SGLT2 inhibitors act as metabolic transducers to restore healthy nutrient deprivation and surplus signaling in the kidney

In the healthy adult kidney, cellular homeostasis is maintained by the balance between nutrient surplus and nutrient deprivation signaling.1Packer M. Fetal reprogramming of nutrient surplus signaling, O-GlcNAcylation, and the evolution of CKD.J Am Soc Nephrol. 2023; 34: 1480-1491Crossref Scopus (3) Google Scholar The primary nutrient deprivation signals are sirtuin 1 (SIRT1) and adenosine monophosphate protein kinase (AMPK), which are activated by low intracellular levels of glucose and adenosine triphosphate (ATP) and by the oxidation-reduction state, and function to reduce oxidative stress and proinflammatory signaling, thus promoting cellular survival. The primary nutrient surplus signals are mammalian target of rapamycin (mTOR) and hypoxia-inducible factor-1α (HIF-1α), which are activated by high intracellular levels of glucose to enhance flux through glucose-driven anabolic pathways and to promote maladaptive tubular hypertrophy, oxidative stress, inflammation, fibrosis, and apoptosis. Typically, the balancing of nutrient deprivation and surplus pathways maintains kidney health, with nutrient deprivation signals being dominant, thereby ensuring a reduced level of cellular stress that promotes cellular survival, particularly in the proximal renal tubule and glomerular podocytes and mesangial cells. Chronic kidney disease is characterized by an increase in cellular glucose uptake, which triggers upregulation of nutrient surplus signaling (mTOR and HIF-1α) and downregulation of nutrient deprivation signals (SIRT1 and AMPK).1Packer M. Fetal reprogramming of nutrient surplus signaling, O-GlcNAcylation, and the evolution of CKD.J Am Soc Nephrol. 2023; 34: 1480-1491Crossref Scopus (3) Google Scholar,2Packer M. Role of impaired nutrient and oxygen deprivation signaling and deficient autophagic flux in diabetic CKD development: implications for understanding the effects of sodium-glucose cotransporter 2-inhibitors.J Am Soc Nephrol. 2020; 31: 907-919Crossref PubMed Scopus (80) Google Scholar The convergent result is to enhance oxidative stress in the proximal tubule and the glomerulus, while promoting renal inflammation, apoptosis, and fibrosis. Activation of mTOR/HIF-1α and increased flux through the pentose phosphate pathway directs glucose away from ATP production and toward anabolic pathways, thus driving proximal tubular cells into the cell cycle. However, under high-workload normoxic conditions, cells driven toward growth exhibit maladaptive dedifferentiation rather than tubular renewal, leading to renal structural and functional disarray.1Packer M. Fetal reprogramming of nutrient surplus signaling, O-GlcNAcylation, and the evolution of CKD.J Am Soc Nephrol. 2023; 34: 1480-1491Crossref Scopus (3) Google Scholar The activation of mTOR/HIF-1α is particularly notable in the proximal renal tubule, where it drives the development of albuminuria and fibrosis in the renal cortex, and underlies the progression of chronic kidney disease.3Kogot-Levin A. Hinden L. Riahi Y. et al.Proximal tubule mTORC1 is a central player in the pathophysiology of diabetic nephropathy and its correction by SGLT2 inhibitors.Cell Rep. 2020; 32107954Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar Furthermore, the simultaneous suppression of SIRT1/AMPK signaling in the proximal tubule abrogates the ability of these nutrient deprivation signals to promote mitochondrial biogenesis and mitophagy, the housekeeping pathway that allows cells to dispose of dysfunctional mitochondria and, thereby, maintain ATP production.1Packer M. Fetal reprogramming of nutrient surplus signaling, O-GlcNAcylation, and the evolution of CKD.J Am Soc Nephrol. 2023; 34: 1480-1491Crossref Scopus (3) Google Scholar,2Packer M. Role of impaired nutrient and oxygen deprivation signaling and deficient autophagic flux in diabetic CKD development: implications for understanding the effects of sodium-glucose cotransporter 2-inhibitors.J Am Soc Nephrol. 2020; 31: 907-919Crossref PubMed Scopus (80) Google Scholar This sequence of events explains the exceptional degree of structural and functional mitochondrial abnormalities seen in the proximal tubule and glomerular podocytes in chronic kidney disease.4Packer M. Critical reanalysis of the mechanisms underlying the cardiorenal benefits of SGLT2 inhibitors and reaffirmation of the nutrient deprivation signaling/autophagy hypothesis.Circulation. 2022; 146: 1383-1405Crossref PubMed Scopus (136) Google Scholar Sodium-glucose cotransporter 2 (SGLT2) inhibitors act to block the transport of glucose into the proximal tubule, and they also trigger a system-wide state of fasting mimicry, which is characterized by enhanced gluconeogenesis and ketogenesis. Under healthy conditions, the proximal tubule is the second most important source of gluconeogenesis.2Packer M. Role of impaired nutrient and oxygen deprivation signaling and deficient autophagic flux in diabetic CKD development: implications for understanding the effects of sodium-glucose cotransporter 2-inhibitors.J Am Soc Nephrol. 2020; 31: 907-919Crossref PubMed Scopus (80) Google Scholar,4Packer M. Critical reanalysis of the mechanisms underlying the cardiorenal benefits of SGLT2 inhibitors and reaffirmation of the nutrient deprivation signaling/autophagy hypothesis.Circulation. 2022; 146: 1383-1405Crossref PubMed Scopus (136) Google Scholar This metabolic task is lost in chronic kidney disease, but it is restored by SGLT2 inhibitors through their ability to upregulate SIRT1 signaling, thus redirecting glucose away from anabolism, and promoting the oxidation of fatty acids and glucose to enhance the production of ATP. The ability to produce ATP action is facilitated by an effect of SIRT1 and AMPK to restore mitochondrial health through actions to reduce oxidative stress, enhance mitophagy, and augment mitochondrial biogenesis.4Packer M. Critical reanalysis of the mechanisms underlying the cardiorenal benefits of SGLT2 inhibitors and reaffirmation of the nutrient deprivation signaling/autophagy hypothesis.Circulation. 2022; 146: 1383-1405Crossref PubMed Scopus (136) Google Scholar At the same time, SGLT2 inhibitors suppress signaling through mTOR and HIF-1α, further mitigating oxidative stress and acting to mute proinflammatory and profibrotic pathways in glomerular podocytes and mesangial cells and in the proximal tubule. There is considerable experimental evidence to support an effect of SGLT2 inhibitors to restore cytoprotective signaling as the primary mechanism underlying their renoprotective effects (Figure 1). Using single-cell RNA-sequencing analysis of the kidneys of diabetic mice, Wu et al.5Wu H. Gonzalez Villalobos R. Yao X. et al.Mapping the single-cell transcriptomic response of murine diabetic kidney disease to therapies.Cell Metab. 2022; 34: 1064-1078Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar demonstrated that SGLT2 inhibitors induce a state of fasting mimicry and hypoxia in the proximal renal tubule by restoring the splicing of master genes that are responsible for health cellular metabolism. Inoue et al.6Inoue M.K. Matsunaga Y. Nakatsu Y. et al.Possible involvement of normalized Pin1 expression level and AMPK activation in the molecular mechanisms underlying renal protective effects of SGLT2 inhibitors in mice.Diabetol Metab Syndr. 2019; 11: 57Crossref Scopus (45) Google Scholar showed that canagliflozin reduced mesangial cell proliferation and peritubular fibrosis; these effects were accompanied by increased AMPK phosphorylation, and the benefits of SGLT2 inhibition were abrogated by AMPK inhibition. Liu et al.7Liu X. Xu C. Xu L. et al.Empagliflozin improves diabetic renal tubular injury by alleviating mitochondrial fission via AMPK/SP1/PGAM5 pathway.Metabolism. 2020; 111154334Abstract Full Text Full Text PDF Scopus (61) Google Scholar reported that empagliflozin reduced oxidative stress, mitochondrial dysfunction, and apoptosis in proximal tubular cells exposed to high glucose; these effects were accompanied by upregulation of AMPK and were abrogated by AMPK inhibition. Using a similar model, Xu et al.8Xu J. Kitada M. Ogura Y. et al.Dapagliflozin restores impaired autophagy and suppresses inflammation in high glucose-treated HK-2 cells.Cells. 2021; 10: 1457Crossref PubMed Scopus (64) Google Scholar observed that dapagliflozin reduced proinflammatory signaling and increased AMPK phosphorylation; the benefits of SGLT2 inhibitors were eliminated by AMPK inhibition. Zhang et al.9Zhang Z. Ni L. Zhang L. et al.Empagliflozin regulates the AdipoR1/p-AMPK/p-ACC pathway to alleviate lipid deposition in diabetic nephropathy.Diabetes Metab Syndr Obes. 2021; 14: 227-240Crossref PubMed Scopus (25) Google Scholar showed that empagliflozin reduced interstitial fibrosis in murine diabetic nephropathy; this benefit was accompanied by increased AMPK phosphorylation and abolished by AMPK inhibition. Park et al.10Park C.H. Lee B. Han M. et al.Canagliflozin protects against cisplatin-induced acute kidney injury by AMPK-mediated autophagy in renal proximal tubular cells.Cell Death Discov. 2022; 8: 12Crossref Scopus (21) Google Scholar noted that canagliflozin increased cell viability and prevented cellular injury in HK2 proximal tubular cells exposed to cisplatin, and these benefits were abolished by AMPK inhibition. Yang et al.11Yang L. Liang B. Li J. et al.Dapagliflozin alleviates advanced glycation end product induced podocyte injury through AMPK/mTOR mediated autophagy pathway.Cell Signal. 2022; 90110206Crossref Scopus (25) Google Scholar showed that dapagliflozin reduced proinflammatory signaling and apoptosis in cultured podocytes exposed to advanced glycation end products; these effects were accompanied by increased AMPK phosphorylation and abrogated by AMPK inhibition. Importantly, in the reports by Xu et al.,8Xu J. Kitada M. Ogura Y. et al.Dapagliflozin restores impaired autophagy and suppresses inflammation in high glucose-treated HK-2 cells.Cells. 2021; 10: 1457Crossref PubMed Scopus (64) Google Scholar Park et al.10Park C.H. Lee B. Han M. et al.Canagliflozin protects against cisplatin-induced acute kidney injury by AMPK-mediated autophagy in renal proximal tubular cells.Cell Death Discov. 2022; 8: 12Crossref Scopus (21) Google Scholar and Yang et al.,11Yang L. Liang B. Li J. et al.Dapagliflozin alleviates advanced glycation end product induced podocyte injury through AMPK/mTOR mediated autophagy pathway.Cell Signal. 2022; 90110206Crossref Scopus (25) Google Scholar the favorable effects of SGLT2 inhibitors were also abolished by pharmacologic silencing of autophagic flux and mitophagy, thus identifying a key adaptive mechanism by which enhanced nutrient deprivation signaling might exert cytoprotective effects.4Packer M. Critical reanalysis of the mechanisms underlying the cardiorenal benefits of SGLT2 inhibitors and reaffirmation of the nutrient deprivation signaling/autophagy hypothesis.Circulation. 2022; 146: 1383-1405Crossref PubMed Scopus (136) Google Scholar These experiments demonstrating that the effects of SGLT2 inhibitors are mediated by upregulation of SIRT1 and AMPK are paralleled by experiments reporting that SGLT2 inhibitors suppress mTOR/HIF-1α signaling. Li et al.12Li J. Liu H. Takagi S. et al.Renal protective effects of empagliflozin via inhibition of EMT and aberrant glycolysis in proximal tubules.JCI Insight. 2020; 5e129034Crossref Scopus (136) Google Scholar showed that high-glucose media induced endothelial-mesenchymal transition, which was accompanied by suppression of SIRT signaling, upregulation of HIF-1α, and aberrant glycolysis. SGLT2 knockdown reversed these abnormalities and inhibited the mesenchymal transition of proximal tubular cells and neighboring endothelial cells. Kogot-Levin et al.3Kogot-Levin A. Hinden L. Riahi Y. et al.Proximal tubule mTORC1 is a central player in the pathophysiology of diabetic nephropathy and its correction by SGLT2 inhibitors.Cell Rep. 2020; 32107954Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar noted that dapagliflozin inhibited peritubular fibrosis and preserved glomerular function in a mouse model of diabetic nephropathy; these benefits were accompanied by suppression of mTOR activation, and the benefits of SGLT2 inhibitors were abolished by constitutive overactivation of mTOR. Tomita et al.13Tomita I. Kume S. Sugahara S. et al.SGLT2 inhibition mediates protection from diabetic kidney disease by promoting ketone body-induced mTORC1 inhibition.Cell Metab. 2020; 32: 404-419.e6Abstract Full Text Full Text PDF PubMed Scopus (195) Google Scholar demonstrated the importance of mTOR suppression in several models of chronic kidney disease. Empaglifozin prevented podocyte and tubulointerstitial lesions while inhibiting mTOR signaling in nondiabetic chronic kidney disease produced in 5/6 nephrectomized mice. In proximal tubular cells of ApoE-deficient mice subjected to a high-fat diet, mTOR hyperactivation played a critical role in mediating the progression of chronic kidney disease, but this effect was abolished by empagliflozin. Interestingly, the favorable effects of empagliflozin were mimicked by 1,3-butanediol, a ketone body precursor, and the renoprotective effects of empagliflozin were prevented by knockout of 3-hydroxy-3-methylglutaryl-coenzyme A synthase 2, the rate-limiting enzyme for ketogenesis. These observations suggested that ketone bodies produced by SGLT2 inhibitors as an effect of starvation mimicry may help to mediate their effects on nutrient surplus and nutrient deprivation signaling. Other investigators have also proposed that ketone bodies may function as metabolic signaling molecules (acting to upregulate SIRT1 and downregulate mTOR) rather than serving as an alternative fuel for the production of ATP.2Packer M. Role of impaired nutrient and oxygen deprivation signaling and deficient autophagic flux in diabetic CKD development: implications for understanding the effects of sodium-glucose cotransporter 2-inhibitors.J Am Soc Nephrol. 2020; 31: 907-919Crossref PubMed Scopus (80) Google Scholar,4Packer M. Critical reanalysis of the mechanisms underlying the cardiorenal benefits of SGLT2 inhibitors and reaffirmation of the nutrient deprivation signaling/autophagy hypothesis.Circulation. 2022; 146: 1383-1405Crossref PubMed Scopus (136) Google Scholar In fact, in the report by Tomita et al.,13Tomita I. Kume S. Sugahara S. et al.SGLT2 inhibition mediates protection from diabetic kidney disease by promoting ketone body-induced mTORC1 inhibition.Cell Metab. 2020; 32: 404-419.e6Abstract Full Text Full Text PDF PubMed Scopus (195) Google Scholar the increase in proximal tubular ATP production following 1,3-butanediol was related to enhanced oxidation of long-chain fatty acids (rather than ketolysis), the expected result if restoration of cellular energetics was due to an improvement in mitochondrial function. Importantly, these effects have been demonstrated not only in animal models, but in cultured cells, which are not subject to hemodynamic perturbations. It is understood that many nephrologists believe that SGLT2 inhibitors exert renoprotective effects by increasing sodium delivery to the distal nephron and macula densa. The enhanced distal delivery of sodium has been hypothesized to increase distal tubular workload, leading to hypoxia at the corticomedullary junction. Furthermore, the augmented delivery to the macula densa might activate tubuloglomerular feedback and reduce intraglomerular filtration pressures, which has been proposed to slow the evolution of chronic kidney disease. However, the results of clinical and experimental studies do not support the pathophysiological importance of these hemodynamic changes. SGLT2 inhibitors do not produce renal medullary hypoxia in patients without diabetes14Zanchi A. Burnier M. Muller M.E. et al.Acute and chronic effects of SGLT2 inhibitor empagliflozin on renal oxygenation and blood pressure control in nondiabetic normotensive subjects: a randomized, placebo-controlled trial.J Am Heart Assoc. 2020; 9e016173Crossref Scopus (63) Google Scholar; instead, the source of increased erythropoietin production and erythrocytosis following SGLT2 inhibition appears to be the activation of SIRT1, which leads to increased expression of hypoxic-inducible factor-2α and erythropoietin production, not only in the kidney but also in the liver. Furthermore, although alleviation of glomerular hyperfiltration might exert renoprotective effects in states of hyperfiltration (i.e., diabetes), patients with heart failure do not have glomerular hyperfiltration, but nevertheless, they show a reduction in major adverse renal outcomes with SGLT2 inhibitors in large-scale trials. Interestingly, the finding of a short-term decline in glomerular filtration rate following initiation of SGLT2 inhibitors may be explained by an effect of AMPK upregulation to enhance tubuloglomerular feedback rather than an effect on distal tubular sodium delivery.15Huang D.Y. Gao H. Boini K.M. et al.In vivo stimulation of AMP-activated protein kinase enhanced tubuloglomerular feedback but reduced tubular sodium transport during high dietary NaCl intake.Pflugers Arch. 2010; 460: 187-196Crossref Scopus (16) Google Scholar Taken together, there is a critical mass of experimental evidence that supports a renoprotective effect of SGLT2 inhibitors, which is mediated by upregulation of SIRT/1AMPK and downregulation of mTOR/HIF-1α in the proximal tubule and in glomerular podocytes and mesangial cells. These drugs exert consistent effects to mute oxidative stress, restore mitochondrial health, mitigate proinflammatory and profibrotic signaling, and prevent cell death, thus maintaining the normal architecture and physiology of the kidney. Importantly, in numerous experimental studies, these renoprotective effects are abolished if SIRT1/AMPK/autophagy is silenced or if mTOR is overactivated. Therefore, SGLT2 inhibitors act as modulators of nutrient deprivation and nutrient surplus signaling to restore healthy proximal renal tubular homeostasis and metabolism. All the authors declared no competing interests. SGLT2 inhibitor: 2-way superstar in nephrology?Kidney InternationalVol. 105Issue 6PreviewShohei Ohtani became an amazing 2-way player in a modern-day game of baseball that basically never sees them, and he won his second American League most valuable player award unanimously in 2023. Full-Text PDF Kidney protective mechanisms of SGLT2 inhibitors: evidence for a hemodynamic effectKidney InternationalVol. 105Issue 6PreviewSodium-glucose cotransporter-2 (SGLT2) inhibitors were introduced a decade ago for the treatment of type 2 diabetes (T2D) and have emerged as a key therapy for the treatment of chronic kidney disease (CKD). In trials with primary kidney end points, SGLT2 inhibitors reduced the composite of kidney failure, kidney death, and doubling of serum creatinine by 28% to 39%.1 Benefits of this class of medication are independent of glycemic lowering, as glucose lowering with other drug classes has not been associated with similar improvements in kidney outcomes. Full-Text PDF