Neuronal subtype-specific transcriptomic changes in the cerebral neocortex associated with sleep pressure

Sleep is homeostatically regulated by sleep pressure, which increases during wakefulness and dissipates during sleep. Recent studies have suggested that the cerebral neocortex, a six-layered structure composed of various layer- and projection-specific neuronal subtypes, is involved in the representation of sleep pressure governed by transcriptional regulation. Here, we examined the transcriptomic changes in neuronal subtypes in the neocortex upon increased sleep pressure using single-nucleus RNA sequencing datasets and predicted the putative intracellular and intercellular molecules involved in transcriptome alterations. We revealed that sleep deprivation (SD) had the greatest effect on the transcriptome of layer 2 and 3 intratelencephalic (L2/3 IT) neurons among the neocortical glutamatergic neuronal subtypes. The expression of mutant SIK3 (SLP), which is known to increase sleep pressure, also induced profound changes in the transcriptome of L2/3 IT neurons. We identified Junb as a candidate transcription factor involved in the alteration of the L2/3 IT neuronal transcriptome by SD and SIK3 (SLP) expression. Finally, we inferred putative intercellular ligands, including BDNF, LSAMP, and PRNP, which may be involved in SD-induced alteration of the transcriptome of L2/3 IT neurons. We suggest that the transcriptome of L2/3 IT neurons is most impacted by increased sleep pressure among neocortical glutamatergic neuronal subtypes and identify putative molecules involved in such transcriptional alterations.

Knockdown of SIK3 in the CA1 Region can Reduce Seizure Susceptibility in Mice by Inhibiting Decreases in GABAAR α1 Expression

Imbalance between excitation and inhibition is an important cause of epilepsy. Salt-inducible kinase 1 (SIK1) gene mutation can cause epilepsy. In this study, we first found that the expression of SIK3 is increased after epilepsy. Furthermore, the role of SIK3 in epilepsy was explored. In cultured hippocampal neurons, we used Pterosin B, a selective SIK3 inhibitor that can inhibit epileptiform discharges induced by the convulsant drug cyclothiazide (a positive allosteric modulator of AMPA receptors, CTZ). Knockdown of SIK3 inhibited epileptiform discharges and increased the amplitude of miniature inhibitory postsynaptic currents (mIPSCs). In mice, knockdown of SIK3 reduced epilepsy susceptibility in a pentylenetetrazole (a GABAA receptor antagonist, PTZ) acute kindling experiment and increased the expression of GABAA receptor α1. In conclusion, our results suggest that blockade or knockdown of SIK3 can inhibit epileptiform discharges and that SIK3 has the potential to be a novel target for epilepsy treatment.

Downregulation of Salt-Inducible Kinase 3 Enhances CCL24 Activation in the Placental Environment with Preeclampsia

Preeclampsia (PE) remains one of the leading causes of maternal and perinatal morbidity and mortality. However, the exact pathophysiology of PE is still unclear. The recent widely accepted notion that successful pregnancy relies on maternal immunological adaptation is of utmost importance. Moreover, salt-inducible kinase 3 (SIK3) is an AMP-activated protein kinase-related kinase, and it has reported a novel regulator of energy and inflammation, and its expression related with some diseases. To explore whether SIK3 expression correlated with PE, we analyzed SIK3 gene expression and its association with PE through GEO datasets. We identified that SIK3 was significantly downregulated in PE across four datasets (p < 0.05), suggesting that SIK3 participated in the pathogenesis of PE. We initially demonstrated the significant downregulation of SIK3 in trophoblast cells of PE. SIK3 downregulation was positively correlated with the increased number of CD204(+) cells in in vivo and in vitro experiments. The increased number of CD204(+) cells could inhibit the migration and invasion of trophoblast cells. We then clarified the potential mechanism of PE with SIK3 downregulation: M2 skewing was triggered by trophoblast cells derived via the CCL24/CCR3 axis, leading to an increase in CD204(+) cells, a decrease in phagocytosis, and the production of IL-10 at the maternal-fetal interface of the placenta with PE. IL-10 further contributed to a reduction in the migration and invasion of trophoblast cells. It also established a feedback loop wherein trophoblast cells increased CCL24 production to maintain M2 dominance in the placental environments of PE.

Sleep need, the key regulator of sleep homeostasis, is indicated and controlled by phosphorylation of threonine 221 in salt-inducible kinase 3

Sleep need drives sleep and plays a key role in homeostatic regulation of sleep. So far sleep need can only be inferred by animal behaviors and indicated by electroencephalography (EEG). Here we report that phosphorylation of threonine (T) 221 of the salt-inducible kinase 3 (SIK3) increased the catalytic activity and stability of SIK3. T221 phosphorylation in the mouse brain indicates sleep need: more sleep resulting in less phosphorylation and less sleep more phosphorylation during daily sleep/wake cycle and after sleep deprivation (SD). Sleep need was reduced in SIK3 loss of function (LOF) mutants and by T221 mutation to alanine (T221A). Rebound after SD was also decreased in SIK3 LOF and T221A mutant mice. By contrast, SIK1 and SIK2 do not satisfy criteria to be both an indicator and a controller of sleep need. Our results reveal SIK3-T221 phosphorylation as a chemical modification which indicates and controls sleep need.

Salt-inducible kinase inhibition promotes the adipocyte thermogenic program and adipose tissue browning

OBJECTIVE

Norepinephrine stimulates the adipose tissue thermogenic program through a β-adrenergic receptor (βAR)-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling cascade. We discovered that a noncanonical activation of the mechanistic target of rapamycin complex 1 (mTORC1) by PKA is required for the βAR-stimulation of adipose tissue browning. However, the downstream events triggered by PKA-phosphorylated mTORC1 activation that drive this thermogenic response are not well understood.

METHODS

We used a proteomic approach of Stable Isotope Labeling by/with Amino acids in Cell culture (SILAC) to characterize the global protein phosphorylation profile in brown adipocytes treated with the βAR agonist. We identified salt-inducible kinase 3 (SIK3) as a candidate mTORC1 substrate and further tested the effect of SIK3 deficiency or SIK inhibition on the thermogenic gene expression program in brown adipocytes and in mouse adipose tissue.

RESULTS

SIK3 interacts with RAPTOR, the defining component of the mTORC1 complex, and is phosphorylated at Ser884 in a rapamycin-sensitive manner. Pharmacological SIK inhibition by a pan-SIK inhibitor (HG-9-91-01) in brown adipocytes increases basal Ucp1 gene expression and restores its expression upon blockade of either mTORC1 or PKA. Short-hairpin RNA (shRNA) knockdown of Sik3 augments, while overexpression of SIK3 suppresses, Ucp1 gene expression in brown adipocytes. The regulatory PKA phosphorylation domain of SIK3 is essential for its inhibition. CRISPR-mediated Sik3 deletion in brown adipocytes increases type IIa histone deacetylase (HDAC) activity and enhances the expression of genes involved in thermogenesis such as Ucp1, Pgc1α, and mitochondrial OXPHOS complex protein. We further show that HDAC4 interacts with PGC1α after βAR stimulation and reduces lysine acetylation in PGC1α. Finally, a SIK inhibitor well-tolerated in vivo (YKL-05-099) can stimulate the expression of thermogenesis-related genes and browning of mouse subcutaneous adipose tissue.

CONCLUSIONS

Taken together, our data reveal that SIK3, with the possible contribution of other SIKs, functions as a phosphorylation switch for β-adrenergic activation to drive the adipose tissue thermogenic program and indicates that more work to understand the role of the SIKs is warranted. Our findings also suggest that maneuvers targeting SIKs could be beneficial for obesity and related cardiometabolic disease.

SIK3-HDAC4 in the suprachiasmatic nucleus regulates the timing of arousal at the dark onset and circadian period in mice

Mammals exhibit circadian cycles of sleep and wakefulness under the control of the suprachiasmatic nucleus (SCN), such as the strong arousal phase-locked to the beginning of the dark phase in laboratory mice. Here, we demonstrate that salt-inducible kinase 3 (SIK3) deficiency in gamma-aminobutyric acid (GABA)-ergic neurons or neuromedin S (NMS)-producing neurons delayed the arousal peak phase and lengthened the behavioral circadian cycle under both 12-h light:12-h dark condition (LD) and constant dark condition (DD) without changing daily sleep amounts. In contrast, the induction of a gain-of-function mutant allele of Sik3 in GABAergic neurons exhibited advanced activity onset and a shorter circadian period. Loss of SIK3 in arginine vasopressin (AVP)-producing neurons lengthened the circadian cycle, but the arousal peak phase was similar to that in control mice. Heterozygous deficiency of histone deacetylase (HDAC) 4, a SIK3 substrate, shortened the circadian cycle, whereas mice with HDAC4 S245A, which is resistant to phosphorylation by SIK3, delayed the arousal peak phase. Phase-delayed core clock gene expressions were detected in the liver of mice lacking SIK3 in GABAergic neurons. These results suggest that the SIK3-HDAC4 pathway regulates the circadian period length and the timing of arousal through NMS-positive neurons in the SCN.

Salt-inducible kinase 2 regulates fibrosis during bleomycin-induced lung injury

Idiopathic pulmonary fibrosis is a progressive and normally fatal disease with limited treatment options. The tyrosine kinase inhibitor nintedanib has recently been approved for the treatment of idiopathic pulmonary fibrosis, and its effectiveness has been linked to its ability to inhibit a number of receptor tyrosine kinases including the platelet-derived growth factor, vascular endothelial growth factor, and fibroblast growth factor receptors. We show here that nintedanib also inhibits salt-inducible kinase 2 (SIK2), with a similar IC50 to its reported tyrosine kinase targets. Nintedanib also inhibited the related kinases SIK1 and SIK3, although with 12-fold and 72-fold higher IC50s, respectively. To investigate if the inhibition of SIK2 may contribute to the effectiveness of nintedanib in treating lung fibrosis, mice with kinase-inactive knockin mutations were tested using a model of bleomycin-induced lung fibrosis. We found that loss of SIK2 activity protects against bleomycin-induced fibrosis, as judged by collagen deposition and histological scoring. Loss of both SIK1 and SIK2 activity had a similar effect to loss of SIK2 activity. Total SIK3 knockout mice have a developmental phenotype making them unsuitable for analysis in this model; however, we determined that conditional knockout of SIK3 in the immune system did not affect bleomycin-induced lung fibrosis. Together, these results suggest that SIK2 is a potential drug target for the treatment of lung fibrosis.

The role of microglial/macrophagic salt-inducible kinase 3 on normal and excessive phagocytosis after transient focal cerebral ischemia

Previous studies suggested that anti-inflammatory microglia/macrophages (Mi/MΦ) play a role in “normal phagocytosis,” which promoted the rapid clearance of necrotic substances and apoptotic cells. More recently, a few studies have found that Mi/MΦ also play a role in “pathological phagocytosis” in the form of excessive or reduced phagocytosis, thereby worsening damage induced by CNS diseases. However, the underlying mechanisms and the Mi/MΦ subtypes related to this pathological phagocytosis are still unknown. Salt-inducible kinase 3 (SIK3), a member of the 5’ adenosine monophosphate-activated protein kinase (AMPK) family, has been shown to regulate inflammation in several peripheral diseases. Whether SIK3 also regulates the inflammatory response in CNS diseases is currently unknown. Therefore, in this study, we created a transgenic tamoxifen-induced Mi/MΦ-specific SIK3 conditional knockout (SIK3-cKO) mouse to examine SIK3’s role in phagocytotic function induced by transient focal cerebral ischemia (tFCI). By single-cell RNA-seq, we found the pro-inflammatory Mi/MΦ phenotype performed an excessive phagocytotic function, but the anti-inflammatory Mi/MΦ phenotype performed a normal phagocytotic function. We found that SIK3-cKO caused Mi/MΦ heterogenization from the transitional phenotype to the anti-inflammatory phenotype after tFCI. This phenotypic shift corresponded with enhanced phagocytosis of both apoptotic and live neurons. Interestingly, SIK3-cKO enhanced normal phagocytosis of myelin debris but attenuating excessive phagocytosis of non-damaged myelin sheath, thereby protecting white matter integrity after tFCI. CD16, a pro-inflammation marker, was decreased significantly by SIK3-cKO and correlated with “excessive phagocytosis.” SIK3-cKO promoted long-term recovery of white matter function and neurological function as assessed with electrophysiological compound action potential (CAPs) and behavioral analysis. This study is the first to show a role of SIK3 in Mi/MΦ phagocytosis in CNS diseases, and reveals that promoting Mi/MΦ anti-inflammatory heterogenization inhibits “excessive phagocytosis” of live cells and facilitates “normal phagocytosis” of apoptotic cells. Therefore, inhibition of SIK3 in Mi/MΦ may be a potential therapeutic target in stroke and other CNS diseases with accompanying white matter destruction.

A whole-exome case-control association study to characterize the contribution of rare coding variation to pancreatic cancer risk

Pancreatic cancer is a deadly disease that accounts for approximately 5% of cancer deaths worldwide, with a dismal 5-year survival rate of 10%. Known genetic risk factors explain only a modest proportion of the heritable risk of pancreatic cancer. We conducted a whole-exome case-control sequencing study in 1,591 pancreatic cancer cases and 2,134 cancer-free controls of European ancestry. In our gene-based analysis, ATM ranked first, with a genome-wide significant p value of 1 × 10-8. The odds ratio for protein-truncating variants in ATM was 24, which is substantially higher than prior estimates, although ours includes a broad 95% confidence interval (4.0-1000). SIK3 was the second highest ranking gene (p = 3.84 × 10-6, false discovery rate or FDR = 0.032). We observed nominally significant association signals in several genes of a priori interest, including BRCA2 (p = 4.3 × 10-4), STK11 (p = 0.003), PALB2 (p = 0.019), and TP53 (p = 0.037), and reported risk estimates for known pathogenic variants and variants of uncertain significance (VUS) in these genes. The rare variants in established susceptibility genes explain approximately 24% of log familial relative risk, which is comparable to the contribution from established common susceptibility variants (17%). In conclusion, this study provides new insights into the genetic susceptibility of pancreatic cancer, refining rare variant risk estimates in known pancreatic cancer susceptibility genes and identifying SIK3 as a novel candidate susceptibility gene. This study highlights the prominent importance of ATM truncating variants and the underappreciated role of VUS in pancreatic cancer etiology.

Induction of Mutant Sik3Sleepy Allele in Neurons in Late Infancy Increases Sleep Need

Sleep is regulated in a homeostatic manner. Sleep deprivation increases sleep need, which is compensated mainly by increased EEG δ power during non-rapid eye movement sleep (NREMS) and, to a lesser extent, by increased sleep amount. Although genetic factors determine the constitutive level of sleep need and sleep amount in mice and humans, the molecular entity behind sleep need remains unknown. Recently, we found that a gain-of-function Sleepy (Slp) mutation in the salt-inducible kinase 3 (Sik3) gene, which produces the mutant SIK3(SLP) protein, leads to an increase in NREMS EEG δ power and sleep amount. Since Sik3^Slp mice express SIK3(SLP) in various types of cells in the brain as well as multiple peripheral tissues from the embryonic stage, the cell type and developmental stage responsible for the sleep phenotype in Sik3^Slp mice remain to be elucidated. Here, we generated two mouse lines, synapsin1^CreERT2 and Sik3^ex13flox mice, which enable inducible Cre-mediated, conditional expression of SIK3(SLP) in neurons on tamoxifen administration. Administration of tamoxifen to synapsin1^CreERT2 mice during late infancy resulted in higher recombination efficiency than administration during adolescence. SIK3(SLP) expression after late infancy increased NREMS and NREMS δ power in male synapsin1^CreERT2; Sik3 ^ex13flox/+ mice. The expression of SIK3(SLP) after adolescence led to a higher NREMS δ power without a significant change in NREMS amounts. Thus, neuron-specific expression of SIK3(SLP) after late infancy is sufficient to increase sleep.SIGNIFICANCE STATEMENT The propensity to accumulate sleep need during wakefulness and to dissipate it during sleep underlies the homeostatic regulation of sleep. However, little is known about the developmental stage and cell types involved in determining the homeostatic regulation of sleep. Here, we show that Sik3^Slp allele induction in mature neurons in late infancy is sufficient to increase non-rapid eye movement sleep amount and non-rapid eye movement sleep δ power. SIK3 signaling in neurons constitutes an intracellular mechanism to increase sleep.

Distinctive role of SIK1 and SIK3 isoforms in aerobic glycolysis and cell growth of breast cancer through the regulation of p53 and mTOR signaling pathways

The Salt-inducible kinase (SIKs) belongs to an AMPK-related family kinase, an isoform of the SIK family, SIK1 gets frequently downregulated in various types of cancer contribute to tumorigenesis. However, its precise role in breast cancer and the relevant molecular mechanism remains unclear. Herein, analysis of the clinical data reveals that SIK1 expression was significantly downregulated in breast cancer tissues, and closely associated with poor survival rate in breast cancer. SIK1 is functionally stimulating oxidative phosphorylation, which in turn inhibits aerobic glycolysis and cell proliferation in breast cancer cells. Mechanistically, SIK1 directly interacted with p53 and positively regulates its transcriptional activity, thereby facilitates oxidative phosphorylation in breast cancer cells. The knockdown of SIK1 downregulates p53 transcriptional activity, leading to stimulation of aerobic glycolysis and cell proliferation. Moreover, high expression of SIK3 stimulates mTOR-mediated aerobic glycolysis and cell proliferation of breast cancer cells. These findings suggest that SIK isoforms plays distinct role in aerobic glycolysis and cell growth of breast cancer, attenuated SIK1/p53 signaling suppresses oxidative phosphorylation and growth inhibitory effect in breast cancer cells, while enhanced SIK3/mTOR signaling potentiates aerobic glycolysis mediated cell growth in breast cancer cells.

Berberine and Emodin abrogates breast cancer growth and facilitates apoptosis through inactivation of SIK3-induced mTOR and Akt signaling pathway

Salt-inducible kinases 3 (SIK3) belong to the AMPK-related family of kinases, which have been implicated in the regulation of cell metabolism, cell polarity remodelling, and epithelial-mesenchymal transition. Elevated SIK3 expressions in breast cancer cells are shown to contribute to tumorigenesis; however, the underlying mechanism remains to be elucidated. In this study, we demonstrate that SIK3 expression is upregulated and concurrently high expression of SIK3 is associated with poor survival in breast cancer. Specifically, SIK3 knockdown revealed that SIK3 is required for the mTOR/Akt signaling pathway and proliferation of breast cancer cells. Furthermore, our findings showed that Emodin (EMO) combined with Berberine (BBR) significantly inhibited SIK3 activity, leading to reduced cell growth, increased cell cycle arrest and apoptosis in breast cancer cells, but not in non-malignant breast epithelial cell line. Mechanistic studies further reveal that EMO and BBR in combined treatment inhibited SIK3-potentiated mTOR-mediated aerobic glycolysis and cell growth in breast cancer cells. Moreover, combination treatments attenuate Akt signaling, thereby inducing G0/G1 phase cell cycle arrest and apoptosis of breast cancer cells in a SIK3-dependent manner. CRISPR/Cas9 or siRNA-mediated SIK3 knockout/knockdown showed an opposite trend in both the luminal and basal-like breast cancer. Collectively, our findings reveal that combination of EMO and BBR attenuates SIK3-driven tumor growth in breast cancer, and thus, EMO and BBR might be a novel SIK3 inhibitor explored into the prevention of breast cancer.

M2 Macrophagy-derived exosomal miRNA-5106 induces bone mesenchymal stem cells towards osteoblastic fate by targeting salt-inducible kinase 2 and 3

Background

Osteoblast differentiation is a vital process for fracture healing, and exosomes are nanosized membrane vesicles that can deliver therapeutic drugs easily and safely. Macrophages participate in the regulation of various biological processes in vivo, and macrophage-derived exosomes (MD-Exos) have recently been a topic of increasing research interest. However, few study has explored the link between MD-Exos and osteoblast differentiation. Herein, we sought to identify miRNAs differentially expressed between M1 and M2 macrophage-derived exosomes, and to evaluate their roles in the context of osteoblast differentiation.

Results

We found that microRNA-5106 (miR-5106) was significantly overexpressed in M2 macrophage-derived exosomes (M2D-Exos), while its expression was decreased in M1 macrophage-derived exosomes (M1D-Exos), and we found that this exosomal miRNA can induce bone mesenchymal stem cell (BMSC) osteogenic differentiation via directly targeting the Salt-inducible kinase 2 and 3 (SIK2 and SIK3) genes. In addition, the local injection of both a miR-5106 agonist or M2D-Exos to fracture sites was sufficient to accelerate healing in vivo.

Conclusions

Our study demonstrates that miR-5106 is highly enriched in M2D-Exos, and that it can be transferred to BMSCs wherein it targets SIK2 and SIK3 genes to promote osteoblast differentiation.

Salt-Inducible Kinase 3 Haplotypes Associated with Noise-Induced Hearing Loss in Chinese Workers

INTRODUCTION

Noise-induced hearing loss (NIHL) is a common occupational disease that represents an irreversible hearing damage to the auditory system. It has been identified as a complicated disease involving both environmental and genetic factors. More efforts need to be made to explore the genes associated with susceptibility to NIHL. The main aim of this research is to detect the associations between SIK3 polymorphisms and NIHL susceptibility in Han people in China.

METHODS

A case-control study was performed in 586 cases and 639 controls in a textile factory matched for sex, age, smoking, drinking, work time with noise, and intensity of noise exposure. Three single nucleotide polymorphisms (SNPs) (rs493134, rs6589574, and rs7121898) of SIK3 were genotyped in the participants. Then, the main influences of the SNPs on and their interactions with NIHL were assessed.

RESULTS

Under the allelic model, distributions of rs493134 T, rs6589574 G, and rs7121898 A in the NIHL group are statistically different from those of the normal group (p = 0.001, p < 0.001, and p = 0.019, respectively). The following haplotype analysis shows that TAA (rs493134-rs6589574-rs7121898) may have a protective effect, while TGA (rs493134-rs6589574-rs7121898) (OR = 1.49, 95% CI = 1.25-1.79) may be a risk factor for NIHL. Multifactor dimensionality reduction analysis shows that the interaction of the 3 selected SNPs is associated with NIHL susceptibility (OR = 1.88, 95% CI = 1.50-2.36).

CONCLUSION

The results suggest that 3 SNPs (rs493134, rs6589574, and rs7121898) of SIK3 may be an important part of NIHL susceptibility and can be applied in the prevention, early diagnosis, and treatment of NIHL in noise-exposed Chinese workers.

Downregulated Salt-inducible Kinase 3 Expression Promotes Chemoresistance in Serous Ovarian Cancer via the ATP-binding Cassette Protein ABCG2

Background: Epithelial ovarian cancer (EOC) has a high tumor-associated mortality rate among gynecological cancers. Although CA125 is a well-studied biomarker for ovarian cancer, it is also elevated under numerous conditions, resulting in decreased specificity. Recently, we identified a novel tumor-associated antigen, salt-inducible kinase 3 (SIK3), during tumorigenesis in ovarian cancer. However, the association between SIK3 expression and patient outcomes in ovarian cancer remains unclear.

Materials and Methods: We collected EOC samples from 204 patients and examined tumor SIK3 expression by immunohistochemistry (IHC) and CA125 expression in tumors and serum. The expression levels of SIK3 and CA125 were correlated with patient survival. SIK3 expression was silenced with SIK3-specific shRNAs to investigate the possible mechanisms related to chemoresistance in serous-type ovarian cancer cell lines OVCAR4 and SKOV3.

Results: In advanced-stage serous ovarian cancer, patients with low SIK3 expression have poorer overall survival (OS) and progression-free survival (PFS) than patients with high SIK3 expression. Ovarian cancer cells with SIK3 knockdown display increased chemoresistance to Taxol plus cisplatin treatment, which is associated with the upregulation of the ABCG2 transporter. In addition, in serous ovarian cancer, SIK3 expression is inversely correlated to ABCG2 expression, and patients with low SIK3 and high ABCG2 expression have worse prognosis than patients with high SIK3 and low ABCG2 expression.

Conclusion: Our results demonstrated that serous EOC patients with low SIK3 expression have poor prognosis, which is associated with chemoresistance mediated by ABCG2 upregulation. SIK3 and ABCG2 expression levels may be potential prognostic markers to predict the outcome in serous EOC patients.

LKB1, Salt-Inducible Kinases, and MEF2C Are Linked Dependencies in Acute Myeloid Leukemia

The lineage-specific transcription factor (TF) MEF2C is often deregulated in leukemia. However, strategies to target this TF have yet to be identified. Here, we used a domain-focused CRISPR screen to reveal an essential role for LKB1 and its Salt-Inducible Kinase effectors (SIK3, in a partially redundant manner with SIK2) to maintain MEF2C function in acute myeloid leukemia (AML). A key phosphorylation substrate of SIK3 in this context is HDAC4, a repressive cofactor of MEF2C. Consequently, targeting of LKB1 or SIK3 diminishes histone acetylation at MEF2C-bound enhancers and deprives leukemia cells of the output of this essential TF. We also found that MEF2C-dependent leukemias are sensitive to on-target chemical inhibition of SIK activity. This study reveals a chemical strategy to block MEF2C function in AML, highlighting how an oncogenic TF can be disabled by targeting of upstream kinases.

Salt-inducible kinase 3 regulates the mammalian circadian clock by destabilizing PER2 protein

Salt-inducible kinase 3 (SIK3) plays a crucial role in various aspects of metabolism. In the course of investigating metabolic defects in Sik3-deficient mice (Sik3^-/-), we observed that circadian rhythmicity of the metabolisms was phase-delayed. Sik3^-/- mice also exhibited other circadian abnormalities, including lengthening of the period, impaired entrainment to the light-dark cycle, phase variation in locomotor activities, and aberrant physiological rhythms. Ex vivo suprachiasmatic nucleus slices from Sik3^-/- mice exhibited destabilized and desynchronized molecular rhythms among individual neurons. In cultured cells, Sik3-knockdown resulted in abnormal bioluminescence rhythms. Expression levels of PER2, a clock protein, were elevated in Sik3-knockdown cells but down-regulated in Sik3-overexpressing cells, which could be attributed to a phosphorylation-dependent decrease in PER2 protein stability. This was further confirmed by PER2 accumulation in the Sik3^-/- fibroblasts and liver. Collectively, SIK3 plays key roles in circadian rhythms by facilitating phosphorylation-dependent PER2 destabilization, either directly or indirectly.

SIK3-HDAC4 signaling regulates Drosophila circadian male sex drive rhythm via modulating the DN1 clock neurons

The physiology and behavior of many organisms are subject to daily cycles. In Drosophila melanogaster the daily locomotion patterns of single flies are characterized by bursts of activity at dawn and dusk. Two distinct clusters of clock neurons-morning oscillators (M cells) and evening oscillators (E cells)-are largely responsible for these activity bursts. In contrast, male-female pairs of flies follow a distinct pattern, most notably characterized by an activity trough at dusk followed by a high level of male courtship during the night. This male sex drive rhythm (MSDR) is mediated by the M cells along with DN1 neurons, a cluster of clock neurons located in the dorsal posterior region of the brain. Here we report that males lacking Salt-inducible kinase 3 (SIK3) expression in M cells exhibit a short period of MSDR but a long period of single-fly locomotor rhythm (SLR). Moreover, lack of Sik3 in M cells decreases the amplitude of PERIOD (PER) cycling in DN1 neurons, suggesting that SIK3 non-cell-autonomously regulates DN1 neurons' molecular clock. We also show that Sik3 reduction interferes with circadian nucleocytoplasmic shuttling of Histone deacetylase 4 (HDAC4), a SIK3 phosphorylation target, in clock neurons and that constitutive HDAC4 localization in the nucleus shortens the period of MSDR. Taking these findings together, we conclude that SIK3-HDAC4 signaling in M cells regulates MSDR by regulating the molecular oscillation in DN1 neurons.

Genetic variants in SERPINA4 and SERPINA5, but not BCL2 and SIK3 are associated with acute kidney injury in critically ill patients with septic shock

Background

Acute kidney injury (AKI) is a multifactorial syndrome, but knowledge about its pathophysiology and possible genetic background is limited. Recently the first hypothesis-free genetic association studies have been published to explore individual susceptibility to AKI. We aimed to replicate the previously identified associations between five candidate single nucleotide polymorphisms (SNP) in apoptosis-related genes BCL2, SERPINA4, SERPINA5, and SIK3 and the development of AKI, using a prospective cohort of critically ill patients with sepsis/septic shock, in Finland.

Methods

This is a prospective, observational multicenter study. Of 2567 patients without chronic kidney disease and with genetic samples included in the Finnish Acute Kidney Injury (FINNAKI) study, 837 patients had sepsis and 627 patients had septic shock. AKI was defined according to the Kidney Disease: Improving Global Outcomes (KDIGO) criteria, considering stages 2 and 3 affected (severe AKI), stage 0 unaffected, and stage 1 indecisive. Genotyping was done using iPLEX^TM Assay (Agena Bioscience). The genotyped SNPs were rs8094315 and rs12457893 in the intron of the BCL2 gene, rs2093266 in the SERPINA4 gene, rs1955656 in the SERPINA5 gene and rs625145 in the SIK3 gene. Association analyses were performed using logistic regression with PLINK software.

Results

We found no significant associations between the SNPs and severe AKI in patients with sepsis/septic shock, even after adjustment for confounders. Among patients with septic shock (252 with severe AKI and 226 without AKI (149 with KDIGO stage 1 excluded)), the SNPs rs2093266 and rs1955656 were significantly (odds ratio 0.63, p = 0.04276) associated with stage 2–3 AKI after adjusting for clinical and demographic variables.

Conclusions

The SNPs rs2093266 in the SERPINA4 and rs1955656 in the SERPINA5 were associated with the development of severe AKI (KDIGO stage 2–3) in critically ill patients with septic shock. For the other SNPs, we did not confirm the previously reported associations.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1631-3) contains supplementary material, which is available to authorized users.

Salt-inducible kinase 2 and -3 are downregulated in adipose tissue from obese or insulin-resistant individuals: implications for insulin signalling and glucose uptake in human adipocytes

AIMS/HYPOTHESIS

Salt-inducible kinases (SIKs) are related to the metabolic regulator AMP-activated protein kinase (AMPK). SIK2 is abundant in adipose tissue. The aims of this study were to investigate the expression of SIKs in relation to human obesity and insulin resistance, and to evaluate whether changes in the expression of SIKs might play a causal role in the development of disturbed glucose uptake in human adipocytes.

METHODS

SIK mRNA and protein was determined in human adipose tissue or adipocytes, and correlated to clinical variables. SIK2 and SIK3 expression and phosphorylation were analysed in adipocytes treated with TNF-α. Glucose uptake, GLUT protein levels and localisation, phosphorylation of protein kinase B (PKB/Akt) and the SIK substrate histone deacetylase 4 (HDAC4) were analysed after the SIKs had been silenced using small interfering RNA (siRNA) or inhibited using a pan-SIK-inhibitor (HG-9-91-01).

RESULTS

We demonstrate that SIK2 and SIK3 mRNA are downregulated in adipose tissue from obese individuals and that the expression is regulated by weight change. SIK2 is also negatively associated with in vivo insulin resistance (HOMA-IR), independently of BMI and age. Moreover, SIK2 protein levels and specific kinase activity display a negative correlation to BMI in human adipocytes. Furthermore, SIK2 and SIK3 are downregulated by TNF-α in adipocytes. Silencing or inhibiting SIK1-3 in adipocytes results in reduced phosphorylation of HDAC4 and PKB/Akt, less GLUT4 at the plasma membrane, and lower basal and insulin-stimulated glucose uptake in adipocytes.

CONCLUSION/INTERPRETATION

This is the first study to describe the expression and function of SIKs in human adipocytes. Our data suggest that SIKs might be protective in the development of obesity-induced insulin resistance, with implications for future treatment strategies.

Salt-Inducible Kinase 3 Provides Sugar Tolerance by Regulating NADPH/NADP+ Redox Balance

Nutrient-sensing pathways respond to changes in the levels of macronutrients, such as sugars, lipids, or amino acids, and regulate metabolic pathways to maintain organismal homeostasis [1, 2]. Consequently, nutrient sensing provides animals with the metabolic flexibility necessary for enduring temporal fluctuations in nutrient intake. Recent studies have shown that an animal's ability to survive on a high-sugar diet is determined by sugar-responsive gene regulation [3-8]. It remains to be elucidated whether other levels of metabolic control, such as post-translational regulation of metabolic enzymes, also contribute to organismal sugar tolerance. Furthermore, the sugar-regulated metabolic pathways contributing to sugar tolerance remain insufficiently characterized. Here, we identify Salt-inducible kinase 3 (SIK3), a member of the AMP-activated protein kinase (AMPK)-related kinase family, as a key determinant of Drosophila sugar tolerance. SIK3 allows sugar-feeding animals to increase the reductive capacity of nicotinamide adenine dinucleotide phosphate (NADPH/NADP⁺). NADPH mediates the reduction of the intracellular antioxidant glutathione, which is essential for survival on a high-sugar diet. SIK3 controls NADP⁺ reduction by phosphorylating and activating Glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway. SIK3 gene expression is regulated by the sugar-regulated transcription factor complex Mondo-Mlx, which was previously identified as a key determinant of sugar tolerance. SIK3 converges with Mondo-Mlx in sugar-induced activation of G6PD, and simultaneous inhibition of SIK3 and Mondo-Mlx leads to strong synergistic lethality on a sugar-containing diet. In conclusion, SIK3 cooperates with Mondo-Mlx to maintain organismal sugar tolerance through the regulation of NADPH/NADP⁺ redox balance.