosaprepitant were approved by FDA and EMA, in combination with other antiemetic agents, for the prevention of nausea and vomiting associated with emetogenic cancer chemotherapy
Tachykinin receptors in GtoPdb v.2023.1
No full textTachykinin receptors (provisional nomenclature as recommended by NC-IUPHAR [91]) are activated by the endogenous peptides substance P (SP), neurokinin A (NKA; previously known as substance K, neurokinin α, neuromedin L), neurokinin B (NKB; previously known as neurokinin β, neuromedin K), neuropeptide K and neuropeptide γ (N-terminally extended forms of neurokinin A). The neurokinins (A and B) are mammalian members of the tachykinin family, which includes peptides of mammalian and nonmammalian origin containing the consensus sequence: Phe-x-Gly-Leu-Met. Marked species differences in in vitro pharmacology exist for all three receptors, in the context of nonpeptide ligands. Antagonists such as aprepitant and fosaprepitant were approved by FDA and EMA, in combination with other antiemetic agents, for the prevention of nausea and vomiting associated with emetogenic cancer chemotherapy
ABCG2-augmented autophagy: an unexpected mechanism regulating cell migration
No full textThe multidrug transporter ABCG2 is best known for its ability to efflux a wide variety of compounds, but its aberrant overexpression in cancer can lead to multidrug resistance. ABCG2 plays a role in tumor cell survival by enhancing the rate of autophagy, a conserved, catabolic recycling process that breaks down damaged proteins and cellular organelles to form cellular building blocks. By augmenting autophagy, ABCG2 can enhance cell survival in the face of non-substrate stresses such as nutrient deprivation and radiation.
Conflicting reports have emerged about the impact of ABCG2 expression on cancer cell migration. Likewise, autophagy can play either a pro-metastatic or anti-metastatic role, depending on the context. Further investigation into how ABCG2-augmented autophagy may impact a highly complex and coordinated process such as cell migration is warranted.
In this study, we validated that ABCG2 overexpression enhances cancer cell migration and invasion in vitro. This is correlated to an increased expression of matrix metalloproteases and other critical cell adhesion molecules such as Focal Adhesion Kinase and Paxillin. Cell migration is attenuated when pharmacologic or genetic approaches impair either ABCG2 or autophagy. Most importantly, we observed that in the absence of functional autophagy, ABCG2 overexpression could not augment cell migration. These results show that ABCG2 expression enhances cell migration by augmenting autophagy.
ABCG2-augmented autophagy appears to regulate cell migration by altering the levels of active Rho A and Rac GTPases. Through a network of downstream signaling molecules, these proteins, and their antagonistic effect on each other, regulate cellular motility. The process of autophagy degrades the GTP-bound form of Rho A, so we hypothesized that in ABCG2 overexpressing cells, the levels of this active form of Rho A would be lower. We found that indeed, ABCG2 overexpressing cells had lower levels of active Rho A and reduced phosphorylation of myosin light chain, a downstream target of Rho A. Not expectedly, these cells also expressed higher levels of GTP-bound Rac, which is known to promote mesenchymal migration in cells. Indeed, when autophagy was inhibited, a decrease in GTP-bound Rac and an increase in GTP-bound Rho A were observed in the ABCG2 overexpressing cells. In addition to the prior observation that autophagy inhibition retards cell migration, these results show that ABCG2 overexpression enhances cell migration by tipping the balance of Rho A – Rac towards higher Rac activity and consequently increased mesenchymal migration. This study provides a novel insight into the mechanisms by which ABCG2 expression enhances cell migration which may translate to increased metastasis in vivo and in patients. Thus treatments that downregulate ABCG2 may not only help reverse multidrug resistance but may also have anti-metastatic effects.Ph.D.Includes bibliographical reference
Oncobiology and treatment of breast cancer in young women
No full text© The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2022Female breast cancer emerged as the leading cancer type in terms of incidence globally in 2020. Although mortality due to breast cancer has improved during the past three decades in many countries, this trend has reversed in women less than 40 years since the past decade. From the biological standpoint, there is consensus among experts regarding the clinically relevant definition of breast cancer in young women (BCYW), with an age cut-off of 40 years. The idea that breast cancer is an aging disease has apparently broken in the case of BCYW due to the young onset and an overall poor outcome of BCYW patients. In general, younger patients exhibit a worse prognosis than older pre- and postmenopausal patients due to the aggressive nature of cancer subtypes, a high percentage of cases with advanced stages at diagnosis, and a high risk of relapse and death in younger patients. Because of clinically and biologically unique features of BCYW, it is suspected to represent a distinct biologic entity. It is unclear why BCYW is more aggressive and has an inferior prognosis with factors that contribute to increased incidence. However, unique developmental features, adiposity and immune components of the mammary gland, hormonal interplay and crosstalk with growth factors, and a host of intrinsic and extrinsic risk factors and cellular regulatory interactions are considered to be the major contributing factors. In the present article, we discuss the status of BCYW oncobiology, therapeutic interventions and considerations, current limitations in fully understanding the basis and underlying cause(s) of BCYW, understudied areas of BCYW research, and postulated advances in the coming years for the field.info:eu-repo/semantics/publishedVersio
