Prabhleen Singh Research

The research in the Singh Lab is aimed at understanding the early determinants of progression after acute or chronic injury. Our lab focuses on the coupling of epithelial tubular transport and mitochondrial metabolism, and novel regulators of these processes. Our particular interest is in tubular mitochondrial (dys)function in the initiation and progression of injury. We have provided new insights into early hyperfiltration and aberrant tubuloglomerular feedback responses in disease progression. Our research has also demonstrated early tubular hypermetabolism and mitochondrial dysfunction in CKD. We utilize classical physiological techniques to measure renal hemodynamics, oxygenation, glomerular and tubular function. To complement these in-vivo techniques, we employ novel molecular approaches to assess tubular metabolism and mitochondrial bioenergetics. Current projects include assessment of intrarenal hemodynamics along with determinants of oxygen utilization and mitochondrial function in tubular segments in models of AKI including ischemia reperfusion and cecal ligation and puncture model of sepsis and models of diabetic and non-diabetic CKD.

Renal oxygenation and metabolism in CKD

CKD is a highly prevalent condition with high morbidity and mortality and inexorable progression to end stage renal disease. Chronic tissue hypoxia has been identified as a major culprit in CKD progression and validated by several investigators in experimental and human CKD. Hence, it is imperative to understand the regulation of kidney oxygenation in CKD to identify novel therapeutic targets. Our lab has investigated the regulation of renal oxygenation and mitochondrial metabolism in CKD by hypoxia inducible factor-1α (HIF-1α) and AMP activated kinase (AMPK). We have highlighted novel interactions between these regulators of tubular metabolism and mitochondrial function and the molecular mechanisms by which they facilitate cellular hypoxia adaptation and improve renal function in kidney disease.

Publications:

• Singh P, Ricksten SE, Bragadottir G, Redfors B, Nordquist L. Renal oxygenation and hemodynamics in acute kidney injury and chronic kidney disease. Clin Exp Pharmacol Physiol. 2013 Feb;40(2):138-47
• Li H, Satriano J, Thomas J, Miyamoto S, Sharma K, Pastor-Soler NM, Hallows KR, Singh P. Interactions between HIF-1α and AMPK in the regulation of cellular hypoxia adaptation in chronic kidney disease. Am J Physiol Renal Physiol. 2015 Sep 1;309(5):F414-28. Epub 2015 Jul 1. PubMed Central PMCID: PMC4556888.
• Thomas JL, Pham H, Li Y, Hall E, Perkins GA, Ali SS, Patel HH, Singh P. Hypoxia-inducible factor-1α activation improves renal oxygenation and mitochondrial function in early chronic kidney disease. Am J Physiol Renal Physiol. 2017 Aug 1;313(2):F282-F290. PubMed Central PMCID: PMC5582905

Renal hemodynamics and metabolism in acute kidney injury

AKI in the setting of sepsis is frequently observed and is a significant clinical problem. Yet, therapeutic strategies have been generic, ineffective and largely supportive. The lack of complete understanding of its pathogenesis has been identified as a significant barrier to progress in the field. Renal hemodynamics and metabolism play an important role in the pathophysiology of AKI in sepsis. We have studied sepsis-associated AKI using the clinically relevant cecal ligation and puncture (CLP) model in rodents. We observed a significant reduction in GFR and filtration fraction with nearly preserved renal blood flow. Additional investigations have revealed increased renal oxygen consumption despite a decreased need for ATP and evidence for early mitochondrial dysfunction. This is an active area of ongoing research in the lab.

Publications:

• Blantz RC, Singh P. Pre-renal contributions to acute kidney injury. Invited review. Controversies in AKI. Contrib Nephrol. 2011;174:4-11. Epub 2011 Sep 9.
• Nourbakhsh N, Singh P. Role of renal oxygenation and mitochondrial function in the pathophysiology of acute kidney injury. Nephron Clin Pract 2014; 127:149-152. PMCID: PMC5540439
• Hepokoski M, Englert JA, Baron RM, Crotty-Alexander L, Fuster MM, Beitler JR, Malhotra A, Singh P. Ventilator Induced Lung Injury Increases Expression of Endothelial Inflammatory Mediators in the Kidney. Am J Physiol Renal Physiol. 2017 Apr 1;312(4):F654-F660. Epub 2016 Nov 9. PMCID: PMC5407070
• Bullen A, Liu ZZ, Hepokoski M, Li Y, Singh P. Renal Oxygenation and Hemodynamics in Kidney Injury. Nephron. 2017;137(4):260-263. Epub 2017 Jun 15. PMCID: PMC5732093

Interactions between CKD and AKI

Clinical observations suggest CKD is a risk factor for AKI. Our investigations into the pathophysiology of early CKD using the subtotal nephrectomy (STN) rodent model revealed remarkable hemodynamics and metabolic adaptations in the diseased kidney. We discovered that normal tubuloglomerular feedback (TGF) activity in the STN kidney was obliterated. We investigated the consequences of this atypical TGF response in STN when subjected to AKI. Remarkably, the diseased kidney was resistant to subsequent injury when subjected to ischemia reperfusion and TGF plays an important role in this functional resilience. In addition, we demonstrated the cytoprotective effects of hypoxia inducible factor-1α (HIF-1α) in this response. Whether these pre-conditioning mechanisms are operative in in later stages of STN, and how pre-existing changes in renal metabolism impact recovery from AKI is not known. This is an active area of ongoing research in the lab.

Publications:

• Singh P, Deng A, Blantz RC, Thomson SC. Unexpected effect of angiotensin AT-1 receptor blockade on tubuloglomerular feedback in early subtotal nephrectomy. Am J Physiol Renal Physiol. 2009 May; 296(5): F1158-65. Epub 2009 Feb 11. PMCID: PMC2681370
• Singh P, Rifkin DE, Blantz, RC. Chronic kidney disease: An inherent risk factor for acute kidney injury? Clin J Am Soc Nephrol. 2010 Sep;5(9):1690-5. Epub 2010 Aug 5.
• Singh P, Blantz RC, Rosenberger C, Gabbai FB, Schoeb TR, Thomson SC. Aberrant Tubuloglomerular Feedback and HIF-1α Confer Resistance to Ischemia after Subtotal Nephrectomy. J Am Soc Nephrol. 2012 Mar;23(3):483-93. Epub 2012 Jan 19. PMCID: PMC3294306.
• Singh P, Thomson SC. Salt Sensitivity of Tubuloglomerular Feedback in the Early Remnant Kidney. Am J Physiol Renal Physiol. Am J Physiol Renal Physiol. 2014 Jan;306(2):F172-80. PMCID: PMC3920016

Glomerular and Tubular Function in Early Diabetes

Early diabetic kidney is characterized by structural and functional changes that have a lasting impact on the development of overt diabetic nephropathy. We have examined epithelial transport and metabolism in the diabetic kidney using the streptozotocin (STZ) model of type 1 diabetes in rats. The proximal tubular hyperreabsorption in diabetes is largely mediated by sodium glucose co-transporter (SGLT2). We have recently described the glomerular and tubular effects of new diabetic treatments currently in clinical use including SGLT2 inhibitors and glucagon-like peptide 1 (GLP1) agonists. Renal micropuncture experiments in early diabetic rats, demonstrated a significant reduction in proximal tubular reabsorption and SNGFR with SGLT2 blockade. We have also examined the effects of GLP1 receptor agonist, exenatide, on SNGFR and proximal tubular reabsorption and demonstrated the novel effects of GLP1 activation as a renal vasodilator and proximal diuretic. Ongoing investigations include the impact of SGLT2 inhibition and GLP1 activation on renal oxygen consumption and mitochondrial function in early diabetes.

Publications:

• Thomson SC, Rieg T, Miracle CM, Mansoury H, Whaley J, Vallon V, Singh P. Effects of chronic SGLT2 blockade on glomerular and tubular function in the early diabetic rat. Am J Physiol Regul Integr Comp Physiol. 2012 Jan;302(1):R75-83. Epub 2011 Sep 21. PMCID: PMC3349378
• Thomson SC, Kashkouli A, Singh P. Glucagon-like peptide 1 receptor stimulation increases GFR and suppresses proximal reabsorption in the rat. Am J Physiol Renal Physiol. 2013 Jan 15;304(2):F137-44. Epub 2012 Sep 26. PMCID: PMC3543628
• Liu ZZ, Bullen A, Li Y, Singh P. Renal Oxygenation in the pathophysiology of chronic kidney disease. Front Physiol. 2017 Jun 28;8:385. PubMed Central PMCID: PMC5487476.
• Thomson SC, Kashkouli A, Liu ZZ, Singh P. Renal hemodynamic effects of glucagon like peptide-1 agonist are mediated by nitric oxide but not prostaglandin. Am J Physiol Renal Physiol. 2017 Oct 1;313(4):F854-F858. Epub 2017 Jul 19. PMCID: PMC5668591