Biology subjects

Hildreth, M.

Publications and source records attributed to Hildreth, M..

4 recordsLinked to original sources

bioRxiv2024

ADENYLATE CYCLASE 3 MEDIATES CAROTID BODY ACTIVATION AND AUTONOMIC DYSFUNCTION IN A SLEEP APNEA MODEL

Patients with obstructive sleep apnea (OSA) experience chronic intermittent hypoxia (CIH). OSA patients and CIH-treated rodents exhibit autonomic dysfunction, characterized by overactive sympathetic nervous system and hypertension, mediated through hyperactive carotid body (CB) chemoreflex. Activation of olfactory receptor 78 (Olfr78) by hydrogen sulfide (H2S) is implicated in CB activation and autonomic responses to CIH, but the downstream signaling pathways remain unknown. Given that odorant receptor signaling is coupled to adenylyl cyclase 3 (Adcy3), we hypothesized that Adcy3-dependent cAMP contributes to CB and autonomic responses to CIH. Our findings show that CIH increases cAMP levels in the CB, a response absent in Adcy3, Cth, and Olfr78 null mice. CBs from Cth and Olfr78 mutant mice lacked persulfidation response to CIH, indicating that Adcy3 activation by CIH requires Olfr78 activation by H2S. CIH also enhanced glomus cell Ca2+ influx, an effect absent in Cnga2 and Adcy3 mutants, suggesting that CIH-induced cAMP mediates enhanced Ca2+ responses through cyclic nucleotide-gated channels. Furthermore, Adcy3 null mice did not exhibit neither CB activation nor autonomic dysfunction by CIH. These results demonstrate that Adcy3-dependent cAMP is a downstream signaling pathway to H2S/Olfr78, mediating CIH-induced CB activation and autonomic dysfunction.

physiology↗

bioRxiv2024

Reactive Oxygen species dependent increase in H3K27 acetylation by intermittent hypoxia is regulated by H3S28 phosphorylation

Histones play a crucial role in regulating gene expression through post -translational modifications (PTMS) which include acetylation, methylation and phosphorylation. We have previously identified histone 3 acetylation (H3Kac) and methylation (H3Kme) as an early epigenetic mechanism associated with intermittent hypoxia (IH), a hallmark feature of sleep apnea. The goal of the present study was to determine the molecular mechanisms underlying IH increased H3 acetylation. IH-induced H3 acetylation was blocked by an antioxidant. Conversely, reactive oxygen species (ROS) mimetics, increased H3 acetylated protein expression similar to IH, suggesting a role for ROS. Trichostatin A (TSA), an HDAC (histone deacetylase) inhibitor mimicked IH-induced H3 acetylation under normoxic conditions, while pharmacological blockade of p300/CBP (HAT, histone acetylase) with CTK7A abolished IH-induced H3 acetylation. These results suggest that interplay between HATs and HDACs regulate ROS-dependent H3 acetylation by IH. Lysine 27 (H3K27) on H3 was one of the lysines specifically acetylated by IH and this acetylation was associated with dephsophorylation of H3 at serine 28 (H3S28). Inhibition of S28 dephosphorylation by protein phosphatase inhibitors (PIC or Calyculin A), prevented H3K27 acetylation by IH. Conversely, inhibiting K27 acetylation with CTK7A, increased S28 phosphorylation in IH-exposed cells. These findings highlight the intricate balance between H3 acetylation and phosphorylation in response to IH, shedding light on epigenetic mechanism regulating gene expression. (Supported by NIH-PO1-HL90554).

cell biology↗

bioRxiv2020

Unique Proteomes Implicate Functional Specialization across Heterocysts, Akinetes, and Vegetative Cells in Anabaena cylindrica

In response to environmental changes, vegetative cells of Anabaena cylindrica can differentiate into two other cell types: a heterocyst for oxic N2-fixation, and an enlarged spore called akinete for stress survival. Akinetes normally differentiate from vegetative cells adjacent to heterocysts. Heterocysts inhibit nearby cells from differentiating into heterocysts but can induce adjacent cells to become akinetes, a rare embryogenetic induction in prokaryotes. The mechanism for a patterned differentiation in A. cylindrica has been little studied. Here, we isolated three types of cells from A. cylindrica to identify their proteomes using LC-MS/MS. A total of 1395 proteins were identified, including 664 proteins from akinetes, 751 proteins from heterocysts, and 1236 proteins from vegetative cells. There were 45 proteins (33 novel proteins) found exclusive to akinetes, 57 heterocyst-specific proteins (33 novel proteins), including nif gene products, and 485 proteins exclusively in vegetative cells. Our proteomic data suggest that akinetes, unlike the typical spores of bacteria, perform unique biochemical functions that collaborate with both heterocysts and vegetative cells. A HAVe model for collaboration among heterocysts, akinetes and vegetative cells is proposed to illustrate the metabolic network of cyanophycin and carbohydrates based on the distribution of their biosynthesis related proteins in three types of cells. Interestingly, cell division proteins, DNA replication proteins, some carboxysomal proteins including RuBisCO and proteins in photosystems I, II were found abundant in heterocysts, the non-dividing cells dedicated exclusively to oxic N2-fixation. The identification of the akinete and heterocyst proteomes enables the pursuit of genetic studies into the patterned differentiation of akinetes and heterocysts.

microbiology↗

bioRxiv2019

Unicellular Cyanobacteria Exhibit Light-Driven, Oxygen-Tolerant, Constitutive Nitrogenase Activity Under Continuous Illumination

Cyanobacteria have played a profound role in shaping the biosphere, most notably through the Great Oxygenation Event (GOE) with the advent of photosynthesis1. Cyanobacteria also contribute to global primary production through biological nitrogen fixation (BNF) using nitrogenase2,3, an oxygen-labile enzyme complex that evolutionarily predates the GOE4. Current literature reports nitrogenase activity in unicellular cyanobacteria is protected from oxygen through diurnal separation of photosynthesis and BNF5. However, historic conditions of continuous-light and warm temperature at polar latitudes during the Triassic and Cretaceous may have created a selective advantage amongst unicellular cyanobacteria for non-temporal mechanisms of maintaining nitrogenase activity in the presence of oxygen. Here we report constitutive nitrogenase activity concurrent with a net-gain of oxygen through photosynthesis in a continuous-light adapted culture of the unicellular cyanobacteria, Cyanothece sp. ATCC 51142. Nitrogenase activity in the adapted culture exhibited dependence on light and an increased resilience to artificially raised oxygen-tension compared to traditional culture. We predict cyanobacteria closely related to Cyanothece sp. ATCC 51142 also possess this physiology and found an accessory predicted proteome with functional relevance. This work provides a model of light-driven, oxygen-tolerant, constitutive nitrogenase activity and suggests this physiology may be conserved in closely related unicellular diazotrophic cyanobacteria with implications for primary production in polar ecosystems and potential biotechnological application in sustainable agriculture production.

microbiology↗