Calcium Signaling

Calcium (Ca2+) signaling is a fundamental regulatory mechanism controlling essential processes in the endothelium, vascular smooth muscle cells (VSMCs), and the extracellular matrix (ECM), including maintaining the endothelial barrier, modulation of vascular tone, and vascular remodeling. Cytosolic free Ca2+ concentration is tightly regulated by a balance between Ca2+ mobilization mechanisms, including Ca2+ release from the intracellular stores in the sarcoplasmic/endoplasmic reticulum and Ca2+ entry via voltage-dependent, transient-receptor potential, and store-operated Ca2+ channels, and Ca2+ elimination pathways including Ca2+ extrusion by the plasma membrane Ca2+-ATPase and Na+/Ca2+ exchanger and Ca2+ re-uptake by the sarco(endo)plasmic reticulum Ca2+-ATPase and the mitochondria. Some cell membranes/organelles are multifunctional and have both Ca2+ mobilization and Ca2+ removal pathways. Also, the individual Ca2+ handling pathways could be integrated to function in a regenerative, capacitative, cooperative, bidirectional, or reciprocal feed-forward or feed-back manner. Disruption of these pathways causes dysregulation of the Ca2+ signaling dynamics and leads to pathological cardiovascular conditions such as hypertension, coronary artery disease, atherosclerosis, and vascular calcification. In the endothelium, dysregulated Ca2+ signaling impairs nitric oxide production, reduces vasodilatory capacity, and increases vascular permeability. In VSMCs, Ca2+-dependent phosphorylation of the myosin light chain and Ca2+ sensitization by protein kinase-C (PKC) and Rho-kinase (ROCK) increase vascular tone and could lead to increased blood pressure and hypertension. Ca2+ activation of matrix metalloproteinases causes collagen/elastin imbalance and promotes vascular remodeling. Ca2+-dependent immune cell activation, leukocyte infiltration, and cholesterol accumulation by macrophages promote foam cell formation and atherosclerotic plaque progression. Chronic increases in VSMCs Ca2+ promote phenotypic switching to mesenchymal cells and osteogenic transformation and thereby accelerate vascular calcification and plaque instability. Emerging therapeutic strategies targeting these Ca2+-dependent mechanisms, including Ca2+ channel blockers and PKC and ROCK inhibitors, hold promise for restoring Ca2+ homeostasis and mitigating vascular disease progression.

Mitochondria Sirtuins including SIRT4 erase a variety of posttranslational modifications from mitochondria proteins, leading to metabolic reprogramming that acts as a tumor suppressor, oncogenic promotor, or both. However, the factors and the underlying mechanisms that stimulate and relay such a signaling cascade are poorly understood. Here, we reveal that the voltage-gated calcium channel subunit α2δ1-mediated calcium signaling can upregulate the expression of SIRT4, which is highly expressed in α2δ1-positive pancreatic tumor-initiating cells (TICs). Furthermore, SIRT4 is functionally sufficient and indispensable to promote TIC properties of pancreatic cancer cells by directly deacetylating ENO1 at K358, leading to attenuated ENO1's RNA-binding capacity, enhanced glycolytic substrate 2-PG affinity, and subsequently robust catalytic activity with boosted glycolytic ability and increased production of lactate acid. Interestingly, both SIRT4 and deacetylated mimetic of ENO1-K358 can increase the lactylation of histones at multiple sites including H3K9 and H3K18 sites, which resulted in epigenetic reprogramming to directly activate a variety of pathways that are essential for stemness. Hence, the study links α2δ1-mediated calcium signaling to SIRT4-mediated histone lactylation epigenetic reprogramming in promoting the stem cell-like properties of pancreatic cancer, which holds significant potential for the development of novel therapeutic strategies by targeting TICs of pancreatic cancer.

Cyclic nucleotide-gated channel 5 (CNGC5), CNGC6, and CNGC9 (CNGC5/6/9 for simplicity) control Arabidopsis root hair (RH) growth by mediating the influx of external Ca2+ to establish and maintain a sharp cytosolic Ca2+ gradient at RH tips. However, the underlying mechanisms for the regulation of CNGCs remain unknown. We report here that calcium dependent protein kinase 1 (CPK1) directly activates CNGC5/6/9 to promote Arabidopsis RH growth. The loss-of-function mutants cpk1-1, cpk1-2, cngc5-1 cngc6-2 cngc9-1 (shrh1/short root hair 1), and cpk1 shrh1 show similar RH phenotypes, including shorter RHs, more RH branching, and dramatically attenuated cytosolic Ca2+ gradients at RH tips. The main CPK1-target sites are identified as Ser20, Ser27, and Ser26 for CNGC5/6/9, respectively, and the corresponding alanine substitution mutants fail to rescue RH growth in shrh1 and cpk1-1, while phospho-mimic versions restore the cytosolic Ca2+ gradient at RH apex and rescue the RH phenotypes in the same Arabidopsis mutants. Thus we discover the CPK1-CNGC modules essential for the Ca2+ signaling regulation and RH growth in Arabidopsis.

Calcium (Ca2+) signaling is integral to nearly all aspects of plant biology, including development and responses to biotic and abiotic stresses. It operates through two main layers: the generation of Ca2+ signals and their decoding by Ca2+-binding proteins, which act early in diverse signaling pathways. The system exhibits remarkable robustness and versatility, largely due to its network-like organization. While fundamental principles of Ca2+ signaling were initially established in noncrop model organisms, recent research has increasingly expanded toward major crop species and has demonstrated that natural and synthetically created variation in Ca2+ signaling components can shape agronomically important traits. In this review, we first provide a concise overview of the fundamental principles of plant Ca2+ signaling and then synthesize the current status of this research field in major crop plants. We discuss why exploiting existing natural and engineering synthetic genetic diversity in Ca2+ signaling components offers promising strategies to enhance crop stress resilience and yield stability. Subsequently, we delineate how - aided by artificial intelligence - superior alleles can be identified and/or created and incorporated into elite crop genomes. Finally, we discuss current challenges and emerging perspectives in translating Ca2+ signaling research into practical applications for crop improvement.