Glomerular Mesangial Cell pH Homeostasis Mediates Mineralocorticoid Receptor-Induced Cell Proliferation

The synergism of cytosolic acidosis and reduced NAD+/NADH ratio is responsible for lactic acidosis-induced vascular smooth muscle cell impairment in sepsis

BACKGROUND

During sepsis, serve vascular dysfunctions lead to life-threatening multiple organ failure, due to vascular smooth muscle cells (VSMC) impairments, resulting in vasoplegia, hypotension and hypoperfusion. In addition, septic patients have an altered cell metabolism that leads to lactic acidosis. Septic patients suffering from lactic acidosis have a high risk of mortality. In addition, septic survivors are at risk of secondary vascular disease. The underlying mechanisms of whether and how lactic acidosis leads to the changes in VSMCs is not well understood. The aim of this study was to comprehensively investigate the effect of lactic acidosis on VSMCs and additionally compare the effects with those induced by pure acidosis and sodium lactate.

METHODS

Primary human aortic smooth muscle cells (HAoSMCs) were treated for 48 h with lactic acidosis (LA_pH 6.8), hydrochloric acid (HCl_pH 6.8), sodium lactate (Na+-lactate_pH 7.4) and the respective controls (ctrl._pH 7.4; hyperosmolarity control: mannitol_pH 7.4) and comparatively analyzed for changes in (i) transcriptome, (ii) energy metabolism, and (iii) phenotype.

RESULTS

Both types of acidosis led to comparable and sustained intracellular acidification without affecting cell viability. RNA sequencing and detailed transcriptome analysis revealed more significant changes for lactic acidosis than for hydrochloric acidosis, with lactate being almost ineffective, suggesting qualitative and quantitative synergism of acidosis and lactate. Bioinformatic predictions in energy metabolism and phenotype were confirmed experimentally. Lactic acidosis resulted in strong inhibition of glycolysis, glutaminolysis, and altered mitochondrial respiration which reduced cellular ATP content, likely due to increased TXNIP expression and altered NAD+/NADH ratio. Hydrochloric acidosis induced significantly smaller effects without changing the NAD+/NADH ratio, with the ATP content remaining constant. These metabolic changes led to osteo-/chondrogenic/senescent transdifferentiation of VSMCs, with the effect being more pronounced in lactic acidosis than in pure acidosis.

CONCLUSIONS

Overall, lactic acidosis exerted a much stronger effect on energy metabolism than pure acidosis, whereas lactate had almost no effect, reflecting the qualitative and quantitative synergism of acidosis and lactate. As a consequence, lactic acidosis may lead to acute functional impairments of VSMC, sustained perturbations of the transcriptome and cellular dedifferentiation. Moreover, these effects may contribute to the acute and prolonged vascular pathomechanisms in septic patients.

GDF15 Interference Regulates Proliferation, Inflammation, and Autophagy of Lipopolysaccharide-induced Mesangial Cells by Inhibiting PI3K/ AKT/mTOR Signaling

BACKGROUND

Chronic glomerulonephritis (CGN) is a primary glomerular disease. As a circulating protein, growth and differentiation factor 15 (GDF15) participates in a variety of biological processes.

OBJECTIVE

We aimed to investigate the role of GDF15 in CGN.

METHODS

HBZY-1 cells were induced by lipopolysaccharide (LPS). Cell viability was detected using a cell counting kit-8 (CCK-8) assay, and a western blot was applied for the detection of GDF15 protein expression. After GDF15 silencing, cell proliferation was evaluated by CCK-8 assay and 5-ethynyl-2'-deoxyuridine (EDU) staining. Enzyme-linked immunosorbent assay (ELISA) kits were used to detect the levels of inflammatory cytokines. Autophagy was assessed by GFP-LC3B assay. Besides, the expression of NF-κB signaling-, autophagy- (LC3II/I, Beclin l and p62) and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mechanistic target of rapamycin (mTOR) signaling-related proteins were measured by western blot. Afterwards, PI3K agonist 740Y-P was used to clarify whether GDF15 affected LPS-induced HBZY-1 cells via PI3K/AKT/mTOR signaling.

RESULTS

LPS induction increased cell viability and elevated GDF15 expression in HBZY-1 cells. After GDF15 expression depletion, the increased proliferation of LPS-induced HBZY-1 cells was decreased. Additionally, GDF15 knockdown suppressed the release of inflammatory factors in LPS-induced HBZY-1 cells and activated autophagy. Moreover, the PI3K/AKT/ mTOR signal was evidenced to be activated by GDF15 deficiency. The further addition of 740Y-P reversed the impacts of GDF15 deficiency on the proliferation, inflammation, and autophagy of LPS-induced HBZY-1.

CONCLUSION

Collectively, GDF15 downregulation could protect against CGN via blocking PI3K/AKT/mTOR signaling.

The role of aldosterone in the pathogenesis of diabetic retinopathy

Aldosterone, as a mineralocorticoid of adrenal origin, has effects that are not limited to the urinary tract. As an important regulator in Vasoactive hormone pathways, aldosterone may play an effect in the pathogenesis of diabetic retinopathy (DR) through the regulation of oxidative stress, vascular regulation, and inflammatory mechanisms. This implies that mineralocorticoids, including aldosterone, have great potential and value for the diagnosis and treatment of DR. Because early studies did not focus on the intrinsic association between mineralocorticoids and DR, targeted research is still in its infancy and there are still many obstacles to its application in the clinical setting. Recent studies have improved the understanding of the effects of aldosterone on DR, and we review them with the aim of exploring possible mechanisms for the treatment and prevention of DR.