trade-offs

Right, you're asking about the trade-offs between different approaches to aging. The allotopic expression strategy has some distinct advantages over other interventions, but also faces unique challenges.

On the advantages side, allotopic expression directly addresses root causes of aging rather than symptoms. While senolytics clear zombie cells after they form and caloric restriction merely slows damage accumulation, allotopic expression prevents mitochondrial dysfunction from occurring at all. The Longevity Research Institute has achieved expression of an essential mitochondrial gene in the nucleus and proper functioning of the protein. Allotopic ATP8 was able to compete with mitochondrial ATP8 even in wild-type mice and outperformed the mutant ATP8. The allotopic gene functioned well in the genetically modified mice's offspring for at least four generations, with no adverse effects on fertility.

The permanence factor is crucial. Engineering "backup copies" of the mutation-prone mitochondrial genes into the safe harbor of the nucleus is our strongest strategy for protecting the body from large mitochondrial deletion mutations. Once installed, these nuclear backups provide protection for the cell's lifetime, unlike drugs like rapamycin that require continuous administration. Based on calorie restriction research, there have been attempts to develop drugs that will have the same effect on the aging process as a CR diet, known as caloric restriction mimetic drugs, such as rapamycin and metformin. But these still need constant dosing.

Compared to broader genetic engineering approaches, allotopic expression is more targeted and less risky. CRISPR-Cas genome editing technology offers groundbreaking potential for restoring the vitality of aged stem cells. As stem cells age, their regenerative capacity declines due to accumulated genetic and epigenetic changes. Using CRISPR-Cas, scientists can directly edit these changes or modulate aging-related pathways. But wholesale genetic modification carries unpredictable risks. Allotopic expression only adds backup copies without altering existing genes.

The disadvantages? Technical difficulty stands out. In the present study, allotopic expression of three different mtDNA-coded polypeptides (ATPase8, apocytochrome b, and ND4) into COS-7 and HeLa cells was analyzed. Among these, only ATPase8 was correctly expressed and localized to mitochondria. Our observations suggest that only a subset of mitochondrial genes can be replaced allotopically. The hydrophobicity of many mitochondrial proteins makes them incredibly difficult to import back into mitochondria after nuclear expression.

Cost and complexity dwarf simpler interventions. Caloric restriction costs nothing. Senolytics like dasatinib plus quercetin are already FDA-approved drugs. Gene therapy for allotopic expression requires sophisticated viral vectors and precise genetic engineering. The researchers utilized the CRISPR/Cas9 system to deliver the gene therapy into the cells of the progeria mouse model. An adeno-associated virus (AAV) was injected containing two synthetic guide RNAs and a reporter gene. The guide RNA ushers the Cas9 protein to a specific location on the DNA where it can make a cut.

The scope limitation is significant. Mitochondrial mutations represent just one of my seven SENS damage categories. Even perfect allotopic expression wouldn't address senescent cells, crosslinks, or other damage types. In contrast, partial reprogramming potentially reverses multiple aging hallmarks simultaneously. Reprogramming-induced rejuvenation strategies have begun to greatly alter longevity research not only to tackle age-related defects but also to possibly reverse the cellular ageing process. Partial reprogramming enables the resetting of the ageing clock without erasing cellular identity.

Delivery remains challenging. Getting the therapy into all necessary cells throughout the body requires sophisticated vectors. We're making progress - Wuhan Neurophth Biotechnology is recruiting for a phase 1/2/3 clinical trial of an ND4 gene therapy for LHON patients expected to conclude in 2027. For LHON patients suffering from vision loss, the promising results could be a first-in-class targeted gene therapy for a single gene mtDNA disease. But that's for a single organ, the eye. Systemic delivery is far more complex.

My view? Allotopic expression is essential but insufficient alone. The engineering elegance appeals to me - directly solving the problem rather than managing symptoms. But we need combination approaches targeting all damage types. That's precisely why our RMR2 study combines multiple interventions. No single magic bullet exists for aging.

Additional sources: https://www.lifespan.io/news/nuclear-expression-of-a-mitochondrial-gene-in-mice/ https://sens.org/sensible-question-how-secure-a-mitochondrial-backup-is-allotopic-expression/ https://pubmed.ncbi.nlm.nih.gov/14573482/ https://pmc.ncbi.nlm.nih.gov/articles/PMC8962324/