Prolidase (peptidase D), encoded by the PEPD gene, is a ubiquitously expressed cytosolic metalloproteinase, the only enzyme capable of cleaving imidodipeptides containing C-terminal proline or hydroxyproline. Prolidase catalyzes the rate-limiting step during collagen recycling and is essential in protein metabolism, collagen turnover, and matrix remodeling. Prolidase, therefore plays a crucial role in several physiological processes such as wound healing, inflammation, angiogenesis, cell proliferation, and carcinogenesis. Accordingly, mutations leading to loss of prolidase catalytic activity result in prolidase deficiency a rare autosomal recessive metabolic disorder characterized by defective wound healing. In addition, alterations in prolidase enzyme activity have been documented in numerous pathological conditions, making prolidase a useful biochemical marker to measure disease severity. Furthermore, recent studies underscore the importance of a non-enzymatic role of prolidase in cell regulation and infectious disease. This review aims to provide comprehensive information on prolidase, from its discovery to its role in health and disease, while addressing the current knowledge gaps.

FOXG1 Syndrome (FS) is a devastating neurodevelopmental disorder that is caused by a heterozygous loss-of-function (LOF) mutation of the FOXG1 gene, which encodes a transcriptional regulator important for telencephalic brain development. People with FS have marked developmental delays, impaired ambulation, movement disorders, seizures, and behavior abnormalities including autistic features. Current therapeutic approaches are entirely symptomatic, however the ability to rescue phenotypes in mouse models of other genetic neurodevelopmental disorders such as Rett syndrome, Angelman syndrome, and Phelan-McDermid syndrome by postnatal expression of gene products has led to hope that similar approaches could help modify the disease course in other neurodevelopmental disorders such as FS. While FoxG1 protein function plays a critical role in embryonic brain development, the ongoing adult expression of FoxG1 and behavioral phenotypes that present when FoxG1 function is removed postnatally provides support for opportunity for improvement with postnatal treatment. Here we generated a new mouse allele of Foxg1 that disrupts protein expression and characterized the behavioral and structural brain phenotypes in heterozygous mutant animals. These mutant animals display changes in locomotor behavior, gait, anxiety, social interaction, aggression, and learning and memory compared to littermate controls. Additionally, they have structural brain abnormalities reminiscent of people with FS. This information provides a framework for future studies to evaluate the potential for post-natal expression of FoxG1 to modify the disease course in this severe neurodevelopmental disorder.

Prolidase (PEPD) is a ubiquitously expressed cytosolic dipeptidase that has the unique ability to cleave proline or hydroxyproline on the C‐terminus of imidodipeptides and imidotripeptides. The reaction is vital for collagen degradation. Since collagen is the most abundant protein in the body, our objective is to get a better understanding of the enzymes involved in its turnover is crucial. In silico analysis on prolidase promoter showed that putative transcription factor of interest is KLF6. To test the hypothesis that the expression of PEPD gene may be regulated by the binding of the transcription factor KLF6 to candidate binding sites we used chromatin immunoprecipitation (ChIP) assay. HEK293T cells were transfected with FLAG‐hKLF6 plasmid and the cellular lysates were obtained to measure the KLF6 protein expression by immunoblotting. After that, purified DNA from the ChIP assays were used in end‐point PCR with primers targeting candidate KLF6‐binding sites in PEPD promoter. The primers used were expected to yield a 615 bp amplicon. PCR products were resolved on 1% agarose/TAE gel. The second round of PCR was performed in which endpoint PCR products from the first round of PCR were used as a template for nested PCR with primers designed to amplify 164 bp. Nevertheless, our results showed no detectable PEPD promoter‐specific signals in the PCR analysis of the ChIP products. However, due to the inherent caveats in the experimental design, choice of reagents, and analysis method, it would be premature to conclude at this time point that PEPD expression is not regulated by KLF6. Accordingly, the design of future experiments will effectively address the limitations of this current work and will help reveal the identity of transcription factors regulating PEPD expression. Support or Funding Information Supported by National Institutes of Health (NIH) Grants DA037779 and MD007586 (to Jui Pandhare) and DA024558, DA30896, DA033892, DA021471, AI22960 and MD007586 (to Chandravanu Dash). Ireti Eni‐Aganga is supported by RISE Grant. The work is also supported by the RCMI Grant G12MD007586, the Vanderbilt CTSA Grant UL1RR024975, the Meharry Translational Research Center (MeTRC) CTSA grant (U54 RR026140 from NCRR/NIH, the U54 Grant MD007593 from NIMHD/NIH, and the Tennessee Center for AIDS Research (P30 AI110527).

Prolidase, a cytosolic exopeptidase, and a member of the matrix metalloproteinase (MMP) family, is encoded by the PEPD gene in humans. Since Prolidase is the only enzyme which can cleave dipeptides containing C‐terminal proline, or hydroxyproline, it plays an essential role in protein metabolism, collagen turnover, and matrix remodeling. Prolidase is essential in several physiological and pathological processes such as wound healing, inflammation, angiogenesis, cell proliferation, and carcinogenesis. Surprisingly, little is known about the molecular and cellular regulation of PEPD gene expression. In initial studies, we observed a dense CG‐rich portion around the transcription start site, suggesting a possible role of promoter methylation in the transcriptional regulation of PEPD gene. To study the transcriptional regulation of PEPD gene, we cloned and characterized the human PEPD promoter. The PEPD promoter was amplified from the human genome via PCR and inserted into a luciferase reporter construct. As demonstrated in our results, increase in luciferase activity was obtained after transfection of the PEPD luciferase reporter in HEK293T, indicating the successful construction of the luciferase reporter. Next, we performed in vitro methylation of the PEPD promoter using SssI methyltransferase which methylates DNA CpG islands. Methylation was confirmed by BstUI digestion that cleaves at unmethylated CpG dinucleotides but not at methylated CpG. The CpG methylation significantly inhibited PEPD promoter activity in comparison to the unmethylated construct. Taken together, we believe, these results will generate new knowledge on the molecular regulation of prolidase and provide better insight in our understanding of regulation of prolidase expression in various physiological and pathological conditions.Support or Funding InformationSupported by National Institutes of Health (NIH) Grants DA037779 and MD007586 (to Jui Pandhare) and DA024558, DA30896, DA033892, DA021471, AI22960 and MD007586 (to Chandravanu Dash). Ireti Eni‐Aganga is supported by RISE Grant. The work is also supported by the RCMI Grant G12MD007586, the Vanderbilt CTSA Grant UL1RR024975, the Meharry Translational Research Center (MeTRC) CTSA grant (U54 RR026140 from NCRR/NIH, the U54 Grant MD007593 from NIMHD/NIH, and the Tennessee Center for AIDS Research (P30 AI110527).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Prolidase, also known as peptidase D (PEPD), is a hydrolase that cleaves dipeptides containing C‐terminal proline or hydroxyproline. These dipeptides are generated largely during collagen turnover, therefore prolidase catalysis is an essential rate‐limiting step during collagen biosynthesis. Consequently, prolidase plays a significant role in collagen metabolism, matrix remodeling, and wound healing. Defective wound healing is one of the hallmarks of Prolidase Deficiency, a rare autosomal recessive disorder characterized by the excretion of prolidase substrates in the urine. Although prolidase is implicated in wound healing, its molecular and cellular regulation remains understudied. Our initial in silico analysis of the PEPD promoter (PEPDpro) identified key regulatory elements upstream of the transcription start site. We identified Kruppel‐like factor 6 (KLF6), a zinc‐finger transcription factor associated with vascular injury, wound healing, and collagen metabolism. To study the interaction between KLF6 and prolidase, we amplified the promoter from the human genome and inserted it into a luciferase reporter construct. Our preliminary data demonstrate that KLF6 enhances PEPD promoter activity in a dose‐dependent manner. Additionally, KLF6 is regulated by transforming growth factor β1 (TGFβ1), and our data illustrate that TGFβ1 drives PEPD promoter activity. These results will generate new knowledge on the molecular regulation of prolidase and aid in developing therapeutic approaches to regulate prolidase expression in various physiological and pathological conditions such as wound healing.