Detection of active cell death markers in rehydrated lichen thalli and the involvement of nitrogen monoxide (NO)

The emerging roles of nitric oxide and its associated scavengers-phytoglobins-in plant symbiotic interactions

A key feature in the establishment of symbiosis between plants and microbes is the maintenance of the balance between the production of the small redox-related molecule, nitric oxide (NO), and its cognate scavenging pathways. During the establishment of symbiosis, a transition from a normoxic to a microoxic environment often takes place, triggering the production of NO from nitrite via a reductive production pathway. Plant hemoglobins [phytoglobins (Phytogbs)] are a central tenant of NO scavenging, with NO homeostasis maintained via the Phytogb-NO cycle. While the first plant hemoglobin (leghemoglobin), associated with the symbiotic relationship between leguminous plants and bacterial Rhizobium species, was discovered in 1939, most other plant hemoglobins, identified only in the 1990s, were considered as non-symbiotic. From recent studies, it is becoming evident that the role of Phytogbs1 in the establishment and maintenance of plant-bacterial and plant-fungal symbiosis is also essential in roots. Consequently, the division of plant hemoglobins into symbiotic and non-symbiotic groups becomes less justified. While the main function of Phytogbs1 is related to the regulation of NO levels, participation of these proteins in the establishment of symbiotic relationships between plants and microorganisms represents another important dimension among the other processes in which these key redox-regulatory proteins play a central role.

Increase in NO causes osteoarthritis and chondrocyte apoptosis and chondrocyte ERK plays a protective role in the process

BACKGROUND

Nitric oxide (NO) and reactive oxygen species (ROS) play an important role in the pathology of human osteoarthritis (OA). Ankylosing spondylitis (AS) and atypical OA have similar clinical manifestations and often require differential diagnosis. The mechanism is however not totally clear yet. This study aims to investigate the effects of excessive NO-ROS in OA patients and the effects of extracellular signal-regulated kinases (ERK) pathway in NO-induced apoptosis of chondrocytes during OA progress.

METHODS AND RESULTS

Serum samples from OA or AS as pathological control patients and healthy controls were collected for NO and related chemical measurements. The rabbit articular chondrocytes were cultured in vitro, and NO was applied by Sodium Nitroprusside (SNP) in culture medium to mimic OA condition in patients. The level of SNP-evoked chondrocyte apoptosis with or without PD98059 (ERK-specific inhibitor) was evaluated by TUNEL assay, Annexin V flow cytometry and Western blotting. The activity and mRNA expression of caspase-3 in chondrocytes were measured by assay kits and RT-PCR. The levels of NO and malondialdehyde (MDA) in serum were significantly higher in OA patients, while only MDA was significantly higher in AS patients. However, the level of superoxide dismutase (SOD) was lower in both OA and AS patients. SNP induced chondrocyte apoptosis was enhanced by PD98059 with increased protein expression and functional activity of caspase-3.

CONCLUSIONS

The increase in nitric oxide occurs specifically in OA patients. ERK pathway may play a protective role on the NO-induced chondrocyte apoptosis, and inhibition of ERK pathway enhances the NO-induced apoptosis.