Oxidative phosphorylation and ion transport in the mitochondria of two strains of rats varying in their resistance to stress and hypoxia

Effect of high alkalinity on shrimp gills: Histopathological alternations and cell specific responses

High alkalinity stress was considered as a major risk factor for aquatic animals surviving in saline-alkaline water. However, few information exists on the effects of alkalinity stress in crustacean species. As the dominant role of gills in osmotic and ionic regulation, the present study firstly evaluated the effect of alkalinity stress in Exopalaemon carinicauda to determine changes in gill microstructure, and then explore the heterogeneity response of gill cells in alkalinity adaptation by single-cell RNA sequencing (scRNA-seq). Hemolymph osmolality and pH were increased remarkably, and gills showed pillar cells with more symmetrical arrangement and longer lateral flanges and nephrocytes with larger vacuoles in high alkalinity. ScRNA-seq results showed that alkalinity stress reduced the proportion of pillar cells and increased the proportion of nephrocytes significantly. The differentially expressed genes (DEGs) related to ion transport, especially acid-base regulation, such as V(H⁺)-ATPases and carbonic anhydrases, were down-regulated in pillar cells and up-regulated in nephrocytes. Furthermore, pseudotime analysis showed that some nephrocytes transformed to perform ion transport function in alkalinity adaption. Notedly, the positive signals of carbonic anhydrase were obviously observed in the nephrocytes after alkalinity stress. These results indicated that the alkalinity stress inhibited the ion transport function of pillar cells, but induced the active role of nephrocytes in alkalinity adaptation. Collectively, our results provided the new insight into the cellular and molecular mechanism behind the adverse effects of saline-alkaline water and the saline-alkaline adaption mechanism in crustaceans.

Highly sensitive and specific responses of shrimp gill cells to high pH stress based on single cell RNA-seq analysis

High pH is one of the main stressors affecting the shrimp survival, growth, and physiology in aquaculture ponds, but the cellular and molecular mechanism responsible for high pH stress has not been elucidated in shrimp. In this study, the shrimp acid-base disturbance and gill cell alterations were significantly observed and then single cell RNA-sequencing (scRNA-seq) was performed to study the sensitive and specific responses of gill cells to high pH stress. Three main gill cell types, including pillar cells, hemocytes and septal cells were identified. By comparative scRNA-seq analysis between control and pH group, the pillar cell was regarded as the target cell type in response to high pH stress with the down-regulation of ammonia excretion and H+ transport related genes and up-regulation of immune related genes. Notedly, high pH resulted in the emergence of a new immune cell subcluster in pillar cells, with immune activation and stress defense states. Pseudotime analysis also showed that the pillar cells could transform into the functionally inhibited ion cell subclusters and functionally activated immune cell subclusters after high pH stress. Further, the regulatory network of pillar cell population was predicted by WGCNA and two transcription factors were identified. In conclusion, these results provide key insights into the shrimp gill cell-type-specific mechanisms underlying high pH stress response at a single-cell resolution.

Mitochondrial Cyclosporine A-Independent Palmitate/Ca2+-Induced Permeability Transition Pore (PA-mPT Pore) and Its Role in Mitochondrial Function and Protection against Calcium Overload and Glutamate Toxicity

A sharp increase in the permeability of the mitochondrial inner membrane known as mitochondrial permeability transition (or mPT) occurs in mitochondria under the conditions of Ca²⁺ and ROS stress. Permeability transition can proceed through several mechanisms. The most common mechanism of mPT is based on the opening of a cyclosporine A (CSA)-sensitive protein channel in the inner membrane. In addition to the CSA-sensitive pathway, mPT can occur through the transient opening of lipid pores, emerging in the process of formation of palmitate/Ca²⁺ complexes. This pathway is independent of CSA and likely plays a protective role against Ca²⁺ and ROS toxicity. The review considers molecular mechanisms of formation and regulation of the palmitate/Ca²⁺-induced pores, which we designate as PA-mPT to distinguish it from the classical CSA-sensitive mPT. In the paper, we discuss conditions of its opening in the biological membranes, as well as its role in the physiological and pathophysiological processes. Additionally, we summarize data that indicate the involvement of PA-mPT in the protection of mitochondria against calcium overload and glutamate-induced degradation in neurons.

Current advances in the novel functions of hypoxia-inducible factor and prolyl hydroxylase in invertebrates

Oxygen is essential for aerobic life, and hypoxia has very severe consequences. Organisms need to overcome low oxygen levels to maintain biological functions during normal development and in disease states. The mechanism underlying the hypoxic response has been widely investigated in model animals such as Drosophila melanogaster and Caenorhabditis elegans. Hypoxia-inducible factor (HIF), a key gene product in the response to oxygen deprivation, is primarily regulated by prolyl hydroxylase domain enzymes (PHDs). However, recent findings have uncovered novel HIF-independent functions of PHDs. This review provides an overview of how invertebrates are able to sustain hypoxic damages, and highlights some recent discoveries in the regulation of cellular signalling by PHDs. Given that some core genes and major pathways are evolutionarily conserved, these research findings could provide insight into oxygen-sensitive signalling in mammals, and have biomedical implications for human diseases.