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Gregory G. Germino, M.D.

Photo of Gregory Germino
Scientific Focus Areas: Cell Biology, Genetics and Genomics, Molecular Biology and Biochemistry, Systems Biology

Professional Experience

  • Senior Investigator, Kidney Diseases Branch, NIDDK, NIH, 2009–Present
  • Adjunct Professor of Medicine, Johns Hopkins University School of Medicine, 2009–Present
  • Professor of Medicine, Division of Nephrology, Johns Hopkins University School of Medicine, 2003–2009
  • Affiliate Member, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, 2002–2009
  • Joint Appointment, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, 2001–2009
  • Associate Professor of Medicine, Division of Nephrology, Johns Hopkins University School of Medicine, 1997–2003
  • Assistant Professor of Medicine, Division of Nephrology, Johns Hopkins University School of Medicine, 1992–1997
  • Associate Research Scientist, Instructor and Assistant Professor, Yale University School of Medicine, 1988–1992
  • Research Post-Doctoral Fellow, Nuffield Department of Medicine, Oxford University, 1987–1988
  • Clinical Post-Doctoral Fellow, Nephrology, Yale University School of Medicine, 1986–1987
  • Internal Medicine Residency, Yale–New Haven Hospital, 1983–1986
  • M.D., University of Chicago Pritzker School of Medicine, 1983
  • B.S., Loyola University of Chicago, 1979

Research Goal

The purpose of our research is to understand how mutations of PKD genes cause polycystic kidney disease.

Current Research

The function of the kidney critically depends on the proper structure of its tubule system, yet regulation of tubular diameter is a poorly understood phenomenon. Cystic diseases of the kidney offer unique opportunities to study these processes. My research focuses on the molecular basis of renal cystic disease and renal tubular morphogenesis.

Autosomal dominant polycystic kidney disease (ADPKD) affects approximately 1/1000 Americans. Cysts arise at all stages of life, and gradually expand to replace normal renal parenchyma. This process results in end stage kidney failure (ESKF) in approximately half by the 6th decade, accounting for approximately 5 percent of all cases of ESKF. Autosomal recessive polycystic kidney disease (ARPKD) is rare (1/20,000) but often more severe. Therapies for both are limited to managing the complications. We have, however, made great progress in understanding their pathobiology and the role of the normal PKD gene products in regulating tubular morphology.

Mutations in either of two genes, PKD1 and PKD2, cause most forms of ADPKD. Mutations appear to compromise gene function, and much data implicate a molecular recessive model as responsible for initiating cyst growth. PKD1 and PKD2 encode components of a receptor-channel complex that likely has ciliary and non-ciliary functions. Using orthologous mouse models, we have demonstrated unsuspected, complex development-stage specific consequences of Pkd1 inactivation that are linked to metabolic pathways. These models also have been used to show that PKD genes are essential for proper form and function of multiple other organs. We are pursuing several parallel lines of inquiry regarding the relationship between PKD proteins, cellular metabolism, matrix, and planar cell polarity pathways.

ARPKD is a second interest. We identified the gene mutated in this disorder, PKHD1, and have shown that it likely encodes a very large membrane-associated protein that undergoes Notch-like proteolytic processing. We have developed a series of mouse lines and cell culture systems to model the disease and study the protein, and we have shown genetic interaction between the PKD1 and PKHD1 loci. Current efforts are focused on determining its function in kidney and liver development.

Applying our Research

PKD is one of the most common, serious mendelian disorders of man and causes 4-5 percent of all end stage kidney disease in the United States. Affected individuals also suffer from other complications such as hypertension, cyst infections, abdominal pain, and have an increased risk of intracranial aneurysms. Present management is focused on treating symptoms. Understanding the mechanisms of disease will allow us to develop safe and effective treatments.

Need for Further Study

While the PKD gene products polycystin 1 (PC1) and polycystin 2 (PC2) are essential for establishing and maintaining normal tubule structure, we do not know how they do this. Several lines of evidence suggest that they function as a receptor-channel complex, but what they sense and signal is poorly understood. Though numerous pathways have been reported to be dysregulated in cystic epithelia, it is unclear how these link back to the function of the PC1/PC2 complex, which pathways are dysregulated at the earliest stages of cyst formation, and which are altered as secondary consequence of cystic dilations. We also do not understand why cysts form immediately after gene inactivation in young mice but take months to arise in older animals. What factors preserve tubular structure during this interval, and what triggers the subsequent failure? Understanding these processes is important not only from a pathobiological standpoint, but also to design more specific therapies. We also need better tools for assessing the progression of disease so we can better evaluate the effectiveness of clinical interventions.

Select Publications

A cleavage product of Polycystin-1 is a mitochondrial matrix protein that affects mitochondria morphology and function when heterologously expressed.
Lin CC, Kurashige M, Liu Y, Terabayashi T, Ishimoto Y, Wang T, Choudhary V, Hobbs R, Liu LK, Lee PH, Outeda P, Zhou F, Restifo NP, Watnick T, Kawano H, Horie S, Prinz W, Xu H, Menezes LF, Germino GG.
Sci Rep (2018 Feb 9) 8:2743. Abstract/Full Text
Fatty Acid Oxidation is Impaired in An Orthologous Mouse Model of Autosomal Dominant Polycystic Kidney Disease.
Menezes LF, Lin CC, Zhou F, Germino GG.
EBioMedicine (2016 Mar) 5:183-92. Abstract/Full Text
View More Publications

Research in Plain Language

The kidney is made up of millions of filter units and tubes that work together to rid our body of waste and to manage our fluids and electrolytes. Processes that alter the function of either the filters or the tubes can cause the kidneys to stop functioning properly. My research is focused on a set of conditions that causes cysts to form inside the kidney. Cysts are balloon-like structures filled with fluid that form from kidney tubes. While a few are common in the kidney as people age, kidneys fail when the cysts become too numerous or too large. Autosomal dominant (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) are hereditary conditions that can cause kidney failure due to kidney cysts. Polycystic kidney disease (PKD) affects 1/1000 people and is the fourth most common cause of kidney failure in the United States. Currently available therapies mostly treat symptoms, though one newly approved drug may slow progression.

Scientists do not understand how mutations in PKD genes lead to the formation of cysts. To develop better treatments, we must determine what the genes do and how they regulate tube size. We must also determine the factors that promote the growth of cysts so we can identify ways to safely block this. My laboratory is focused on addressing these gaps in our knowledge using experimental models and methods from multiple scientific discipines like systems biology, cell biology, molecular genetics and biochemistry. Our long-term goal is to use this information to guide development of therapies that prevent and treat cystic disease.

Research Images